Decreased Weight-for-Age Associated with Mass Deworming among Young Ethiopian Schoolchildren in Jimma Town, Southwest Ethiopia: A School-Based Cross-Sectional Study

ABSTRACT.

School-based mass deworming programs are implemented to reduce soil-transmitted helminth (STH) infection prevalence and intensity among school-aged children. However, previous studies debate the impact of deworming beyond the removal of worms. Hence, this study aimed to examine the effect of mass deworming on nutritional indicators in young Ethiopian schoolchildren. A school-based cross-sectional study was conducted among 1,036 participants from April to May 2020 in Jimma Town, Ethiopia. An interviewer-based questionnaire was administered to the children to gather data on sociodemographic, lifestyle variables, and deworming status. Anthropometric measurements were taken for the height and weight of the children. Stool samples were collected and analyzed for STH infection using direct wet mount microscopy and the Kato-Katz technique. In multivariate logistic regression analysis, deworming within the past 6 months or 1 year was not significantly associated with underweight, stunting, and thinning. However, deworming within the past year was significantly associated with decreased weight-for-age z-score (adjusted mean difference = −0.245; 95% CI: −0.413 to −0.076; P = 0.004). Deworming in the past 6 months demonstrated a nonsignificant trend toward increased stunting (adjusted odds ratio = 1.258; 95% CI: 0.923–1.714; P = 0.145). This study provides evidence that deworming in the past 6 months or 1 year was not significantly associated with underweight, stunting, and thinning. However, deworming within the past year was associated with a significantly decreased weight-for-age z-score in young Ethiopian schoolchildren of Jimma Town after adjustment for confounding variables.

INTRODUCTION

Soil-transmitted helminth (STH) parasites have been identified by the WHO as a major source of intestinal infection, affecting more than 24% of the world’s population.^1,2 Soil-transmitted helminth infection is endemic in many countries throughout Central and South America, Southeast Asia, and Africa,³ and it is most prevalent in impoverished areas with poor hygiene.¹ These parasites are transmitted through the fecal-oral route. Soil-transmitted helminth eggs are expelled from the human host through feces, after which they can enter the soil for maturation; then, infected soil may be ingested through contaminated drinking water, unwashed vegetables, or children playing in the soil and putting their hands in their mouths.¹ In addition, hookworm eggs hatch in the soil, releasing larvae that mature into a form that can actively penetrate the skin. People become infected with hookworm primarily by walking barefoot on contaminated soil.

In 2010, the burden of STH infection worldwide contributed to 5.18 million disability-adjusted life years and 4.98 million years lived with disability.⁴ The intensity and morbidity of STH infection are highly related. Light infections are characterized by less severe symptoms, whereas heavy infections lead to intestinal manifestations, malnutrition, weakness, and impaired growth.¹ Several studies^5–16 have linked intestinal STH infection with development of nutritional disorders. These intestinal parasites often feed on host tissues, leading to diminished iron and protein levels; they may cause intestinal bleeding and anemia, and they can result in malnutrition through a variety of methods.¹

As part of an infection prevention strategy, the WHO recommends that all children of school age, regardless of infection status, be treated with deworming medicines, albendazole (400 mg) or mebendazole (500 mg), in regions of endemic STH infection owing to the efficacy and safety of these treatments.¹ Current practices include annual mass treatment in areas where worm infections are above 20% and multiple treatments annually with greater than 50% prevalence.¹⁷ Several studies documented that mass deworming using these drugs effectively reduced STH infection prevalence and intensity among school-aged children.^18–20 At the same time, others indicated the benefits of deworming beyond reducing the burden of STH infection, including improving health, nutrition, local economy, and school performance.^21–23 For instance, studies have found that deworming children with anthelmintic treatment was associated with weight gain,^24–26 reductions in wasting malnutrition, anemia,²⁷ improved cognitive outcomes,²⁸ and enhanced school performance.²⁹ However, there is a lack of agreement about reported deworming benefits in the literature. Comprehensive systematic reviews and meta-analyses of randomized trials by the Cochrane and Campbell collaborations^30,31 found no evidence of benefits on nutritional status, hemoglobin, cognition, school attendance, physical well-being, or survival. Despite the conflicting findings on deworming outcomes, children have continued enrolling in school-based deworming programs in most African countries. In Ethiopia, STH infections are distributed widely, with an estimated 96.7 million people living in STH-endemic areas; about 27.7 million of these are school-aged children.³² Strategies to prevent STH infections using a national deworming program have been launched by the Ethiopian Federal Ministry of Health to treat more than 80% of at-risk school-aged children in all endemic regions.³³ More than 19 million people have been treated with anti-helminthic drugs after the national deworming, with treatment coverage of 76.5–80.5%.^34,35 Although previous studies documented a reduction in STH infection prevalence and intensity after mass deworming in Ethiopia,^34–36 data still need to be provided on the effect of deworming beyond reducing the burden of STH infection. We therefore used our data to explore the impact of school-based deworming on nutritional indicators among children in the Jimma area of Ethiopia

MATERIALS AND METHODS

Study setting and design.

