Persistence of soil-transmitted helminth infections among school-age children after multiple rounds of mass drug administration in Machame Narumu, Hai District, north-eastern Tanzania

Abstract

Background

All districts in Tanzania Mainland are endemic for soil-transmitted helminth (STH) infections, and have implemented at least five rounds of preventive chemotherapy targeting school-age children (SAC) in primary schools. However, there is limited information on the prevalence of STH infections in many parts of the country. Therefore, the present study was carried out to determine the prevalence and factors associated with STH infections among 5 to 14-year-old in primary schools in Machame Narumu, Hai District, north-eastern Tanzania.

Methods

A school-based cross-sectional study was conducted between May and June 2022. A two-stage random sampling method was used where one ward out of ten wards and four out of five primary schools were selected at stage one by simple random sampling technique During stage two sampling, the pupils from each of the four selected schools were stratified by their classes, then randomly selected based on the probability-proportional-to-size (PPS) method. A structured questionnaire was used to collect information on socio-demographic information and risk factors for STH infections from each participant. Stool samples were examined under the microscope following formol-ether concentration for the detection of helminth eggs. Data were analyzed using STATA Corp Software version 16.0. Logistic regression was employed to assess factors associated with STH infections among school-age children in primary schools, Hai District. Prevalence of STH infections was obtained by dividing the number of children who were infected with STH by the total number of children who participated in the study. A p-value < 0.05 was considered statistically significant.

Results

The overall prevalence of STH infections was 26.6% (95% CI: 22.3%-31.4%), relatively higher than the national prevalence of 8.4% that was reported about 9 years ago. Trichuris trichiura was the most prevalent, with the prevalence of 10.2% (95% CI: 7.3%-13.7%), followed by Ascaris lumbricoides, 8.9% (95% CI: 6.2%-12.2%), and hookworms, 0.5% (95% CI: 0.1%-1.9%). However, multiple infections were also observed where children were infected by more than one roundworm species. Factors that were significantly associated with STH infections among SAC were age(AOR = 1.21, 95% CI: 1.03–1.42, p = 0.019), sex (AOR = 0.52, 95% CI: 0.29–0.92, p = 0.038), use of spring water (AOR = 0.41, 95% CI: 0.19–0.86, p = 0.86), and information about STH infections (AOR = 2.14, 95% CI: 1.01–4.53, p = 0.046).

Conclusion

Despite annual mass drug administration, STH infections remain a public health concern among school children in the study area, with moderate prevalence relative to the World Health Organization (WHO) thresholds of 20% to 50% prevalence. This calls for an integrated approach to include other interventions such as health and hygiene education, and programs for improving sanitation in the study area. This is the first report of STH infections in the Kilimanjaro region.

Clinical trial number

Not applicable.

Background

Soil-transmitted helminth (STH) infections are among the most common and widespread parasitic diseases affecting humans, especially in low- and middle-income countries (LMICs) with poor sanitation and hygiene conditions [1, 2]. They are among the most common Neglected Tropical Diseases (NTDs) [3], caused by different species of intestinal worms, such as roundworms (Ascaris lumbricoides), whipworms (Trichuris trichiura), and hookworms (Necator americanus and Ancylostoma duodenale) [4]. Although Soil-transmitted helminthiasis affects all age groups, school-age children are most vulnerable and are at higher risk of getting an infection [5, 6]. Among the infected population, over 260 million are pre-school-age children (PSC), 654 million are school-age children (SAC), 108 million are adolescent girls, and 138.8 million are pregnant and lactating women who live in areas where the parasites are intensively transmitted. and need treatment and preventive interventions [1, 7, 8].

More than 89 million children in Africa are estimated to be infected with soil-transmitted helminths [9–11]. Tanzania is among LMICs where climate, rural life style, and socio-economic status are main risk factors for STH infections in school children [12]. The national prevalence of STH infections was 8.4% in 2016 [13]. However, there is considerable geographical variation in the prevalence and intensity of STH infections across different regions and districts in Tanzania, depending on the local environmental, socio-economic, and epidemiological factors [14]. The prevalence of STH infections varies from one epidemiological setting to another with a range of 2% to 40%, with school-age children accounting for the highest burden of STH infections [14].

