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. 2023 Feb 14;18(2):e0280981. doi: 10.1371/journal.pone.0280981

Prevalence of asymptomatic malaria infection by microscopy and its determinants among residents of Ido-Ekiti, Southwestern Nigeria

Azeez Oyemomi Ibrahim 1,2, Ibrahim Sebutu Bello 3,*, Adewumi Oluwaserimi Ajetunmobi 1, Abayomi Ayodapo 4, Babatunde Adeola Afolabi 5, Makinde Adebayo Adeniyi 6
Editor: Luzia H Carvalho7
PMCID: PMC9928065  PMID: 36787321

Abstract

Background

Asymptomatic malaria infections have received less attention than symptomatic malaria infections in major studies. Few epidemiological studies on asymptomatic malaria infections have often focused on pregnant women and children under-five years of age as the most vulnerable groups. However, there is limitation on data regarding asymptomatic infections among the old adult populations, particularly in the study area. Therefore, this study determined the prevalence of asymptomatic malaria infection by microscopy and its determinants among residents of Ido- Ekiti, Southwestern Nigeria.

Methods

A hospital-based cross-sectional study was conducted between July and September 2021 among 232 consenting apparently healthy individuals aged 40 years and above who were recruited during a free health screening program using a standardised interviewer-administered questionnaire. The questionnaire sought information on respondents’ socio-demographics, presence and types of co-morbidity, and the prevention methods being adopted against malaria infection. Venous blood samples were collected and processed for asymptomatic infections using Giemsa-stained blood smear microscopy. Data were analysed using SPSS version 21. Multivariate logistic regression was used to identify factors associated with asymptomatic infections.

Results

Of the total 232 respondents, 19.0% (48/232) were confirmed to be infected with Plasmodium falciparum (95% confidence interval (CI): 14.1% - 24.6%). Lack of formal education (Adjusted odds ratio (AOR): 5.298, 95% (CI): 2.184-13.997), being diabetic (AOR: 4.681, 95% CI: 1.669-16.105), and not sleeping under Long Lasting Insecticide Net (LLINs) (AOR: 4.594, 95% CI: 1.194-14.091), were the determinants of asymptomatic Plasmodium falciparum infection.

Conclusion

The prevalence of asymptomatic Plasmodium falciparum was 19%. Lack of formal education, being diabetic, and not sleeping under LLINs were the determinants of asymptomatic infections.

Introduction

Asymptomatic malaria infections remain a global public health problem with consequences for human health, as well as social and economic development [1]. Asymptomatic malaria infections refer to the presence of asexual parasites in the peripheral blood without symptoms [2]. Individuals with asymptomatic malaria infections, especially in the adult population have been identified as providing a reservoir for malaria transmission and a precursor in the progression to symptomatic disease [3]. The infections are highly prevalent in endemic areas of Sub-Sahara Africa (SSA), with only a small percentage of individuals exhibiting clinical symptoms [3]. This has grave consequences for malaria control programs [4]. Hence, Asymptomatic malaria infections are recognised as an important obstacle to malaria elimination as it plays a critical role in delaying the global elimination of malaria [5, 6].

Previous studies have shown that after exposure to malaria parasites, a clinical immunity only partially develops depending on some variations such as endemicity, mode of prevention adopted and co-occurrence of co-morbid conditions [7, 8]. Other studies have suggested that increased poverty levels, poor access to quality health care, and unlimited exposure to mosquito bites in rural settings threaten the integrity and sustenance of such partial immunity, especially in the old age categories [9, 10]. It is because of these reasons that advocacy for malaria prevention strategies such as the use of Long-Lasting Insecticide Treated Nets (LLINs), Indoor Residual Spray (IRS), and other measures were introduced to reduce the incidence of asymptomatic infections, especially in rural settings [9]. To eradicate malaria, researchers have advocated for screening individuals for asymptomatic infections using highly sensitive and accurate diagnostic tools. The use of sustained integrated vector control efforts and drug treatment in areas of high-risk populations have also been advocated [11, 12].

Asymptomatic malaria infections have received less attention than symptomatic malaria infections in major studies [5, 7]. Few epidemiological studies on asymptomatic malaria infections have often focused on pregnant women and children under five as the most vulnerable groups [6, 13]. To the best of our knowledge, there has been no published study to attest to the epidemiological data regarding asymptomatic malaria infections among the old adult populations. Yet, the old adult populations are vulnerable to diseases and illnesses due to their physiological state [2, 9, 14]. This is very important because the economic implications of these illnesses on the old adult populations would generally reflect on the well-being of the families, communities, and nations [9]. Thus, the present study determined the prevalence of asymptomatic malaria infections by microscopy and its determinants among residents of Ido-Ekiti, Southwestern Nigeria.

Materials and methods

Study area/design/period

A hospital-based cross-sectional study was carried out at the family medicine clinic, federal teaching hospital, Ido-Ekiti, between July and September 2021 among apparently healthy residents of Ido-Ekiti, Southwestern Nigeria. The study was conducted during the annual free health programs organised for the residents of the community by the hospital chapter of the society of family physicians of Nigeria. The theme of the programs was “screening for communicable and non-communicable diseases among residents of Ido-Ekiti” The hospital is situated at a location central to the host community. Ido-Ekiti is a rural community in Ekiti State. It has a total land area of 332 km2 and a total population of 159,114 inhabitants, according to the most recent population census conducted in 2006. The annual population growth rate is 3.2%, with the population in 2019 estimated to be 225,305 inhabitants [15]. Ido-Ekiti is located in a tropical rainforest with climatic and environmental conditions that support the growth of malaria transmission. Residents of Ido-Ekiti are mainly farmers and traders in the informal sector, with a relatively small proportion comprising the working population and retirees in the formal sector [15]. In the study area, malaria transmission is perennial during the wet season (April – October), with Plasmodium falciparum being the major causative agent. The family medicine clinic offers primary and specialist care for a wide array of acute and chronic medical conditions to individuals in its catchment and the surrounding area.

