Assessment of the Prevalence of Soil-Transmitted Helminth Infections and Associated Risk Factors among School-Aged Children in a Flood-Affected Area of Northeast India

ABSTRACT.

Soil-transmitted helminthiasis is a major disease burden in developing countries, with a considerable share borne by India. Currently, the principal strategy of the World Health Organization for the control of soil-transmitted helminths (STHs) is mass deworming in the high-risk population based on the prevalence and intensity of infection in a region. However, the disease load of STH remains unknown in many regions. A cross-sectional study was conducted in 2017 among children in the age group of 5–13 years in Barpeta, Assam, to ascertain the prevalence of STH infection in school-aged children and its probable risk factors. Socio-demographic and epidemiologic data were gathered using a piloted questionnaire. Geohelminths were identified by the Kato–Katz method. Association with probable risk-factors was analyzed by binomial logistic regression. Overall, 16.3% [95% confidence interval (CI) = 12.9–19.8] of children were found to be infected with one or more of the three STHs. Ascaris, hookworm, and Trichuris infections were observed in 9.4%, 7.4%, and 5.3%, respectively. The strongest predictors for the presence of any STH with multivariable analysis were open defecation (habitual or occasional), lack of proper handwashing, living in homes affected by flood, and age group of 8–10 years. The availability of proper handwashing stations in schools was found to be protective against Trichuris. Awareness among the people regarding sanitation and personal hygiene, particularly in the post-flood scenario, is imperative for sustainable control of STH infections. Preventive deworming should be continued; however, the time and frequency must be adjusted according to the prevailing climatic conditions in the region under study.

INTRODUCTION

The most common species of parasites that infect human beings worldwide are roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworms (Ancylostoma duodenale and Necator americanus).¹ They respond to similar anti-helminthic treatments and are diagnosed by the same laboratory methods; these are normally addressed as a group called “soil-transmitted helminths” (STHs). Transmission of STH infections occurs via ingestion of eggs passed by the infected people in their stools, thereby contaminating soil and water sources or by penetration of larvae hatched from the eggs. Therefore, it is highly prevalent in developing countries with poor sanitation and hygiene. Tropical climate and excessive rainfall further favor the spread of these infections.^1–3

Soil-transmitted helminthiasis has been listed among the 17 neglected tropical diseases (NTDs) by the World Health Organization (WHO).² In 2001, the World Health Assembly endorsed “regular treatment of high-risk groups” as the best means of reducing morbidity and mortality, and they urged the endemic countries to attain by 2010 a minimum target of regular administration of chemotherapy to at least 75%, and up to 100%, of all school-aged children (SAC) at risk of morbidity.⁴ The WHO recommends mass drug administration (MDA) for STH twice yearly in high-risk communities (prevalence > 50%) and annually in moderate-risk communities (prevalence 20–50%).^5,6 During the decade 2001–2010, STH control focused almost exclusively on preventive chemotherapy (PC), targeting SAC through the education sector. However, it has been increasingly recognized that for control to be both effective and sustainable, it is necessary to adopt an integrated approach. By the second decade of the millennium, other recommendations and strategies were incorporated, but major challenges in attaining the target of controlling and eliminating STHs remained.⁶ Periodic de-worming coupled with health awareness, improvement of water supply, better sanitation practices, and behavioral changes, are essential to interrupt the chain of transmission.^6,7

About 1.45 billion people are estimated to be infected with STHs worldwide, with children being the most affected group. Nearly 70% of the cases are found in Asia.⁸ India alone has the highest burden of the disease globally and harbors more than one-fourth (27%) of the total pre-SAC and SAC in need of deworming.^6,9 The prevalence of STHs infection varies widely from region to region in India, with Ascaris lumbricoides infection ranging from 0.6–91%, Trichuris trichiura infection ranging from 0.7–72%, and hookworm infection ranging from 0.02% to 52%.¹⁰ The tropical rainforests of upper Assam are highly endemic for geohelminths, and there is evidence for a high level of STH infection.^11–13 However, there is a gap in the knowledge regarding the actual burden of STH infection in lower Assam. Moreover, the Barpeta district is prone to flooding every year, and to the best of our knowledge, no research work has been done to check the role of flooding in geohelminth infections.

The objective of this study was to estimate the prevalence of STH among SAC in and around the Barpeta town Assam and to identify its association with probable risk factors and preventive chemotherapy.

MATERIAL AND METHODS

Ethical considerations.

The study protocol was submitted to the Institutional Ethics Committee of Fakhruddin Ali Ahmed Medical College and Hospital (FAAMCH), a tertiary care teaching hospital; and approval was granted (No. FAAMC&H/128/Pt./2017/3484, dated June 8, 2017). The heads of the four schools were informed in writing 3 days prior to the study, and their approvals were obtained. Because the study subjects were minors, written informed consent was obtained from the class teachers/parents. Children who were diagnosed with helminthiasis were treated with a full course of Albendazole.

Study design and setting.