The main strategy for controlling STH infections is preventive chemotherapy, which involves the large-scale and periodic distribution of anthelmintic drugs (mainly albendazole or mebendazole). The drugs are distributed to at-risk populations, especially PSC and SAC to reduce the worm burden and prevent morbidity [15]. Achieving and maintaining elimination of STH morbidity in pre-SACand SAC is among the WHO targets to be achieved by 2030 [16]. According to the WHO [16], morbidity due to STH infections was eliminated in all countries in which PC was implemented for more than 5 years and 70% of the endemic countries were expected to eliminate STH morbidity between 2018 and 2023 [16]. However, sustainable control of STH infections is inconceivable without improvements in sanitation [16]. Therefore, an integrated approach that combines preventive chemotherapy with other interventions, such as improving WASH facilities, promoting health education and behavior change, enhancing food security and dietary diversity, and integrating STH control with other NTDs control, is recommended to achieve sustainable and long-term impact on STH infections and their associated outcomes [17]. In 2021/22, all 184 District Councils had conducted more than 5 rounds of MDA with a coverage more than 80% [18]. However, only 30 Councils (16.3%) had completed mapping of STH and determined STH endemic areas and the population at risk. In addition, only 30 Councils (16.3%) had conducted first Prevalence Evaluation activities after at least 5 rounds of MDA.

Therefore, information concerning STH infections is scarce for most of Tanzania, especially in the northern and central regions of Tanzania, including Kilimanjaro, Arusha, Manyara, Singida and Dodoma. Most of the information has been documented in Pemba Island, regions along the coast, in northwestern Tanzania (Lake zone) [19]. Few studies have documented information regarding prevalence of STH infections in the southern parts [5, 20, 21, 22], and western parts of the country [5].

A recent study by Eltantawy et al. (2021) [7] suggests that STH infections are still very common among school children in Ngorongoro Conservation Area in Arusha region, northern Tanzania. In another study by Lukambagire et al. (2015) [23], human fascioliasis (was reported in the suburbs of Arusha city, where an agricultural system including animal rearing and vegetable cultivation, and drinking of untreated water from natural streams, favors transmission.

The objective of the study was to determine the prevalence and factors associated with STH infections among 5 to 14-year-olds in Machame Narumu ward in Hai District, Kilimanjaro Region, north-eastern Tanzania. The present study provides information about the prevalence of STH in the Hai District following several national rounds of school-based deworming, addressing a critical surveillance gap in Kilimanjaro Region where no recent STH data exist, unlike other Tanzanian regions. It offers new evidence on infection persistence and the effectiveness of repeated MDA in sustaining STH control.

Methods

Study design and study site

From June 2022 to August 2022, a school-based cross-sectional study was carried out among primary school children to determine the prevalence and risk factors associated with STH infections. The study was conducted in the Hai District, one of the seven districts of the Kilimanjaro region of Tanzania, located at 3°24′30.24″S 37°10′7.32″E (Fig. 1).

Fig. 1.

Map of Tanzania showing the location of the study area, the Hai District

The Hai District has 10 wards which cover an area of about 1,217 km², located at an altitude of 1,388 m above sea level. According to the 2022 census, the population of the Hai District was 240,999 and according to the projected population from 2012, the total SAC for the Hai District Council was 50, 136 and the number of Primary Schools is 132 [18].

The Hai District is among the District Councils of Tanzania Mainland that are endemic for STH infections [23]. Both routine socio-economic activities and climatic conditions favor the transmission of soil transmitted helminths.

According to the District population census of 2002 [24], about 260,000 people were living in the coffee banana belt fetching, water from traditional irrigation furrows polluted and contaminated by animal and human waste, fertilizers and pesticides while those living in the savannahs, plain areas were depending on river water contaminated and also polluted. The District is bordered to the southwest by the Meru District of Arusha Region with few reports of helminthic infections [5, 23].

Study population, inclusion and exclusion criteria

The study population was primary school children between 5 and 14 years old in Hai District, north-eastern Tanzania. Children whose parents/guardians were willing and consented to participate in the study and living in the study area for at least three months were included in the study. The three months are based on the prepatent periods of the common soil-transmitted helminths, hence possibility of finding eggs in faeces following infection with soil-transmitted helminths. Children who were under anthelminthic medication two weeks prior to the study period, children who were seriously ill, and those who did not attend school for any reason during the period of the study were excluded from the study.