Source population

This comprised all adult individuals who were residents in Ido-Ekiti, and who presented for the annual free health programs organised by the society of family physicians of Nigeria.

Study population

The study population comprised apparently healthy individuals aged 40 years and above.

Inclusion/Exclusion criteria

Consented apparently healthy individuals aged 40 years and above, permanent residents in the host community, have no travel history for at least a week, axillary temperature ≤ 37.5°c, showed no recent history of fever in the past 48 hours, and any other clinical symptoms of malaria such as headache, dizziness, joint pain, anorexia and malaise were included in the study. Individuals who were too ill that required immediate attention, pregnant women, or those on treatment for malaria or had just completed anti-malaria treatment within two weeks before the conduct of this study were excluded.

Sample size determination

This was determined using the formula [16], n = Z2 P(1-P)/d2 with a prevalence (P) of 16.2% [2] of asymptomatic Plasmodium falciparum infection reported in a cross-sectional study among the older population in Southwestern Nigeria, at 95% confidence interval (CI) and 5% margin of error. In this calculation, Z = 1.96, P = 0.162, 1-P = 0.838, and d = 0.05. This gave a minimum sample size (n) of 209. This was increased to 232 to cover dropouts.

Sampling method

Systematic random sampling technique was used in this study. The sampling frame is the total number of asymptomatic individuals expected during the study period. Data from the records department for 2018 free health screening among apparently healthy individuals gave a sampling frame of 950. Dividing the sampling frame by the sample size (232) gave a sampling interval of four (4). On each screening day, the fourth registered respondent was selected by systematic random sampling technique. After that, every fourth respondent was selected. This process was repeated on each clinic day throughout the study period until the sample size of 232 was attained. Recruited individuals had their record cards tagged to prevent re-enrolment. The recruitment of the subjects was done by three trained resident doctors in the department who served as research assistants while the researcher did the collection of data.

Study protocol

The study instrument was translated from the English language to Yoruba by professional linguists. The process involved forward and back translation. Both the English and Yoruba versions of the questionnaires were used during the study, depending on the language preference of the subject. Pre-testing of the questionnaire was done in a similar group of subjects at the family medicine department of a nearby sister health facility. Adjustments were made to the study instrument based on evidence from the pre-test.

Data collection instruments

The two instruments for data collection were the standardised interviewer-administered questionnaire and the data collection form. The questionnaire sought information about the respondents’ socio-demographic characteristics (such as age, gender, education, occupation, and location), mode of malaria prevention adopted by them, and their past medical history. They were also assessed for the presence of co-morbid conditions such as hypertension, diabetes mellitus, Human Immunodeficiency Virus/ Acquired Immune Deficiency Syndrome (HIV/AIDS), Chronic Obstructive Pulmonary Disease (COPD) and Heart failure. These were self-reported.

Clinical parameters of the respondents

Microscopy for asymptomatic infections

Capillary blood samples were collected by finger pricking using a disposable lancet. The thick and thin films were made from the blood sample. The thick and thin smears were prepared on clean, dry microscope glass slides and were allowed to dry. The thin smear was fixed in methanol, and both smears were stained with 5% Giemsa. The stained slides were taken to the hospital laboratory, where parasitological examinations were made independently by two malaria microscopists, with discrepancies resolved by a senior microscopist who ensured quality control. A slide was declared negative if parasites were absent after examining 200 high-power fields. Parasite density was quantified against 200 leucocytes on an assumed leucocyte count of 8000 per ul of blood [17]. The degree of parasite density was graded as mild, moderate, and severe when the counts were between 1-999 parasites/ul, 1000-9999/ul, and > 10,000/ul, respectively, following the method described elsewhere [18].

Parasites/ul = No. of asexual stages x 8000 leukocytes/200 leukocytes

Determination of packed cell volume (PCV)

A micro-haematocrit tube was filled with blood and centrifuged in a micro-haematocrit rotor at 10,000 rpm for 5 minutes. PCV was read using the micro-haematocrit reader and recorded as no anaemia (PCV≥30%), mild anaemia (25-29%), moderate anaemia (20-24%), and severe anaemia (<20%) [19].

Ethical consideration

The study protocol was approved by the Ethics and Research Committee of Federal Teaching Hospital, Ido-Ekiti, Ekiti State, Nigeria (ERC/2021/06/25/605A). When seeking consent from the respondents, the methods and objectives of the study were explained clearly to the respondents individually. The respondents were told they were free to refuse or disengage participation at any time without losing any benefit of care or favour to those who participated. Thus, informed written consent was obtained from each respondent before starting the study. Data collected from each respondent and results of laboratory tests were kept confidential, and privacy was ensured throughout the study. The study was at no cost to the respondents.