This is a cross-sectional study conducted in Barpeta town of Assam in northeast India between June and August 2017. Barpeta is an agro-based district, situated at an altitude of 35 meters above sea level, and it contains numerous scattered water bodies. Many tributaries and sub-tributaries of the river Brahmaputra flow through and around this area. It receives moderate-to-heavy rainfall for prolonged periods from June to September every year, with an annual average of 2,694.0 cm,¹⁴ which leads to waterlogging in many parts within the town. Many low-lying areas on either bank of the river are affected by floods every year during monsoons. Tropical hot and humid climate (average temperature of 31.7°C–31.9°C during June–July) prevails in this area, which is rich in biodiversity.

Study population and sample-size estimation.

Four schools were selected randomly from in and around Barpeta town. None of the selected schools had undergone preventive deworming in the preceding 3 months, i.e., March–May 2017. The children were selected on a class-by-class basis and were spread equally according to year groups and gender. Children younger than 5 years or older than 13 years were excluded even if they were enrolled at the school.

The sample size was calculated using the formula n = z²P(1-P)/d² (n = sample size; confidence level at 95% (standard value of 1.96); P = expected prevalence of the disease in the particular area; d = precision).¹⁵ As per the National Center for Disease Control (2016), the prevalence of STH in Assam was estimated to be 50%¹⁶; hence, P was taken to be 0.5 (50%). Taking 5% as absolute precision, the sample size was calculated to be 384. To account for refusals or nonresponses, the sample size was increased by 10% to a final sample size of 422.

Data and sample collection.

Data were collected from each school over a period of 6 days. On Day 1, children in the age group of 5–13 years were selected. A pre-designed, pre-tested (piloted in a small group) short questionnaire prepared in two local vernacular languages was given to each child to collect information about socio-demographic details, presence of toilet facilities and their use, handwashing practices, house type, flood-affected status, and history of deworming in the last (one) year. A pilot test was done to validate the survey instruments with 30 students before its implementation. Two of the researchers spoke to the teachers and parents, instructed the parents to fill the questionnaire, and answered all their queries. The parents were assured that if the children were found to be infected, they would be reported and adequately treated. The condition of toilet/open space used by the students in the schools was assessed by subjective evaluation. Any handwashing facility in the school was also observed and recorded. On Day 2, the collected questionnaires were checked and the children who submitted a filled-in questionnaire were included in the study. Each child was given three dry, clean, leakproof, screw-capped containers with their names written on the label outside. Instruction was given to the children and their parents to collect early morning stool cleanly in the container and to record the time on the label. The participating schoolchildren were asked to submit three stool specimens on consecutive days. From Day 3 onwards, properly collected and labeled stool samples were received by trained technicians. This activity continued up to Day 6, until three early morning stool samples were submitted by each enrolled student. The samples were then transported to the microbiology laboratory of FAAMCH, maintaining proper hygiene and biosafety measures. Students who failed to provide three properly labeled early morning stool samples were excluded.

Laboratory methods.

The samples were processed in the laboratory of the Department of Microbiology immediately on receipt. Macroscopic examination of the stool was performed to observe its consistency, presence of blood and mucus, or any parasitic elements. Within two hours of collection, a single thick Kato–Katz smear was prepared on a slide for each sample using a standard template with a hole diameter of 6 mm and depth of 1.5 mm, holding 41.7 mg of feces. Within 30–60 min, the slides were examined under both low (10x) and high power (40x) objective lenses of a light microscope. To eliminate observer bias, the slides were examined individually by two researchers, and quality control of each negative slide was performed and confirmed by a senior microbiologist. Ova of parasites were identified based on their characteristic morphology and bile staining properties. The number of helminth eggs, if present, was counted and recorded. The slides were re-examined after 2 hours. This process was repeated for the second and third samples on the subsequent days.

As per WHO guidelines, we identified three classes of infection intensity, namely light, moderate, and heavy, depending on the egg count per gram (EPG). For Ascaris, the infections were categorized as light, moderate, and heavy intensity if the counts were 1–4,999 EPG, 5,000–49,999 EPG, and > 50,000, respectively. Similarly, for Trichuris, 1–999 EPG, 1,000–9,999 EPG, and > 10,000 EPG were classified as light, moderate, and heavy intensity infection, respectively. The comparable counts for hookworms were 1–1,999 EPG, 2,000–3,999 EPG, and > 4,000 EPG, respectively.¹⁶

Data management and statistical analysis.