Sampling and sample size estimation

In order to generate accurate prevalence estimates, a two-stage random sampling method was used at the district level to select participating schools and children for the study, as previously described by Cha et al. (2017) [25]. Stage one sampling involved the random selection of one ward (Machame Narumu) and four out of five primary schools at the ward level, using simple random sampling through the balloting method.

The four primary schools that were randomly selected include Narumu Tela Primary School, Narumu Primary School, Usari Primary School, and Orori Primary School. During stage two sampling, the pupils from each of the four selected schools were stratified by their classes, from Class One to Class Seven. The number of school children selected from each grade was determined by the probability-proportional-to-size (PPS) method. An attempt was made to sample equal numbers of boys and girls from each grade. Upon selecting the schools, about a hundred pupils were sampled from each school.

The minimum number of Primary School children was estimated by using the following formula:

Where by N = Sample size

Z² = confidence interval (95%=1.96)

P = prevalence of Northern-Western Tanzania is of 37% Bukindu et al.(2016) [8]. ɛ²= marginal error (5%)

By adding 10% of non-response (N = 358.19 + 35.8)

Hence, the sample size was 394.

Dependent and independent variables

In this study, dependent variable was soil-transmitted infections, that was assessed as binary outcome based on the presence or absence of at least one species of the soil-transmitted helminths detected by microscopic examination of stool samples from the participants of the study.

Independent variables were socio-demographic characteristics (age, sex, gender, grade), availability of toilet at home, type of toilet available at home, hand hygiene practice at home/school, water availability at home, knowledge on transmission, prevention and symptoms of STH infection, participation on agricultural activities at home. The KAP related questions for independent variables had two options, either Yes or No.

Data collection and laboratory procedures

A week before stool collection, parents/guardians of the selected pupils were provided with consent forms in Swahili to read and sign for their children to participate in the study. A day before the collection of stool samples, the objectives of the study were explained to the school teachers and pupils, and each pupil was asked to provide his/her assent to participate in the study. On the same day, a structured questionnaire with closed-ended questions was also administered. Only children whose parents signed the consent form, and who provided assent to participate, were qualified to respond to the questionnaire with the help of the research team and their class teachers. The next day, pupils who were eligible to participate in the study were provided with stool containers for stool sample collection. They were also provided with clean wooden applicator sticks. The containers were clean and leak-proof. Children were identified by individual codes, and their names were written separately in a notebook for precision during the return of their results. Each pupil was requested to bring his / her pea size stool sample. On delivery, the next day, using a list of names with their corresponding code numbers, children were called one after the other by name to collect the stool sample.

For an accuracy check, the number on the container was compared with the number recorded in the notebook. Only a single stool sample was collected from each study participant because of time constraints. The stool samples were stored in a plastic bag in a cool box to maintain the morphology of eggs, and transported to the medical laboratory, where most of the samples were processed on the same day. However, the samples that were not processed on the same day were preserved in 10% formalin, stored in a freezer to maintain stable microbiota of the stool samples and processed within a week. In the laboratory, each stool sample was processed using the formol-ether concentration technique followed by microscopic examination, using a 10x objective, and then turned into 40x for confirmation and identification of the organism(s) seen as described by Cheesbrough (2010) [26]. Duplicate smears (slides) were prepared from a single stool sample collected from each participant (child). Microscopic examination was done by two microscopists. However, a third person was not employed since there was no discrepancies among the two. The standard operating procedures were followed during stool collection, processing, and microscopic examination as described in the WHO bench mark aid for diagnosis of parasitic infections [27]. Identification of the parasites was based on the morphology of parasite eggs using bench mark aid for diagnosis of parasitic infections [27]. The laboratory findings were recorded in the laboratory book.

Risk factors associated with soil-transmitted helminth infections

The risk factors associated with soil-transmitted helminth infections were assessed using the Swahili structured questionnaire with closed-ended questions. It was pre-tested questionnaire that was adopted from a previous study by Mugono et al. (2014) [28], with minor modifications, where questions for the risk factors for acquiring schistosomiasis were excluded.