Treatment of the respondents

The results of the laboratory tests were addressed to the respondents, and all malaria parasite asymptomatic individuals were treated in accordance with the treatment guideline for individuals with asymptomatic infections [20]. The reporting of this study conforms to the strengthening of the Reporting of observational studies in Epidemiology (STROBE) statement [21].

Operational definitions

Asymptomatic infections

This is the presence of an asexual parasite in the peripheral blood, in the absence of fever or other acute symptoms, in individuals who have not received recent anti-malarial treatment [22].

Old adult

This is referred to as 40 years of age and above in this study and is classified as middle-aged (40-59) and elderly (≥60 years of age).

Window net

This is a physical barrier that is placed across the window in a building to prevent Anopheles mosquitoes from entering the room.

Statistical analysis

Data were coded, cleaned, entered, and analysed using IBM SPSS for window version 21.0 (IBM Corp., Armonk, NY, USA), respectively. Quantitative data were expressed as mean ± standard deviation. Frequencies were used to determine the respondents’ prevalence of asymptomatic Plasmodium infection. Binary logistic regression was employed to assess the determinants of asymptomatic Plasmodium infection. Variables significant at P-value < 0.05 in the univariate logistic regression were selected for multivariate logistic regression analysis model. Odds ratios with 95% confidence intervals were calculated and P-value< 0.05 was considered statistically significant.

Results

Socio-demographic characteristics of the respondents

A total of 232 respondents were studied. The age of the respondents ranged from 40- 83 years with a mean age of 59.3 ± 12.7 years, the majority (59.5%) of them between 41-60 years. The majority of the respondents (65.5%) were males, and about 32.0% of them completed their tertiary education. The majority (68.1%) were rural dwellers, and (71.6%) were of lower income earners (Table 1).

Table 1. Socio-demographic characteristics of respondents (N=232).

Variables Frequency Percentage
Age (In years)
40-59 (middle-aged) 134 57.8
≥ 60 (elderly) 98 42.2
Mean age ± 59.3±12.7
Sex
Made 152 65.5
Female 80 34.5
Occupation
Farmer 33 14.2
Artisan 41 17.7
Trader 70 30.2
Civil Servant 72 31.0
Retirees 16 6.9
Education
Primary 21 9.1
Secondary 75 32.3
Tertiary 60 25.9
Domicile
Rural 158 68.1
Urban 74 31.9
Income
Low (<27,101Naira) 166 71.6
High (≥ 27,101Naira) 66 28.4
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27,101 Naira is the monthly equivalent of $2.2 per day at $1 equals to 410.63 Naira as at July 2021.

Prevalence and parasite density among asymptomatic infections by respondents

In all, 19% (44/232) of the respondents were positive for asymptomatic infections (95% CI: 14.1% - 24.6%), with only P. falciparum species identified from thin blood smear. Of the 44 diagnosed with asymptomatic Plasmodium infection, 28 (12.1%), 14 (6.0%), and 2 (0.9%) had mild, moderate, and severe parasitaemia respectively (Table 2).

Table 2. Prevalence and parasite density of asymptomatic infections by Microscopy (N = 232).

Variable Frequency Percentage
N = 232 (%)
Asymptomatic infections by density
Mild parasitaemia (< 1000 parasites) 28 12.1
Moderate parasitaemia (1000 – 9999) 14 6.0
Severe parasitaemia (≥ 10000) 2 0.9
Prevalence
Positive 44 19.0
95% Confidence Interval (Lower – Upper) 14.1% - 24.6%
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Using multivariate logistic regression for factors associated with asymptomatic P.falciparum infection in this study, after adjusting for possible confounders; the odds of being infected with P. falciparum was 5.298 times (95% CI: 2.184-13.997) higher among the respondents who had no formal education, 4.68 times (95%CI: 1.669-16.105) higher among the respondents who were diabetes, and 4.594times (95% CI: 1.194-14.091) higher among the respondents who were not sleeping under LLINs (Table 3).

Table 3. Multivariate logistic regression for the significant factors associated with asymptomatic infections.

Variable +ve (%) -ve (%) COR (95% CI) p-value AOR (95% CI) p-value
Age (in years)
40 – 59 (ref) 18(13.4) 116(86.6) 1.000 1.000
≥60 26(26.5) 72(73.5) 2.327 (1.192 – 4.544) 0.012 1.975 (0.491 – 5.395) 0.290
Occupation
Farmer 13(39.4) 20(60.6) 4.550 (0.884 – 23.407) 0.055 6.123 (0.228 – 16.693) 0.281
Artisan 8(19.5) 33(80.5) 1.697 (0.319 – 9.022) 0.532 4.259 (0.179 – 10.388) 0.370
Trader 12(17.1) 58(82.9) 1.448 (0.290 – 7.222) 0.650 2.776 (0.116 – 6.529) 0.529
Civil Servant 9(12.5) 63(87.5) 1.000 (0.194 – 5.145) 1.000 0.589 (0.026 – 13.587) 0.741
Retiree(ref) 2(12.5) 14(87.5) 1.000 1.000
Education
None 13(61.9) 8(38.1) 16.018 (4.948 – 51.858) <0.001 5.298 (2.184 – 13.997) 0.007
Primary 15(20.0) 60(80.0) 2.464 (0.0.942 – 6.446) 0.060 3.878 (0.445 – 7.791) 0.220
Secondary 9(15.0) 51(85.0) 1.732 (0.608 – 4.981) 0.298 2.189 (0.239 – 10.027 0.488
Tertiary(ref) 7(9.2) 69(90.8) 1.000 1.000
Domicile
Rural(ref) 24(15.2) 134(84.8) 1.000 1.000
Urban 20(27.0) 54(73.0) 2.068 (1.056 – 4.050) 0.032 2.883 (0.889 – 9.349) 0.078
Diabetes Mellitus
Yes(ref) 22(78.6) 6 (21.4) 30.333 (11.148 – 87.495) <0.001 4.681 (1.669 – 16.105) <0.001
No 1.000 1.000
Insecticide treated net
Yes(ref) 1.000 1.000
No 43(23.9) 137(76.1 16.007 (2.148 – 119.295) <0.001 4.594 (1.194 – 14.091) 0.033
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ref – reference category COR – Crude Odd Ratio AOR – Adjusted Odd Ratio.