A MS Office Excel spreadsheet 2010 (Microsoft) was used to enter questionnaire data and create tables and graphs. The data were checked for errors, missing values, and extreme values or outliers. QGIS (v3.14) was used to create a map using prevalence statistics. The data were further analyzed with the help of a standard software package (SPSS v23.0; Chicago, IL). Descriptive statistics (frequency, cumulative frequency, percentages, means, and standard deviations) were used to characterize the study population. Point prevalence with 95% confidence intervals (95% CI) was calculated for overall STH infections and for each STH species. Similarly, point prevalence with 95% CI was calculated for mixed parasitism (i.e., infections involving more than one species). The data were further analyzed for potential associated factors by univariable and multivariable analyses. Pearson’s Chi-square test was applied to compare the categorical variables. A stepwise conditional binomial logistic regression analysis was performed to control for the effects of confounding variables and to identify the independent associated factors. Binary outcome variables (dependent variable) of “any STH infection” and individual infection by the three species (i.e., “Ascaris lumbricoides,” “Hookworm,” and “Trichuris trichiura”) were assessed separately for a set of independent variables initially by univariable logistic regression. Socio-demographic indicators such as age group, gender, religion, and place of residence; putative risk-factors such as handwashing, site of defecation, dwelling places ravaged by flood, type of flooring, absence of handwashing station at school; and previous history of deworming treatment were checked for association. All the variables with a P value of < 0.25 at the univariable level were included in the multivariable logit model by stepwise forward selection method. Odds ratios (OR) and 95% CI were estimated for all the outcome variables in both univariable and multivariable analyses. All P values were two-tailed, and a P value of < 0.05 was considered statistically significant.

RESULTS

Study participation and population characteristics.

A total of 560 students between the ages of 5 and 13 years (belonging to four schools) were selected, out of which, 489 students submitted a completely filled-in questionnaire. Among them, 435 (77.68% compliance) produced three viable consecutive fecal samples and were finally enrolled in the study (Figure 1). Of the included participants, 238 (54.7%) were boys and 197 (45.3%) were girls. The mean age of the study population was 8.6 years [standard deviation (SD) ± 2.47 years]. The age and gender distributions among the selected schools were comparable. It was noted that 37.7% (N = 164) were Hindus, while the rest (62.3%, N = 271) were Muslims (Table 1). From the four schools of Rangapani (School 1), Muslimpatty (School 2), Jotinagar (School 3), and Baradi (School 4), 79, 137, 130, and 89 children, respectively, were enrolled (Table 2).

Figure 1.

Flow chart detailing the study recruitment process. The investigation was conducted in 2017, and the study population comprised of children enrolled in four schools located in and around Barpeta Town, Assam.

Table 1.

Structural, social, and behavioral characteristics of school children enrolled in the study (N = 435)

Characteristics		No. of cases	Percentage
Age (in years)*	5	54	12.4
	6	60	13.8
	7	41	9.4
	8	58	13.3
	9	56	12.9
	10	54	12.4
	11	39	9.0
	12	41	9.4
	13	32	7.4
Gender	Male	238	54.7
	Female	197	45.3
Religion	Hindu	164	37.7
	Muslim	271	62.3
	Others	0	0
Defecation practice†	Sanitary latrine	109	25.1
	Open air	114	26.2
	Both	212	48.7
Habit of washing hands with soap‡	Always	126	29.0
	Never	86	19.8
	Sometimes	223	51.2
Home affected by flood (at least once in last year)§	Yes	144	33.1
	No	291	66.9
Type of flooring	Kaccha partial/complete	310	71.3
	Concrete	125	28.7
Deworming in the last year	Yes	277	63.7
	No	93	21.4
	Doubtful¶	65	14.9
Hand washing station at school‖	Yes	155	35.6
	No	280	64.4

^*The number denotes the completed age in years up to 1 day less than the succeeding year.

^†Variables (sanitary latrine, open air, both) are created from questions in the questionnaire pertaining to frequency of use of backyard, open field, river, jungle, or sanitary latrine for defecation.

^‡Variables (always, never, sometimes) are created from choices of “soap”, “only water”, and “others–specify” in the question regarding the hand hygiene practices after defecation.

^§Variable “yes” is created for flood water entering inside rooms of house or front/back yard at least once in the last year.

^‖Variable “yes” implies presence of tap/tube well water inside the campus and availability of soap near it.

^¶“Doubtful” is created for those children who are not sure of taking any anti-helminthic medication in the last year and who left that question blank on the questionnaire.

Table 2.

Distribution of soil-transmitted helminth infections among children in the four surveyed schools

	Number and (%)† of children found positive per school				Overall infected (N = 435), n (%)* [95% CI]‡
STHs	School 1 (N = 79)	School 2 (N = 137)	School 3 (N = 130)	School 4 (N = 89)
Total single infestation	17 (21.52)	18 (13.14)	7 (5.38)	8 (8.99)	50 (11.5)
					[8.5–14.5]
Ascaris lumbricoides	6 (7.6)	7 (5.1)	2 (1.5)	5 (5.6)	20 (4.6)
Hookworm	11 (13.9)	6 (4.6)	2 (1.5)	2 (2.3)	21 (4.8)
Trichuris trichiura	0	5 (3.6)	3 (2.3)	1 (1.1)	9 (1.8)
Total double infestation	4 (5.1)	4 (3.1)	8 (6.2)	1 (1.1)	17 (3.9)
					[2.1–5.7]
Ascaris + hookworm	2 (2.5)	2 (1.5)	3 (2.3)	0	7 (1.6)
Ascaris + Trichuris	2 (2.5)	2 (1.5)	5 (3.8)	1 (1.1)	10 (2.3)
Hookworm + Trichuris	0	0	0	0	0
Total triple infestation Ascaris + hookworm + Trichuris	2 (2.5)	2 (1.5)	0	0	4 (0.9)
					[0.02–1.8]
Any STH§	22 (27.8)	24 (17.5)	16 (12.3)	9 (10.1)	71 (16.3)
					[12.9–19.8]
Ascaris total	12 (15.2)	13 (9.5)	10 (7.7)	6 (6.7)	41 (9.4)
					[6.7–12.2]
Hookworm total	14 (17.7)	10 (7.3)	6 (4.6)	2 (2.2)	32 (7.4)
					[4.9–9.8]
Trichuris total	4 (5.1)	9 (6.6)	8 (9.2)	2 (2.2)	23 (5.3)
					[3.9–7.4]