This was done before the collection of stool samples from the participants. Each pupil was questioned separately to avoid influence from friends. The information that was collected includes socio-demographic factors of the participants, use of toilets, water access and usage, hand washing practices, awareness of STH infections, and agricultural practices. The questionnaire was administered by well-trained interviewers to collect information on each pupil, and their responses were recorded by ticking the appropriate boxes provided.

Data management and analysis

The questionnaires were reviewed daily in the field after activities to check if there were any errors or mistakes to correct before participant left the field, then all questionnaires were collected together and counted to check if there were any missing questionnaires to avoid loss of data. Laboratory data were also checked daily for consistency and accuracy. Data were entered into an Excel spreadsheet, cleaned, and imported to the STATA Corp Software version 16.0 (STATA Corp, College Station, TX, LLC) for statistical analysis. Categorical data were summarized using frequencies and proportions. Logistic regression analysis was employed to assess the association between the independent variables and the dependent variables, and the association was expressed through the Crude Odds Ratio (COR) and Adjusted Odds Ratio (AOR). Multivariate logistic model was chosen to assess risk factors associated with STH infections. In order to get the best model that fits our data; statistical methods such as cross-tabulations (χ² test) and simple logistic regressions were used in initial stage of model assessment. The model with age as factor variable was compared to the model with age as a linear variable. The same applied to education level, both indicated that age, and education level best explain the model in linear form.

Two variables; using river and canal water as source of drinking water were combined to avoid multicollinearity because their responses were highly correlated. A p-value of less than 0.05 at 95% confidence was considered statistically significant. The Hosmer-Lemeshow goodness -of-fit test was used to assess the degree to which the model fits the observed data. A non-significant test shows that the model fits the data reasonably well.

Results

Socio-demographic characteristics

Out of 394 children who were interviewed, 383 were able to provide stool samples hence included in the study. Therefore, the response rate was high (97.2%). The analysis and results presented are based on 383 children who participated in the interview and provided stool samples.

Table 1 summarizes the demographics of 383 participants from Narumu Tela Primary School, Usari Primary School, Narumu Primary School, and Orori Primary School. The age distribution among the SAC children was not balanced where 324 out of 383 (84.6%), were from the age group of 9–14 years, and the remaining 59 (15.4%) were aged between 5 and 8 years. The study participants consisted of 176 (46%) males and 207 (54%) females. Ninety-two (92) pupils (24%), 101 pupils (26.4%), 102 pupils (26.6%), and 88 pupils (23%) were from Narumu Tela Primary School, Usari Primary School, Narumu Primary School, and Orori Primary School, respectively. Regarding the grade level, 273 pupils (71.3%) were in grades 1–4, and 110 pupils (28.7%) were in grades 5–7 (Table 1).

Table 1.

Socio-demographic characteristics of school-age children in the 4 surveyed schools in Machame Narumu, Hai district (N = 383)

Variables	Frequency (n)	Percentage (%)
Age (Years)
5–8	59	15.4
9–14	324	84.6
Gender
Male	176	46.0
Female	207	54.0
School
Narumu Tela Primary School	92	24.0
Usari Primary School	101	26.4
Narumu Primary School	102	26.6
Orori Primary School	88	23.0
Grade
1–4	273	71.3
5–7	110	28.7

Prevalence of soil-transmitted helminth infections

Overall, out of 383 stool samples that were examined, 102 were positive for at least one STH infection, thus a prevalence of STH infections of 26.6% (95% CI: 22.3%-31.4%). Out of these, 39 children (10.2%, 95% CI: 7.3%-13.7%) were infected with T. trichiura, 34 children (8.9%, 95% CI: 6.2%-12.2%) were infected with A. lumbricoides, and 2 children (0.5%, 95% CI: 0.1%-1.9%), were infected with hookworms. However, 22 children (5.7%,95% CI:3.6–8.6) were infected with both A. lumbricoides and T. trichiura, 2 children (0.5%,95% CI: 0.1% -1.9%) were infected with both A. lumbricoides and hookworms, and 2 children (0.5%, 95% CI: 0.1% -1.9%) were found infected with both A. lumbricoides, T. trichiura, and hookworms. Only 1 child (0.3%, 95% CI: 0.0% -1.4%) was found infected with both T. trichiura and hookworms, (Table 2).