Discussion

The study identified the prevalence of asymptomatic Plasmodium falciparum infection and its determinants among individuals 40 years of age and above, resident in Ido-Ekiti, Southwestern Nigeria. An overall prevalence of asymptomatic P. falciparum infection in this study was 19.0% (95% CI: 14.1% - 24.6%), which is similar to 16.2% reported in a cross-sectional study among the asymptomatic elderly population in Oshogbo, Southwestern Nigeria [2]. This may be due to the similarity in the study population, geographical location, climatic and environmental factors. However, a higher prevalence of 50.0% asymptomatic P. falciparum infection was reported in a cross-sectional study conducted in Ilorin, North-central Nigeria [23], while another cross-sectional study in Akure Southwestern Nigeria by Adepeju et al. had reported prevalence of 53.3% asymptomatic P. falciparum [24]. While our own study was among the respondents categorised as middle-aged and old adults, the other studies were among the respondents categorised as young adults. This difference agrees with the finding of another study that the prevalence of asymptomatic P. falciparum falls as age increases [25]. On the contrary, another cross-sectional study conducted on the prevalence of asymptomatic P. falciparum infection in a rural district in Gabonese adults had reported a prevalence of 12% [26], which was lower than the finding in this study. The observed difference in the prevalence of our study compared to these other studies may be due to variations in the study design, study period, and climatic factors. This is because climate variations among study areas have an effect on the life cycle of parasites and parasite adaptation among Plasmodium falciparum infections.

The current study has identified factors associated with asymptomatic infections. The respondents who had no formal education were 5.298 times more likely to have asymptomatic infections compared to other respondents who had formal education. The result agrees with the reports of other studies that showed that the level of education significantly influences people’s knowledge, attitude, and practices, which in turn could lead to reduced malaria infection [27, 28]. However, other studies have reported that people can be acquainted with the knowledge of malaria transmission, prevention, and control irrespective of their educational status [29, 30].

Similarly, the respondents with T2DM were at increased odds of asymptomatic P. falciparum infection compared to other co-morbidities. This was in agreement with a previous cross-sectional study conducted in Lagos, which reported that type 2 diabetic individuals harboured asymptomatic P. falciparum infection [14]. Furthermore, the finding in the current study was also in agreement with another cross-sectional study conducted in rural Southwestern Nigeria where it was reported that individuals with type 2 diabetes mellitus were associated with the presence of asymptomatic P. falciparum [31]. The findings in the current study and these other studies suggest that adult-type diabetic individuals were potential reservoirs of asymptomatic infections. The mechanisms of occurrence of asymptomatic malaria infections in adult T2DM are not completely understood. However, a recent study from central Africa has attributed the association to anti-parasitic immunity, which prevents parasitaemia from reaching a clinical level called pyrogenic threshold and for preventing secondary infection in adults with primary asymptomatic infections [32]. Other studies have linked the association between asymptomatic infections and individuals with T2DM to increased mosquito bites, and olfactory signals mediate mosquito attraction [14, 31, 33]. The current finding calls for the investigation of high-risk individuals aged 40 years and above for asymptomatic carriage of malaria parasites as an intervention for ensuring malaria elimination. Contrary to our findings, other authors have reported symptomatic infections among individuals with T2DM [9, 34].

In the same vein, using LLINs was found to be protective against asymptomatic infections as the data showed that respondents who did not sleep under LLINs were five times more likely to have asymptomatic infections as compared to respondents who slept under LLINs. This finding agrees with a previous cross-sectional study conducted among the elderly population in Oshogbo, where it was reported that individuals who did not sleep under LLINs were at increased risk of asymptomatic infections [2]. Appropriate utilisation of LLINs is one of the major cost-effective interventions for malaria prevention [23]. This finding calls for a continuous awareness campaign on the usefulness and usage of LLINs in rural settings. However, a cross-sectional study conducted in Abuja, Nigeria by Onyiah et al., had found no association between individual LLIN use and asymptomatic infections [35].

Limitations

Firstly, the study was based on a cross-sectional design and, thus, had limited opportunities to measure any causal association between asymptomatic infections and other factors. Microscopy instead of polymerase chain reaction (PCR) was used to diagnose asymptomatic infections in this study. We may therefore have underestimated the burden of asymptomatic infections given the fact that PCR sensitivity can extend to below one parasite per microlitre [36]. However, PCR was not used in this study due to non-availability in our facility. Also, the information provided on preventive methods was self-reported and could not be verified. Therefore, ultimate corroboration would need a prospective longitudinal study controlling for exposure. Despite these limitations, the study generates vital information regarding the burden and the associated risk factors for asymptomatic infections, which could be helpful in the formulation of further steps to implement control interventions.