CI = confidence interval.

^*Denominator for calculating percentage is the overall students enrolled in the study N = 435.

^†Denominator for calculating percentage is the number of students enrolled from each school.

^‡95% confidence interval calculated using normal approximation to the binomial calculation.

^§Refers to number of children positive for at least one species of soil-transmitted helminths.

Soil-transmitted helminth infection findings.

Table 2 shows the distribution of STH infections among the children in the four surveyed schools. (For prevalence, see Figure 2.) The overall prevalence of STHs, defined as the presence of one or more helminths upon the examination of three consecutive stool samples and applying Kato–Katz methods, was found to be 16.3% [95% CI = 12.9–19.8]. The prevalence of single infection was observed to be 11.5% [95% CI = 8.5–14.5] and that of double and triple infections was found to be 3.9% [95% CI = 2.1–5.7] and 0.9% [95% CI = 0.02–1.8], respectively (Figure 3). Ascaris lumbricoides was discerned to be the most prevalent helminth at N = 41, 9.4% [95% CI = 6.7–12.2], which was followed by hookworm at N = 32, 7.4% [95% CI = 4.90–9.81], and Trichuris trichiura at N = 23, 5.3% [95% CI = 3.18–7.39]. Out of the four areas surveyed, children belonging to School 1 had maximum STH prevalence at 27.8% [95% CI = 18.0–37.7], followed by Schools 2, 3, and 4, with a prevalence of 17.5% [95% CI = 11.2–23.9], 12.3% [95% CI = 6.7–17.9], and 10.1% [95% CI = 3.8–16.4], respectively. Supplemental Table 1 shows the prevalence of individual species in different risk groups and other socio-demographic characteristics of participants.

Figure 2.

Prevalence of soil-transmitted helminths in the four schools of Barpeta under survey. This figure appears in color at www.ajtmh.org.

Figure 3.

The proportion of study population with single and mixed STH infection.

The observed average Fecal Egg Count (FEC) in eggs count per gram (EPG) were 922.7, 197.7, and 62.7 for Ascaris, Trichuris, and hookworm, respectively. Most children had low intensity infection (N = 63, 88.7%). Only 11.3% (N = 8) of the children presented with moderate intensity infection. No heavy infection was found among the enrolled children.

Personal hygiene and conditions at home and school.

Table 3 describes the personal hygiene habits and prevailing sanitation at home and school of the enrolled students. Overall, 26.2% (N = 114) of children did not have access to a sanitary latrine at home and defecated openly in the backyard, open fields, or a nearby jungle/river. The remaining 73.8% (N = 321) had access to sanitary latrines either individually in their house or jointly owned by a few families. However, most (N = 212) of them (i.e., 48.7% of all the children), despite having access to toilet, reported that they indulged in the practice of open defecation and used toilets only occasionally. Only one-fourth (25.1%) of the children always used the toilet. Post defecation hand-hygiene practice with soap and water was always followed by 29.0% of them, while 19.8% never used soap. More than half of the students (51.2%) reported the occasional use of soap with other concomitant practices, such as handwashing with water only or rubbing their hands in the soil.

Table 3.

Univariate analysis of socio-demographic and other factors associated with STH infections