Table 2.

Prevalence of soil-transmitted helminth infections among the school-age children in the four surveyed schools in Machame Narumu, Hai Dstrict (N = 383)

Helminth	Frequency (n)	Percentage Age (%)	95%CI
Trichuris trichiura	39	10,2	7.3–13.7
Ascaris lumbricoides	34	8.9	6.2–12.2
A.lumbricoides and T.trichiura	22	5.7	3.6–8.6
Hookworms	2	0.5	0.1–1.9
A.lumbricoides, T.trichiura and hookworms hookworms	2	0.5	0.1–1.9
A.lumbricoides and hookworms	2	0.5	0.1–1.9
T.trichiura and hookworms	1	0.3	0.0-1.4
Total	102	26.6	22.3–31.4

Availability and use of water for hygiene practices

The water was available from different sources, including taps, wells, rivers, rain, springs and canals. Interestingly, all participants reported to have toilets at home of which were either flushing toilets or pit latrines, and the majority of participants (86.4%) had access to tap water. The information regarding usage of water for hygiene practices is summarized in Table 3, including washing of hands before eating, and after using the toilet. Notably, only 19.1% of the participants were boiling the water for drinking.

Table 3.

Availability and use of water for hygiene practices among the school-age children in the four surveyed schools in Machame Narumu, Hai district (N = 383)

Practices	Frequency (n)	Percentage (%)
Awareness of handwashing practices
Yes	263	68.7
No	120	31.3
Washing hands before eating
Sometimes	121	31.6
Always	262	68.4
Boiling water for drinking
Yes	73	19.1
No	310	80.9
Presence of toilet/latrine at home
Yes	383	100.0
No	0	0.0
Washing hands with soap after using the toilet toilet toilet
Sometimes	268	70.0
Always	115	30.0
Usage of tap water
Yes	331	86.4
No	52	13.6
Usage of well water
Yes	24	6.3
No	359	93.7
Usage of river water
Yes	92	24.0
No	291	76.0
Usage of rainwater
Yes	73	19.1
No	310	80.9
Usage of spring water
Yes	97	25.3
No	286	74.7
Usage of canal water
Yes	217	56.7
No	166	43.3

Awareness of soil-transmitted helminth infections

The awareness of children on soil-transmitted helminth infections was generally moderate, as summarized in Table 4. Surprisingly, most of the participants (96.9%) reported having used an anthelminthic drug.

Table 4.

Awareness of soil-transmitted helminth infections among the school-age children in the four surveyed schools in Machame Narumu, Hai district (N = 383)

Variables	Frequency (n)	Percentage (%)
Ever heard about STH infections
Yes	212	55.4
No	171	44.6
Suffered from STH infections
Yes	19	5.0
No	364	95.0
Ever used an antihelminthic drug
Yes	371	96.9
No	12	3.1
Ever been educated about STH infections
Yes	64	16.7
No	319	83.3

Multivariate logistic model for the risk factors associated with STH infections

In general, the model was found to fit the data on the factors associated with STH infections in the study area. With one-year increase in age of pupils from 5 years to 14 years, the odds of infection from STHs increased significantly (AOR = 1.21, CI: 1.03%-1.42%, p = 0.019). Being a male or female was significantly associated with STHs infection, males were 48% protective from getting STH infections (AOR = 0.52, CI: 0.29%-0.92%, p = 0.038). Pupils who use pit latrines at home were 1.74 times more likely to suffer from STH infections as compared to those using flushing toilets (AOR = 1.74, CI: 1.00%-3.03%, p = 0.052).

Using spring water as a primary drinking source at home, was significantly associated with a 59% reduction of STHs infection among schoolchildren (AOR = 0.41, CI: 0.19%-0.86%, p = 0.018). The use of river or canal water for drinking was highly associated with the reduction in STHs infection (AOR = 0.39, CI: 0.19%-0.79%, p = 0.008). Pupils who had previously received education about STHs infections were found to be 2.14 times more likely to be infected with STH infections compared to those who had not received such education (AOR = 2.14, CI: 1.01%-4.53%, p = 0.046) (Table 5).