Conclusion

In this study, the prevalence of asymptomatic P. falciparum infection was 19.0%. The respondents with informal education, diabetes mellitus and those not sleeping under LLINs were identified as determinants of asymptomatic infections. Strategies promoting LLINs use need to be intensified and should be complemented by awareness campaigns against asymptomatic infections in Ido- Ekiti.

Supporting information

S1 File. Dryad data set.

(PDF)

Click here for additional data file. (595.8KB, pdf)
S1 Data. ASM data.

(XLSX)

Click here for additional data file. (25.9KB, xlsx)

Acknowledgments

The authors expressed profound gratitude to the hospital chapter of the society of family physicians for the free health programs, which provided an avenue to conduct this research. Appreciation goes to the resident doctors and nurses in the family medicine department. The authors also thank our respondents for making themselves available for the research.

Data Availability

The dataset is in the Dryad repository and can be accessed with the following DOI: https://doi.org/10.5061/dryad.gqnk98ssx.

Funding Statement

The authors received no specific funding for this work.

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Decision Letter 0

Luzia H Carvalho

26 Sep 2022

PONE-D-22-24029Socio-Demographic Profiles, Co-Morbid Conditions and Preventive Measures as Determinants of Asymptomatic Malaria Infections Among Older Age Population in Rural Southwest NigeriaPLOS ONE

Dear Dr. Bello,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Nov 10 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Luzia H Carvalho, Ph.D.

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at 

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and 

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2. Please amend your current ethics statement in the Materials and Methods section of your manuscript to include the full name of the ethics committee/institutional review board(s) that approved your specific study.

3. We note that you have stated that you will provide repository information for your data at acceptance. Should your manuscript be accepted for publication, we will hold it until you provide the relevant accession numbers or DOIs necessary to access your data. If you wish to make changes to your Data Availability statement, please describe these changes in your cover letter and we will update your Data Availability statement to reflect the information you provide.

Additional Editor Comments:

After careful consideration, we felt that your manuscript requires revision, following which it can possibly be reconsidered. Although your manuscript was of interest to the reviewer, major concerns were related to study design and results.  As stated by the reviewers the definition of ASM may be seriously flawed, given that the study population comprised of individuals visiting a hospital due to illness and with malaria parasites. The interpretations of the statistical analyses also need to be revised. In addition, a significant number of issues should be clarified and/or adjust otherwise the MS’s results may be compromised. Finally, we strongly suggest that the MS should be submitted to a copy-editing process. For your guidance, a copy of the reviewers' comments was included below. 

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: No

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: No

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: 1. Title needs modification. Because, it does not much with your objective. So, I recommend your title to be modified as’’ Prevalence of asymptomatic malaria infection and its determinants among older aged patients attending a tertiary hospital in rural Southwestern Nigeria. In addition, what does older aged mean? You have to give clear definition in your operational definition section.

2. In line number 5, you have to write the Authors’ name with superscript first and write their affiliations in increasing order using super scripts. You can give similar super script number for authors at the same affiliation and separate corresponding Author with star mark from other authors. So, remove email, ORCid etc from each. You have to also write all the abbreviations in full terms here.

Lines24 – 27 write as: *Correspondence author: Ibrahim Sebutu BELLO

Email: bello.ibrahim@gmail.com. This one is enough and remove other sentences

3. Abstract:

Here, there is no background section. You have to write the background with statement of the problem in short and show clear message before putting objective.

The objective remains true only if you modify your title as I mentioned earlier.

4. Methods:

Rewrite lines 31-34 clearly including study period, kind of cross sectional design whether community based, health facility based, school based etc.

5. Results: line 39-40, write “being diabetes” as “being diabetic”

6. Conclusion:

Lines 44-45 “The findings may guide ….” is not vital here. But, you have to describe the key findings, for example, prevalence, species and key determinants/factors/ associated.

Introduction

Line49: ref[1] you used is not about ASM. But, it is about worldwide prevalence of anemia. Even it is too old. Please use appropriate citation and remove this.

Methods and materials

Line87: Write Study design area and period as subtitle/ heading2/, then, write like” A hospital based descriptive cross sectional study was carried out at… from …to … (i.e period) ”

What is descriptive cross sectional study design mean?

Line89: the census data (2006) is too old. Can’t you find current/ updated/ data?

Remove line 97. Since, I have mentioned it to write at the beginning of method section.

Line 100: why do these older aged (despite its definition in need?) persons came to hospital? Since they are asymptomatic and your study also is on asymptomatic cases. People with no signs/ symptoms do not attend health institutions. So, how did you get your study subjects in tertiary hospital?

In addition, elderly people especially those above 60 usually remain symptomatic if bitten as they have suppressed immune system. So, how can they remain asymptomatic and be your study subjects. That is why I asked you to operationalize “older aged patients” at the very beginning. I want to hear clear cut of age you used in your study.

Line 104: Also, those … anti-malarial (put treatment) ….

Line 106: sample size… can you clearly show us how you calculated sample size? Here, 16.8% prevalence you used is that obtained by PCR in previous study. So, why did you use PCR value rather than using the value obtained by Microscopy (i.e 7.2%) since the method you conducted to detect ASM is microscopy.

Line 120: remove “The study was conducted between July and October 2021” as I informed you to write in “Study design, area and period section”.

Line 148 – 149: What about to determine P. vivax and other species?