		Any STH†			Ascaris lumbricoides			Hookworms			Trichuris trichiura
Characteristics	N	% inf	OR (95% CI)	sig.	% inf	OR (95% CI)	sig.	% inf	OR (95% CI)	sig.	% inf	OR (95% CI)	sig.
Age category*
5–7 years	157	14.1	ref.		7.0	ref.		5.7	ref.		4.5	ref.
8–10 years	167	23.4	2.1 (1.1–3.7)	0.015	13.8	2.1 (1.0–4.5)	0.050	9.6	1.7 (0.7–4.1)	0.199	7.8	1.8 (0.7–4.6)	0.219
11–13 years	111	9.1	0.8 (0.4–1.8)	0.632	6.3	0.9 (0.3–2.4)	0.822	6.3	1.1 (0.4–3.1)	0.845	2.7	0.6 (0.2–2.8)	0.460
Gender
Male	238	16.8	ref.		9.7	ref.		7.1	ref.		5.0	ref.
Female	197	15.7	0.9 (0.5–1.5)	0.764	9.1	0.9 (0.5–1.8)	0.852	7.6	1.1 (0.5–2.2)	0.851	5.6	1.1 (0.5–2.6)	0.802
Religion
Hindu	164	16.5	ref.		9.8	ref.		6.1	ref.		6.1	ref.
Muslim	271	16.2	1.0 (0.6–1.7)	0.950	9.2	0.9 (0.5–1.8)	0.854	8.1	1.3 (0.6–2.9)	0.436	4.8	0.8 (0.3–1.8)	0.558
Place of residence
School 4	89	10.1	ref.		6.7	ref.		2.2	ref.		2.2	ref.
School 1	79	27.8	3.4 (1.5–8.0)	0.004	15.2	2.5 (0.9–7.1)	0.085	17.7	9.4 (2.1–42.7)	0.004	5.1	2.4 (0.4–13.2)	0.339
School 2	137	17.5	1.9 (0.8–4.3)	0.128	9.5	1.5 (0.9–4.0)	0.469	7.3	3.4 (0.7–16.0)	0.118	6.6	3.1 (0.6–14.5)	0.159
School 3	130	12.3	1.2 (0.5–2.9)	0.630	7.7	1.1 (0.4–3.3)	0.791	4.6	2.1 (0.4–10.6)	0.369	9.2	2.8 (0.6–13.7)	0.192
Defecation practice
Sanitary latrine	109	8.3	ref.		4.6	ref.		1.8	Ref.		4.6	ref.
Open air	114	20.2	2.8 (1.2–6.4)	0.014	13.2	3.2 (1.1–8.9)	0.032	9.6	5.7 (1.2–26.4)	0.026	7.0	1.6 (0.5–4.9)	0.442
Both	212	18.4	2.5 (1.2–5.4)	0.019	9.9	2.3 (0.8–6.2)	0.106	9.0	5.3 (1.2–23.0)	0.027	4.7	1.0 (0.3–3.1)	0.958
Hand washing habit
Always	126	4.8	ref.		4.8	ref.		1.6	ref.		1.6	ref.
Never	86	22.1	5.7 (2.2–14.9)	0.000	8.1	1.8 (1.0–5.5)	0.049	10.5	7.2 (1.4–34.4)	0.013	14.0	10.1 (2.2–46.1)	0.001
Sometimes	223	20.6	5.2 (2.0–12.6)	0.000	12.6	2.9 (1.2–7.1)	0.023	9.4	6.4 (1.5–27.9)	0.013	4.0	2.6 (1.6–12.3)	0.003
Flood at home
No	291	12.7	ref.		7.1	ref.		4.8	ref.		3.4	ref.
Yes	144	23.6	2.2 (1.3–2.6)	0.004	13.9	2.1 (1.1–3.9)	0.027	12.5	2.8 (1.4–5.9)	0.005	9.0	2.8 (1.2–6.5)	0.018
Type of floor
Pucca‡	125	18.4	ref.		9.4	ref.		8.0	ref.		6.4	ref.
Kaccha	310	15.5	0.8 (0.5–1.4)	0.457	9.6	1.0 0.5–2.0)	0.937	7.1	0.9 (0.4–1.9)	0.744	4.8	0.7 (0.3–1.8)	0.512
Handwashing station at school
No	280	18.6	ref.		10.7	ref.		8.6	ref.		7.1	ref.
Yes	155	12.3	0.6 (0.3–1.1)	0.090	7.1	0.6 (0.3–1.3)	0.219	5.2	0.6 (0.2–1.3)	0.197	1.9	0.2 (0.07–0.9)	0.030
Deworming in the last year
Yes	277	15.9	ref.		8.3	ref.		6.5	ref.		5.8	ref.
No§	93	18.3	1.2 (0.6–2.2)	0.590	11.8	1.5 (0.3–3.2)	0.311	10.8	1.7 (0.8–3.9)	0.184	6.5	1.1 (0.4–2.9)	0.812
Doubtful§	65	15.4	0.9 (0.5–2.0)	0.921	10.8	1.3 (0.5–3.3)	0.528	6.2	0.9 (0.3–2.9)	0.919	1.5	0.3 (0.03–1.9)	0.189

CI = confidence interval; OR = odds ratio; sig. = p-value; STH = soil-transmitted helminth; % inf = percentage of children infected, denominator being the number of children enrolled in that category (N).

^*For age category, the lower limit is the completed given age (in years) and the higher limit is completed given age (in years) up to 1 day less than the succeeding year.

^†Refers to number of children positive for at least one species of soil-transmitted helminth.

^‡The variable Pucca indicates concrete flooring of the whole house, and the variable Kaccha indicates complete or partial earthen flooring.

^§Recategorizing the response “doubtful” as “No”, we observed a sig. (P value) of 0.744, 0.291, 0.366, and 0.547, respectively, for “any STH”, Ascaris, hookworm, and Trichuris in univariable logistic regression analysis. OR and corresponding 95% CI for each of the four outcomes are 1.1 (0.6–1.8), 1.4 (0.7–2.7), 1.4 (0.7–2.9), and 0.8 (0.3–1.9), respectively.