Table 5.

Multivariate logistic model for soil transmitted helminth infections among pupils in Machame Narumu, Hai district

Variables	COR	95% CI		p- value	AOR	95% CI		p- value
		Lower	Upper			Lower	Upper
Age in years	1.07	0.96	1.19	0.228	1.21	1.03	1.42	0.019*
School level	1.10	0.99	1.23	0.084	0.91	0.78	1.07	0.259
Sex
Female	1				1
Male	0.83	0.56	1.23	0.347	0.52	0.29	0.97	0.038*
Toilet type
Flushing toilet	1				1
Pit Latrine	1.56	1.03	2.37	0.035	1.74	1.00	3.03	0.052
Tap water
No	1				1
Yes	1.54	0.91	2.61	0.107	1.61	0.74	3.54	0.232
Well water
No	1				1
Yes	1.21	0.51	2.90	0.667	0.82	0.28	2.42	0.716
Rain water
No	1				1
Yes	0.98	0.59	1.65	0.943	1.25	0.60	2.59	0.555
Spring water
No	1				1
Yes	0.74	0.48	1.15	0.184	0.41	0.19	0.86	0.018*
River or canal water
No	1				1
Yes	0.74	0.49	1.12	0.152	0.39	0.19	0.79	0.008*
Boil drinking water
No	1				1
Yes	0.85	0.52	1.39	0.526	0.79	0.38	1.63	0.525
Hand wash after toilet
Always	1				1
Sometimes	1.13	0.75	1.71	0.554	1.59	0.81	3.12	0.179
Hand wash before meal
Always	1				1
Sometimes	1.73	1.09	2.74	0.019	1.97	0.91	4.26	0.084
Wear rain boots
No	1				1
Yes	0.72	0.43	1.21	0.218	0.71	0.39	1.29	0.264
Ever got education about STHs
No	1				1
Yes	1.34	0.82	2.22	0.247	2.14	1.01	4.53	0.046*

Hosmer-Lemeshow post diagnostic test for the goodness of fit: χ² = 252.6, p-value = 0.071

STHs = Soil transmitted helminths, COR = Crude Odds Ratio, AOR = Adjusted Odds Ratio, CI = Confidence Interval

*p-values were significant

Discussion

For over a decade, School-based Mass Drug Administration (MDA) has been the main strategy for preventing and controlling Soil Transmitted Helminths (STH) infections in Tanzania. However, some studies, including that of Jones et al. (2025) [5], have reported sustained STH transmission in endemic settings, suggesting that preventive chemotherapy alone may be insufficient without complementary improvements in sanitation, hygiene, and behavioral interventions [6]. The present study was carried out to determine the prevalence and factors associated with an increased risk of STH infections among school-age children (5–14 years) in Machame Narumu ward in Hai District, north-eastern Tanzania.

The findings of the present study show that STH infections remain a major public health concern among school-age children in Machame Narumu ward in Hai District, with an overall prevalence of 26.6%. This is similar to a previous study in Hoima District, Uganda [29], where the overall prevalence of STH infections among preschool-age children was 26.5%. Children were found to be infected with either Trichuris trichiura, Ascaris lumbricoides, or hookworm. Multiple infections were also observed, including A. lumbricoides and hookworms, A. lumbricoides and T. trichiura, and hookworms, and a few children were infected with A. lumbricoides, T. trichiura, and hookworms.

Although age was associated with the risk of STH infection when modeled as a continuous variable, categorical comparisons between younger (5–8 years) and older (9–14 years) children were not statistically significant. This could be due to the fact that age distribution between the two age groups (5 to 8 years), and (9 to 14 years) was not balanced. Therefore, no definitive conclusions can be drawn regarding age-specific differences in STH burden in this study. However, the age distribution between the two age groups was not balanced and this could limit age related comparisons. The reason for unbalanced age distribution could be due to the fact that in Tanzania, 7 years as the compulsory age for enrollment of a child to a school for primary education. However, the Education Act does not render a child under the age of 7 years ineligible for enrollment for primary education Tanzania.