Reference [18] is placed in two areas; lines 143-144 and line 156, which are very far and different ideas. Please write appropriate citation for these ideas each.

Lines 162- 165: According to the national malaria drug policy, …. These sentences are the same and identical with the sentence in lines 143-145, but, with different references. Please see it again and remove either of.

Results

Please describe the species detected!

Line 176: write as “in all, only 19% (44/232)…”

Table1: what were your criteria to classify parasitemia as mild, moderate and severe?

Line 182-184, do you mean the association is in binary logistic regression?

Line 185-187: how do you see the positivity rate of ASM in age groups of 61-80 years old, farmers and informal education? Is that the reality? They have to be symptomatic rather than asymptomatic carriers especially those in 61-80 yrs.

Table 2: in your income classification, is 1.9 dollars daily/weekly/ monthly income? How did you take 1.9 dollar as base line to classify income? Why not 2, 3…or other dollars?

Line 191-193: Do you think that co morbidity does not worsen the signs/symptoms of malaria? For example, why do people with diabetes remain asymptomatic for malaria than non-diabetic?

Line 205: what is window net? Is it physical or chemical barrier? How is it applied?

Table6: here you used Odds ratio as measure of association. But, you applied chi-square in the above. Why do you need to apply two different measures of association? Why couldn’t you use either of one in all?

Discussion

Line 226: put CI in prevalence. B/c the reader can easily understand and compare your value with the values of other studies.

Line 229: reference [21] does not much with the data you used to compare your result. Please see it again.

Line 235-236: However, other studies have disagreed with this report [23, 24]. What was the report of other studies here? You have to specify so that the readers can easily understand. By the way, reference 23 is not relevant and not used to compare your study which is ASM. But, that one is done from febrile/symptomatic/ patients and hence you have to remove.

Line 240: ref [26] can’t be used to compare your study. B/c that study was among children while yours is among older aged. Please note that; in discussion, you have to use the data from the studies among similar study subjects, similar methodology, similar disease condition/asymptomatic only/ etc.

Line 254: …but opposite to several other studies [14, 27]. What do you mean by opposite? Is that lower/ higher? Also please specify the number when you say consistent, higher/ lower in each section so as to make clear for the readers.

Line 259: This may be further aggravated by the low immunity of urban dwellers. Why is the immunity of urban dwellers low?

Line267- 275: In this study, the respondents with mild and moderate anaemia…

This is not your concern and is out of your objective and hence no need to discuss about. Remove it.

Acknowledgement: if this section is needed, why don’t you acknowledge your study participants? They are everything for your study.

General comment: Italicize the genus and species names of parasites/ microorganisms in every section

Reviewer #2: Socio-Demographic Profiles, Co-Morbid Conditions and Preventive Measures as

Determinants of Asymptomatic Malaria Infections Among Older Age Population in

Rural Southwest Nigeria

Review Comments

General: The aim was to assess the prevalence and determinants of asymptomatic infections among individuals 40 years of age and above, resident in a rural community of Ekiti State, Nigeria. The study attempts to present useful information regarding malaria among the elderly, however the definition of ASM may be seriously flawed, given that the study population comprised of individuals visiting a hospital due to illness and with malaria parasites. Thus, the study population can be classified as having clinical malaria and not asymptomatic infection. The interpretations of the statistical analyses are inaccurate. Revision of the language to improve readability, particularly of the introduction sections, using a copy-editing tool, is recommended.

The following minor and major corrections/suggestions could help improve the manuscript:

Title: The authors may consider putting the name of the rural community in the title. The title should indicate that asymptomatic infections were determined by microscopy

Abstract: Overall, there is coherence in abstract but could be improved.

Line 31 to 34: Authors should consider restructuring the sentence to improve readability.

Methods: Authors should consider inclusion of the year of the cross-sectional sampling and the name of the rural community where samples were drawn, in the abstract.

Conclusion line 43: The ‘arguments for high prevalence of asymptomatic malaria in rural settings’, are not shown in results, so the sentence should be clarified.

Introduction: Authors should consider revising the language to improve readability, using a copy-editing tool.

Line 49 to 51: The presence of malaria parasitaemia without symptoms of illness may best be described as an asymptomatic infection, so authors should consider replacing asymptomatic malaria with asymptomatic (malaria) infection.

Line 75 to 78: There are many old-age-associated diseases with socio-economic implications, and planning an effective malaria control programme is not entirely dependent on knowing the prevalence of asymptomatic infections among the elderly. The highest burden of malaria is among children under five years of age, who are the target of several interventional programmes, so the rationale for the study is weak.

Materials and methods:

Line 87: Authors should provide the names of the study institution and the rural community.

Line 97 to 99: Authors should note that an infection identified during a hospital visit will not qualify as asymptomatic.

Line 100: Authors should specify ‘recent history’ (eg. 24 or 48 hours ago or a week ago etc.) in their inclusion criteria/definition of asymptomatic infection

Line 104: Why did Authors exclude individuals with mental illness? Was axillary temperature ≥ 37°C also excluded?

Line 110 to 120: The procedure of the systematic sampling is impressive, however, it is unclear why the sampling is considered random, as the selection of the first respondent appears systematic.

Line 147: May not be relevant.

Line 148, 157: Authors should structure as a minor heading, removing the indent.

Line 161 to 163: Authors should ensure that the referenced treatment guidelines are for the asymptomatic infections (study target population) and not management of clinical malaria.