We discovered that the households of around one-third of the children (33.1%) were affected by flood at least once in the last year. Most households (71.3%) had a complete or partial earthen floor. If all the rooms of the living area had an earthen floor, it was regarded as complete; and if any of the rooms or veranda/front yard had no earthened floor, it was regarded as partial. Of the four schools, only one had a handwashing station (water supply from a tap/tubewell) with availability of soap, and two schools did not have any. The fourth school had two campuses; although the one for senior classes had a washing station, the other campus for primary classes did not have it.

As per the principals’ report, all the schools were provided deworming treatment with a single oral dose of 400 mg Albendazole. However, 63.7% reported having taken anti-helminthic medicine at least once in the last year. It was noted that 21.4% had not taken any deworming treatment, which could be because of the absence of the child from the school or the stigma associated with taking medicines. The remaining (14.7%) students either left the questionnaire blank for that question or were not sure.

Analysis of factors associated with STH infection.

The potential associated factors were explored for their probable link with STH infection by using univariable and multivariable logistic regression. The Chi-square test indicated a probable association with age group, place of residence, defecation practice, handwashing habit, and flood-affected dwelling place (Supplemental Table 2). Table 3 and Table 4 enumerate the results of univariable and multivariable analyses of risk factors for the acquisition of STH infections.

Table 4.

Multivariable analysis (binomial logistic regression model) of factors associated with STH infections

	Any STH		Ascariasis		Hookworm		Trichuriasis
Characteristics	Adj. OR (95%CI)	sig.	Adj. OR (95% CI)	sig.	Adj. OR (95% CI)	sig.	Adj. OR (95% CI)	sig.
Age category
5–7 years	ref.		ref.		ref.		ref.
8–10 years	1.9 (1.0–3.5)	0.050	1.9 (0.9–4.2)	0.113	1.3 (0.5–3.2)	0.607	–	–
11–13 years	1.0 (0.4–2.4)	0.967	1.1 (0.4–3.4)	0.839	1.3 (0.4–4.5)	0.674	–	–
Place of residence
School 4	ref.		ref.		ref.		ref.
School 1	2.4 (0.6–8.7)	0.182	1.6 (0.3–7.8)	0.245	10.0 (1.5–77.6)	0.028	0.2 (0.02–2.3)	0.193
School 2	1.6 (0.6–4.6)	0.355	1.2 (0.3–4.4)	0.573	3.3 (0.6–19.6)	0.183	0.6 (0.1–4.8)	0.611
School 3	1.2 (0.3–4.5)	0.797	1.0 (0.2–5.3)	0.996	2.9 (0.3–26.3)	0.340	0.3 (0.03–3.5)	0.351
Defecation site
Sanitary latrine	ref.		ref.		Ref.		–	–
Open air	2.8 (1.2–6.6)	0.020	2.9 (1.1–8.6)	0.049	5.9 (1.2–28.7)	0.028	–	–
Both	2.6 (1.2–5.9)	0.019	2.3 (0.8–6.4)	0.124	6.1 (1.3–28.2)	0.021	–	–
Hand washing habit
Always	ref.		ref.		ref.		ref.
Never	5.7 (2.1–15.3)	0.000	1.7 (0.8–5.3)	0.070	6.3 (1.3–31.3)	0.024	9.1 (2.0–42.2)	0.004
Sometimes	5.2 (2.1–12.9)	0.001	2.8 (1.1–7.1)	0.030	6.7 (1.5–28.2)	0.013	2.6 (0.5–11.5)	0.272
Flood at home
No	ref.		ref.		ref.		ref.
Yes	1.9 (1.1–3.4)	0.019	1.9 (1.0–3.7)	0.054	2.7 (1.2–6.1)	0.013	2.8 (1.2–6.7)	0.013
Hand washing station at school
Yes	ref.		ref.				ref.
No	0.9 (0.4–2.5)	0.705	0.8 (0.2–2.8)	0.743	1.6 (0.4–6.5)	0.476	0.2 (0.02–0.9)	0.033
Deworming in the last year
Yes	–	–	–	–	ref. ref.		ref.
No	–	–	–	–		0.170	–
Not sure	–	–	–	–	–	0.738	–

Adj. OR = adjusted odds ratio; CI = confidence interval; sig. = P-value; STH = soil-transmitted helminth.

The age group of 8–10 years was found to be more significantly associated with any STH infection (P = 0.015) when compared with pupils less than 8 years of age. Ascaris lumbricoides infection was also found to be significantly high in this age category [OR = 2.5, 95% CI = 1.0–4.5, P = 0.050]. Children attending School 1 had 9.4 times higher risk of hookworm infection and 3.5 times greater risk of overall STH infection (P = 0.004) (Table 3). No significant difference for male or female gender was found. Also, there was no religion-based difference in the risk of any STH infection.