The prevalence of STH varies with geographical distribution, climatic conditions, and socio-economic activities [15, 30]. According to the WHO classification of STH infections endemicity mapping, three categories exist in line with implementation of mass drug administration (MDA): (i) high transmission (where prevalence is > 50%), (ii) moderate transmission (where prevalence is between 20% and 50%), and (iii) low transmission (where prevalence is < 20%) [31].

The findings of the present study show that the Machame Narumu ward in the Hai District falls under moderate transmission, whereby the prevalence of STH was found to be 26.6%, despite one round of mass administration administered in the area per year. The prevalence is relatively higher than the national average of 8.4% reported by the Tanzania Ministry of Health, Community Development, Gender, Elderly and Children (MoHCDGEC) in 2016 (MoHCDGEC, 2016) [13, 16]. The moderate prevalence of STH infections may be attributed to re-infections occurring after the annual mass deworming programs. A recent study by Jones et al.(2025) [5], has reported a relatively low prevalence (< 10%) in the majority of surveyed district/town councils, including Iringa District Council (DC), Nanyamba Town Council (TC), Ruangwa DC, Tanganyika DC, and Kalambo DC. Elsewhere in the Ilemela District Council in Mwanza, the prevalence of STH infection among primary school children was found to be 18.7% [32]. However, the observed prevalence is much lower than the prevalence of previous studies that were conducted elsewhere in Jima town in Ethiopia (75.1%) [33] and Nigeria (54.8%) [34]. The differences in prevalence may in part be linked to differences in the climate, environment, and lifestyle, and the different methods for fecal analysis.

Environmental factors such as the District’s fertile volcanic soils, high rainfall, and moderate temperatures create optimal conditions for helminth egg survival and larval development. Similar environmental drivers of transmission have been reported in Ngorongoro and Sengerema Districts [7, 8, 10, 11]. Furthermore, the dependence on pit latrines, which are common in rural and peri-urban schools in Hai, was significantly associated with higher odds of infection. This is consistent with findings from Mwanza [8] and Ukara Island [26], where inadequate sanitation infrastructure was linked to elevated STH prevalence.

Behavioral factors also played a critical role. Younger children (5–8 years) were more affected, probably due to higher exposure to contaminated soil and poor hygiene practices. Poor handwashing habits, open defecation, and consumption of unwashed fruits and vegetables have been identified as behavioral risk factors in similar Tanzanian settings [31, 32]. In this study, pupils who were not always washing their hands after vising a toilet were at higher risk of acquiring STH infections than those who were always washing their hands after vising a toilet. Likewise, those who were not always washing their hands before meal were at higher risk of acquiring STH infections than those who were always washing their hands before meal. However, the associations were not statistically significant. The observed association between having received education about soil-transmitted helminths and higher odds of infection should be interpreted with caution. This finding does not suggest that health education increases the risk of STH infection. rather, it is likely.

The association between knowledge of STH infections and higher infection rates observed in this study reflects reverse causality, whereby children who had previously experienced STH infection or related symptoms were more likely to receive targeted education through school health programs or clinical encounters. In addition, self-reported exposure to health education may be subject to recall bias. Similar associations have been reported in cross-sectional studies where exposure and outcome are assessed simultaneously in Ethiopia (75.1%) [33] and Nigeria (54.8%) [34] but remains higher than that reported in Ilemela District (18.7%) [29]. These differences may be attributed to variations in local sanitation, community engagement in health education, and intensity of MDA campaigns. According to a systematic review by Agrawal et al. (2024) [6], residual STH transmission persists where MDA coverage, sanitation, and hygiene promotion are not synergistically implemented in low- and middle-income countries.

In the study area, spring water sources are often protected, gravity-fed, and less exposed to surface contamination compared with rivers or canals, which may explain the reduced odds of infection. However, the association may be confounded by unmeasured factors such as household location, altitude, or socio-economic status. Surprisingly, the use of river or canal water as the source of water at home, decreased the odds of STH infection. This could be explained by the location of the Machame Narumu ward. The ward is located in the highlands where contamination is less. The rivers originate from Mount Kilimanjaro and the canals originate from those rivers that are less contaminated.