Authors should provide a clear definition of asymptomatic infection in the methods section.

Results: The authors aim to demonstrate association between several predictor variables and asymptomatic infections, however, the lack of a clear definition for asymptomatic infection (ASM) detracts from the integrity of the data collected. Specifically,

Line 176: Of respondents who tested positive for parasitaemia, how many had symptoms?

Line 179, Table 1: The proportion of individuals testing negative has not been shown to have asymptomatic infections (by PCR) and so should be removed from Table 1, or the heading re-worded. The individuals testing negative should not be placed under the heading ‘Asymptomatic Malaria Parasitaemia’ in the table.

Line 183 to 203: Table 2, 3 and 4 show the distribution of microscopy positive and negative tests by age, sex, occupation etc… and whether the overall differences in the distribution are significant. The tables do not show association between the predictor variables and asymptomatic infections (ASM). Authors should present their results/data properly, for statistical accuracy.

Line 188, Table 2: The reference variables are unclear, if association between the predictors and ASM is the goal. The negative population may or may not have malaria parasites by PCR, so ‘Malaria’ should be replaced with the word ‘Microscopy’.

Line 216, Table 6: The response variable (malaria test positive with or without symptoms = ASM?) for which the regression analyses was performed is missing from the table, so it is difficult to understand how the results were interpreted by the authors.

Discussion: The discussion reads well, based on the results presented. However, due to the lack of a clear definition for ASM and inaccurate interpretations of the statistical analyses, the discussions and conclusions cannot be scientifically supported. The discussion should be re-written after the corrections in the other sections.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Attachment

Submitted filename: Review comments.docx

Click here for additional data file. (22.1KB, docx)

Decision Letter 1

Luzia H Carvalho

7 Dec 2022

PONE-D-22-24029R1Prevalence Of Asymptomatic Infections By Microscopy And Its Determinants Among Residents of Ido-Ekiti, Southwestern NigeriaPLOS ONE

Dear Dr. Bello,

Thank you for submitting your manuscript to PLoS ONE. After careful consideration, we felt that your manuscript requires substantial revision, following which it can possibly be reconsidered, thus governing the decision of a “major revision”. As requested by the reviewer, the authors still need to address specific issues, particularly related to the data analysis, methods and results. For example, a previous concern on regression analysis section was not addressed. At this point, we strongly recommend that the authors include/clarify all topics raised by the reviewer. For your guidance, a copy of the reviewers' comments was included below.

Please submit your revised manuscript by Jan 21 2023 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Luzia H Carvalho, Ph.D.

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Authors have addressed the previous comments well. But, here are some minor comments and suggestions to make the manuscript better for the readers and scientific community. While responding, It is better if authors give point by point response.

Minor comments:

I think it is good to add the word “malaria” in your title (Prevalence of asymptomatic malaria infection…)

Abstract:

The back ground (Line 23 – 27) is still not adequate. You have to show the gap. I suggest writing as “Asymptomatic infections have received …. Few epidemiological studies on …However; there is limitation on data regarding asymptomatic infections among the old adult populations particularly in the study area. Therefore, this study determined the prevalence of asymptomatic infections by microscopy and its determinants among residents of Ido- Ekiti, Southwestern Nigeria.”

Materials and methods

Authors have put “study population” which is good. But, they also have to write “Source population”

Line 185” Quantitative data were… (Change “are” to were).

Result:

My previous concern on regression analysis section is not addressed. For example, why did you use different measures of association? In tables 3,4 and 5 you used chi-square, But, Odds ratio in table 6. In column, you have to write the number of negatives in each category. You only put number of positives and total. You can leave total, but replace it with negatives. That is why the odds ratios which you put in table 6 are not right through direct manual calculation. Odds ratio remains true if you put Negative column rather than the total making it clear for the readers.

Discussion:

Line 257 – 258: An overall prevalence of asymptomatic P.falciparum infection in this study was 19.0% (95% CI: 14.1% - 24.6%), which is similar to…

Line 264: P.falciparum

Line 275: … 5.298 times more likely to have…

Line 283: Why do type 2 diabetic individuals harbour asymptomatic P. falciparum infection rather than developing symptoms?

Line 296: … five times more likely…

General question: The species detected in your study area was P.falciparum only. How much accurate were you? Who examined the slides? Is the area known by presence of this species only? If not, I expect that there might have been error in species identification in your study.

Finally, align all texts to both the left and right sections. I think all the text is aligned to the left only in your document.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2023 Feb 14;18(2):e0280981. doi: 10.1371/journal.pone.0280981.r004

Author response to Decision Letter 1

20 Dec 2022

Summary of reviewer’s comments and Authors’ response (PONE-22-24029R1)

Reviewer: 1

comments Response from Author:

Authors have addressed the previous comments well. However, there are minor comments and suggestions to make the manuscript better for the readers and scientific community.

Minor comments:

I think it is good to add the word “malaria” in your title (Prevalence of asymptomatic malaria infection..)

Abstracts:

The background is still not adequate. You have to show the gap. I suggest writing “Asymptomatic infections have received--- Few epidemiological studies on …However; there is limitation on data regarding asymptomatic infections by microscopy and its determinants among residents of Ido-Ekiti, Southwestern Nigeria”

Materials and methods:

Authors have put “ study population” which is good. But, they also have to write” Source population”

Line 185 “Quantitative data are (Change “are” to were)

Results:

My previous concern on regression analysis section is not addressed. For example, why did you use different measures of association? In table 3,4, and 5 you used chi-square, But Odds ratio in table 6. In column, you have to write the number of negatives in each category. You only put number of positive and total. You can leave total, but replace it with negatives. That is why the odds ratios you put in table 6 are not right through direct manual calculation. Odds ratio remains true if you put negative column rather than the total making it clear for the readers.