Behavioral factors, such as defecation practices and handwashing habits, were discerned to be strongly associated with overall STH prevalence as well as individual geohelminth species prevalence. Children practicing outdoor defecation either routinely or occasionally had a high risk of STH infections [always open-air: OR = 2.8, 95% CI = 1.2–6.4, P = 0.014; both open-air and toilet: OR = 2.5, 95% CI = 1.2–5.4, P = 0.019]. Maximum risk was seen for hookworm (5.7 times higher in case of exclusive open defecation and 5.3 times higher in practicing both), followed by Ascaris lumbricoides (open: 3.2 times higher; both: 2.3 times higher). However, no association was found in case of Trichuris trichiura. The absence of the habit of washing hands with soap and water after defecation (practicing other methods such as only water or rubbing hands with soil or using soap occasionally) was strongly associated (P < 0.001) with all STH infections, and such children were at high risk [never use soap: OR = 5.7, 95% CI = 2.2–14.9; sometimes use soap: OR = 5.2, 95% CI = 2.0–12.6].

Children whose dwelling places were ravaged by flood at least once during the last year were at increased odds of all STH infections [OR = 2.2, 95% CI = 1.3–2.6, P = 0.004], particularly hookworm [OR = 2.8, 95% CI = 1.4–5.9, P = 0.005]. Having a handwashing station at school was observed to be protective against Trichuris infection when compared with not having the facility [OR = 0.25, 95% CI = 0.07–0.9, P = 0.030]. However, no significant association of STH infection with preventive deworming in the last (one) year was seen.

After adjustment in the multivariable model (Table 4), the factors of the age group of 8–10 years, the practice of open defecation and both toilet/open, the habit of never or occasional use of soap for handwashing after defecation, and dwelling places affected by flood remained significantly associated with any STH infection. The place of residence of Rangapani was independently associated with hookworm infection, and the presence of a handwashing station at school was found to be protective against Trichuris after adjusting for other variables in the multivariable model.

DISCUSSION

WHO Strategic Plan 2011–2020 had set specific targets for parasitological monitoring, such as “100% of countries requiring preventive chemotherapy for STH has to regularly assess intensity of infections in sentinel sites [by 2020]”⁶ However, there was a paucity of data on the prevalence and intensity of STH from the flood-ravaged Lower Assam. The prevalence rates for any STH, Ascaris, hookworm, and Trichuris identified in this study were much lower when compared with ecologically similar neighboring areas of Upper Assam.^10–12 Nonetheless, all these studies in the neighboring areas of upper Assam were conducted prior to 2010. Studies from Uttar Pradesh, Bihar, and South India (Visakhapatnam) also reported a high STH prevalence of 75.6%, 68%, and 91% respectively (studies conducted in 2015, 2011, and 1997–98, respectively).^17,19 However, our findings are consistent with the studies conducted in the neighboring states of North Bengal (2016) and Orissa (2015).^20,21 Sharma et al. documented a low prevalence of Ascaris lumbricoides (10.6%), Trichuris trichiura (6.2%), and hookworm infestations (3.9%) in the four districts of Bongaigaon, Barpeta, Kamrup, and Dibrugarh in Assam.²² Another study from South India also reported a low prevalence of STH.²³ Thus, a changing pattern could be noticed in the epidemiology of STH over the last 20 years in Assam and the adjoining states, which is probably a result of the mass deworming strategy prevalent in India in the past two decades. In their, study, Bah et al. found a considerable decrease in any STH prevalence from 48.3% in 2008 to 18.3% in 2016 in Sierra Leone.²⁴

Our study further uncovered that demographic and behavioral factors and conditions prevailing at home and school were associated with STH infections. Increasing age is known to be a protective factor for Ascaris and Trichuris,^18,24–26 and a risk factor for hookworms.²⁷ But our study observed higher odds of having any STH, particularly roundworm, in the age group of 8–10 years compared with younger ages. This is in concordance with similar findings by Gabrie et al. and Abossie et al.^28,29 Nevertheless, validity of this observation should be assessed with larger sample size and/or longitudinal studies in this region. Children belonging to the Rangapani (School 1) area were found to have 3.5 times higher odds of being infected with any STH, and a strong association with hookworms (P = 0.004) was observed in the multivariable model. The low socio-economic conditions of the people living in this area and their dependence on fishing and farming for earning a livelihood may be the reasons for the high prevalence. Although it is a widely known fact that hookworm infections are more common in males, this study found that a higher percentage of girls were infected by hookworm (7.6% versus 7.1%; OR = 1.1; Table 3). However, female preponderance was not found to be statistically significant in univariable analysis.