The WHO 2030 NTD Roadmap aims to reduce the global prevalence of STH infections to below 2% moderate-to-heavy intensity infections among at-risk populations [16]. The persistence of moderate transmission levels in the study area indicates that Tanzania may need to intensify integrated control efforts combining preventive chemotherapy with targeted health education, improved water, sanitation, and hygiene (WASH) interventions, and regular surveillance. Indeed, the transmission cycle of soil-transmitted helminthiases and other NTDs cannot be broken by treatment alone, and improvements in water, sanitation and hygiene (WASH) are critical for achieving control and elimination of these diseases [35, 36].

The continued prevalence above the WHO elimination threshold underscores the need for district-level operational research to evaluate compliance, reinfection rates, and community perceptions toward MDA campaigns. Overall, the findings emphasize that while school-based deworming remains an essential intervention, sustainable control of STH in Hai District requires a multisectoral approach addressing both biomedical and socio-environmental determinants.

Strengthening intersectoral collaboration between the health, education, and water sectors, alongside scaling up community-led sanitation programs, is critical to achieving the WHO 2030 elimination targets in Tanzania.

Limitations of the study

The present study was a cross-sectional study to determine the prevalence of STH infections after several rounds of MDA in the area. However, we did not have the baseline prevalence of the STH infections that would be useful in the measurement and evaluation of the impact of mass drug administration in the study area. In this study, only one ward was selected out of the 10 wards of Hai District due to financial constraints, therefore the findings may not be generalized for the whole Hai District. Formol- ether concentration method was employed in this study, which is less sensitive compared to Kato-Katz, the most frequently used technique in the field. Therefore, we might have missed the light infections hence underestimation of the actual prevalence of the STH infections in the study area. Only one fecal sample was collected instead of three consecutive time samples due to time constraints. Moreover, we did not calculate the intensity of soil-transmitted helminth infections in the study population. Some information that was collected through a structured questionnaire including awareness of soil-transmitted helminth infections seem to be subjected to recall bias by the pupils. The age distribution between the two age groups (5 to 8 years), and (9 to 14 years) was not balanced and this could limit age related comparisons. Lastly, clustering by grades or classes was not accounted for in the analysis.

Conclusions

The findings of this study show persistent STH infections after multiple round of mass drug administration in the Hai District, highlighting the need for integrated control strategies. The prevalence of soil-transmitted helminths among school children in the study area was found to be moderate. Surveillance should be embedded within school-based health programs to enable continuous monitoring. WASH and behavior change components must be strengthened to reduce reinfection, and biannual deworming should be considered in the Hai District. Target treatment coverage should be at least 75% for all age groups from two years old, including pregnant women (after the first trimester) and lactating women. These actions will support Tanzania’s progress toward the WHO 2030 STH elimination targets.

Abbreviations

AOR

Adjusted Odds Ratio

CI

Confidence interval

COR

Crude Odds Ratio

KAP

Knowledge Attitudes and Practces

MDA

Mass drug administration

NTDs

Neglected tropical diseases

PSC

Preschool children

SAC

School-age children

SPSS

Statistical Package for Social Sciences

STH

Soil Transmitted Helminth

WASH

Water, sanitation, and hygiene

Author contributions

FM and JM conceived and designed the study. analyzed the data, wrote the first draft of the manuscript. RK prepared the map of Tanzania showing the location of the study site and revised subsequent versions of the manuscript. CN and BN participated in data collection and revised the first draft of the manuscript. FT participated in data analysis. All authors have read and approved the manuscript.

Funding

No specific funding was received for this study.

Data availability

All data generated or analyzed during this study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

Our study was conducted in accordance with the Declaration of Helsinki. Ethical approval for the study was received from the KCMC University Research Ethics Review Committee (KURERC) (Ethical clearance certificate No. UG 03/2022). Permission to conduct research in schools in Hai District was sought from the District and Division administrative authorities. Before study initiation, Kiswahili-translated informed consent was obtained from the parents or guardians (children’s primary caregivers) for the children to participate in the study, and assent to participate in the study was sought from the children. Confidentiality was maintained where participants were assigned unique identification numbers instead of their names. The authors declare that they have no competing interests.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.