Discussion:

Line 257-258: An overall prevalence of asymptomatic P. falciparum infection in this study was 19.0% (95% CI: 14.1%-24.6%), which is similar to—

Line 264: P. falciparum

Line 275: --5.298 times more likely to have….

Line 283: Why do type 2 diabetic individuals harbor asymptomatic P. falciparum infection rather than developing symptoms?

Line 296:….. five times more likely……

General questions:

The species detected in your study area was P. falciparum only. How much accurate were you? Who examined the slides? Is the area known by the presence of this species alone? If not, I expect that there might have been error in species identification in your study.

Finally align all texts to both the left and right sections. I think all the text is aligned to the left only in your document.

Thank you for the efforts put in to review and improve our manuscript.

Line 1: The word “malaria “ has been added to the title.

Abstract:

Line 21-47: The background has been improved and has addressed the suggestions.

Materials and methods

Line 106-107: Source population has been included.

Line 186: The word “are” has been changed to “were”

Results:

This comment has been addressed. Only one measure of association was now used, which are the odds ratios.

Discussion:

Line 228-229: This has been addressed.

Line 235: This has been addressed

Line 246: The word “as likely “ has been changed to “more likely”

Line 260-264: The association between type 2 diabetic individuals and asymptomatic has been addressed on page line

Line 271: Five times “as likely” has been changed to “more likely”

There was no error in species identification in this study. P. falciparum has been the only species known to be prevalent in Southwestern Nigeria and this observation has been corroborated by several studies in Southwestern Nigeria. Check references 7,14,35.

The stained slides were taken to the hospital laboratory, where parasitological examinations were made independently by two malaria microscopists, with discrepancies resolved by a senior microscopist who ensured quality control

END.

Attachment

Submitted filename: Reviewer.doc

Click here for additional data file. (37.5KB, doc)

Decision Letter 2

Luzia H Carvalho

8 Jan 2023

PONE-D-22-24029R2Prevalence Of Asymptomatic Malaria Infections By Microscopy And Its Determinants Among Residents of Ido-Ekiti, Southwestern NigeriaPLOS ONE

Dear Dr.  Bello,

Thank you for submitting your manuscript to PLoS ONE. ​After careful consideration, we feel that your manuscript will likely be suitable for publication if the authors revise it to address specific points raised now by the reviewer. According to the reviewer, there are some specific areas where further improvements would be of substantial benefit to the readers.   For your guidance, a copy of the reviewer’s comments was included below.   Please submit your revised manuscript by January 20. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Luzia H Carvalho, Ph.D.

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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Reviewer #1: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

**********

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PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Authors have addressed the previous concerns well. But, here are additional points to be addressed and included to make manuscript more plausible before publication.

Minor comments:

Line 1: Asymptomatic Malaria Infections (remove s)

Line27: Asymptomatic Malaria Infections (remove s)

Line 60-61: … clinical immunity which is only partially develops … (remove” which is”)

Line 70: Also, the use of…. (Remove also and write as “The use of…)

Line 104- 107:

Source population: This comprised all adult individuals who were residents in Ido-Ekiti, and who presented for the annual free health programs organised by the society of family physicians of Nigeria.

Study population: The study population comprised apparently healthy individuals aged 40 years and above.

Line 108-111: Consented apparently healthy individuals …dizziness, joint pain, anorexia and malaise were included in the study.

Line 112-14: Individuals who were …conduct of this study were excluded.

Line 188: Italicize “Plasmodium”

**********

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Reviewer #1: No

**********

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Decision Letter 3

Luzia H Carvalho

12 Jan 2023

Prevalence Of Asymptomatic Malaria Infection By Microscopy And Its Determinants Among Residents of Ido-Ekiti, Southwestern Nigeria

PONE-D-22-24029R3

Dear Dr.Bello,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Luzia H Carvalho, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Acceptance letter

Luzia H Carvalho

3 Feb 2023

PONE-D-22-24029R3

Prevalence Of Asymptomatic Malaria Infection By Microscopy And Its Determinants Among Residents of Ido-Ekiti, Southwestern Nigeria

Dear Dr. Bello:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Luzia H Carvalho

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 File. Dryad data set.

    (PDF)

    Click here for additional data file. (595.8KB, pdf)
    S1 Data. ASM data.

    (XLSX)

    Click here for additional data file. (25.9KB, xlsx)
    Attachment

    Submitted filename: Review comments.docx

    Click here for additional data file. (22.1KB, docx)
    Attachment

    Submitted filename: Response to Reviewers_1.doc

    Click here for additional data file. (67.5KB, doc)
    Attachment

    Submitted filename: Reviewer.doc

    Click here for additional data file. (37.5KB, doc)
    Attachment

    Submitted filename: Reviewers_1.doc

    Click here for additional data file. (36KB, doc)

    Data Availability Statement

    The dataset is in the Dryad repository and can be accessed with the following DOI: https://doi.org/10.5061/dryad.gqnk98ssx.

    Articles from PLOS ONE are provided here courtesy of PLOS

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