The most striking finding of this study was the strength of the association between the prevailing unhygienic behavioral practices and the prevalence of all three geohelminths. Sub-factors such as occasional use of sanitary latrines or practicing handwashing with soap and water “sometimes” after defecation were explored and proven to not have any protective role when compared with not using them at all. These unhygienic practices of under-use and indifference to hygienic handwash are deeply entrenched in the cultural norms and practices of rural India.^9,30,31 Approximately 520 million people in India (almost 40% of the total population) still practice open defecation.³² Under the Swachh Bharat Mission (Phase I) launched in 2014, the Government of India has constructed over 100 million household toilets across the country.³³ However, a major chunk of the population, particularly children, still indulges in the generations-old habit of open defecation, despite having access to toilets, as was observed in this study (48.7% of the children reported irregularities in toilet usage versus 25% of the children using sanitary toilets). Thus, behavioral change and awareness of hygienic practices, such as proper handwashing and personal cleanliness, among the masses are crucial for decreasing the prevalence of STH infections. Behavior-change curricula, such as community-led total sanitation (CLTS), have been implemented throughout the nation, but there is inconclusive evidence regarding the effectiveness of CLTS in encouraging the regular use of toilets.³⁴

Assam lies in the heart of monsoon belt and hence gets overburdened with heavy rainfall and floods every rainy season. Risk of infections (commonly water-borne diseases, gastroenteritis, cutaneous infections, etc.) after exposure to flood water captures considerable public health attention in Assam. However, an association with the increased risk of STH infections has not been documented. This study observed a strong association of children living in flood-affected homes with all soil-transmitted helminthiasis. This link may be because of the flood water contaminating drinking water sources, vegetable fields, etc., coupled with severe and almost inevitable breach of hygienic practices in the post-flood scenario. Collectively, we were unable to find a plausible explanation for this finding in the literature; thus, further explorations are warranted. Our study also determined that presence of a proper handwashing station with soap in the school was significantly associated with an 80% reduction in the odds of having Trichuris infection but not the other two worms. This finding is important in formulating a strategy for the mandatory requirement of having a proper handwashing station in every school.

From 2015, mass drug administration is being conducted across 27 districts of Assam as a fixed-day strategy.¹⁴ Accordingly, all students from the four included schools were receiving Albendazole (400 mg) as a once-daily dose biannually on the 10th day of February and August. MDA was last administered in the month of February 2017 in the four selected schools. Our study recorded marginal protection in children receiving PC (15.9% infected among the dewormed children versus 18.3% among the children not receiving PC); however, no statistically significant association was observed in univariable analysis. Similar observations were noticed in individual infections by the three species of helminth parasites found in the study area (Table 3). Recategorizing the response “doubtful” as “No”; and exploring further, no significant correlation was observed between non-adherence to PC and STH infection (see the footnote of Table 3). Our result is in concordance with a study by Torres et al.³⁵ Although it is a fact that PC is instrumental in bringing down the prevalence and intensity of soil-transmitted helminthiasis,^23–25,28 this result is worrisome and contrary to what is expected, considering the six-monthly deworming campaigns. However, several host-specific factors such as behavior, personal hygiene, and occupation and environmental factors such as sanitation facility, household clustering, and climate play an important role in early transmission, thereby resulting in reinfection.²⁵ The rate of reinfection is specific to certain species of helminths and depends on the life expectancy of that species (short-lived helminths reinfect more rapidly), the intensity of transmission within a given community, and the treatment efficacy and coverage.²⁵ Several studies have reported reinfection after preventive deworming.^11,35–39 STH re-infections occur rapidly after treatment, particularly for A. lumbricoides and T. trichiura.³⁶ Furthermore, deworming days can be adjusted in the monsoon season to fall on days during which the climatic conditions in the area are favorable for the transmission of the geohelminths. Efficacy of and resistance to the anti-helminthic drugs is another aspect that needs to be explored further.⁴⁰ We learned an important lesson—that the control of STH does not stop with the sustained distribution of medicines. Water, sanitation, and hygiene (WaSH) behaviors are important in curbing STH transmission; and therefore, WaSH strategy constitutes an important element of STH control alongside regular deworming.

One limitation of the study is that all the surveyed schools were government-run institutions. Private school students and out-of-school children were not included in the study. Because there is a considerable difference in the socio-economic conditions of children attending private and government-run schools, there may be slight variations in the actual estimate of STH prevalence. Another limitation is the low sensitivity of microscopy-based methods for detecting helminthic ova in stool, especially when the number of ova present in the stool sample are few.⁴¹ However, we tried to overcome this limitation by examining three consecutive day samples.

CONCLUSION

There is a considerable decrease in the prevalence of STH when compared with previous data from Assam. However, the unhygienic practices of the people still continue to be risk factors for STH infections. Thus, the findings of this study call for an integrated approach of various sectors, both governmental and nongovernmental organizations, to achieve STH control in Assam and lead to enhanced health outcomes. PC needs to be continued, and its frequency and timing need to be adjusted according to the prevalence and intensity of infection as well as the prevailing climatic conditions of the region. Besides, more effort should be given to create behavioral changes among the masses and make them more aware of personal hygiene. Flood control measures and environmental management especially during post-flood scenario may play a crucial role. Infrastructural upliftment of schools and homes to provide safe water, sanitary toilets, and flood control measures are a worthwhile benefit.

Note: Supplemental questionnaire and tables appear at www.ajtmh.org.