We conducted a school-based cross-sectional study in four randomly selected public elementary schools in Jimma Town, Ethiopia, from April to May 2020. Jimma Town is in the Oromia region, 352 km southwest of Addis Ababa, the capital city. The study area was previously described; briefly, the estimated population of Jimma Town is 210,000, and there are 14 public elementary schools in the town. Based on their geographical location from the center of the Town, the Jimma Town Office of Education grouped the schools into four groups, and one elementary school was selected randomly from each group to be included in this study (the study map was published previously).³⁷ The altitude of this region is 2,450 m above sea level, and average temperatures range from 15°C to 18°C. We selected the Oromia region for study because STHs are endemic within the population, so many schools participate in mass deworming programs to distribute deworming medications to students. In addition, this is an at-risk population because many households do not have access to clean drinking water, causing reduced sanitation in the area. Randomly selected students were instructed to gain consent from their parents or legal guardian after being given a thorough explanation of the study and its objective. After parents provided signed consent for the study, the schoolchildren were given the autonomy to decide for themselves whether they wished to participate.

Measurement and data collection.

We used an interviewer-based questionnaire to gather information about the participants’ socioeconomic and selected lifestyle variables. The questionnaire was translated from English to the local languages of Oromiffa and Amharic to increase the accuracy of the responses. We pretested the translated version of the questionnaire among nonparticipating parents for confirmation of the translation and feedback about the flow of questions. Responses to the questionnaire provided data about socioeconomic variables including age, sex, place of residence, household size, family occupation, maternal education, access to electricity and potable water, and family ownership of a latrine, radio, television, or phone. We also recorded information about the height and weight of the children as well as their deworming history. To address possible confounding variables, certain lifestyle variables were examined in the questionnaire, including commonly eaten foods, fruit washing, handwashing, open field defecation, and soil consumption. In study schools, one round of deworming drugs was administered (a single dose of mebendazole, 500 mg), and children did not receive any deworming prior to the parasitological survey. Stool samples were collected from the participants using leakproof containers and were processed immediately or within 30 minutes of sample collection. Specimens were examined using direct wet mount microscopy and the Kato-Katz technique at the Center for Molecular Biology and Neglected Tropical Diseases, Jimma University, Ethiopia.

Anthropometric measurements.

Height and weight of the participants were measured in duplicate, and the average of the two measurements was recorded. The children were measured without shoes and while wearing light clothes to increase the accuracy of the measurements. Participants were instructed to stand straight with their weight evenly distributed on both feet and with their arms resting freely at their sides. We used an easy glide bearing wall stadiometer for height measurements that had a reading precision of 1 mm. For weight measurements, we used a digital scale with children weighing under 50 kg having a reading precision of 50 g and children above 50 kg having a. reading precision of 100 g. Calibration weights were used in between measurements to maintain the accuracy of the scale.

Laboratory testing.

Direct wet mount microscopy.³⁸

About 2 mg of the fresh stool samples was combined with a solution of 0.85% NaCl using a wooden applicator stick until a uniform suspension of the stool was formed and placed under a 22 × 22-mm coverslip. Under a microscope at ×100 magnification, the sample was examined for evidence of parasitic infection. If infection was present, further analysis was conducted at ×400 magnification to identify the exact parasite species.

Kato-Katz technique.

After wet mount microscopy, all samples were also analyzed using the Kato-Katz technique on the same day of collection according to the WHO’s protocol.³⁹ With a nylon screen, a significant amount of the stool sample was pressed onto a flat surface. The surface of the screen was scraped using a spatula to filter the fecal sample. To maintain consistency in the amount of filtered fecal matter, we used a calibrated template of 41.7 mg. The fecal material was then transferred to a microscope slide and left to soak overnight in methylene blue glycerol solution, after which it was analyzed under the microscope for evidence of parasite eggs.

Exposure definition.

Deworming status was defined as receiving a single dose of mebendazole (500 mg) within the past 6 months or year before the survey. Children who did not receive mebendazole within this specified time frame, as determined during the questionnaire and confirmed by school records, were characterized as not dewormed.

Outcome definitions.

We examined specified binary outcomes of malnutrition including stunting, being underweight, and thinning using the WHO’s standard. z-Scores (SD scores) were used to report height-for-age, weight-for-age, and body mass index (BMI)-for-age. Children were classified as stunted and severely stunted based on a height-for-age z-score (HAZ) less than −2 and −3 SDs below the median of the reference population, respectively. Children were classified as being underweight and severely underweight based on a weight-for-age z-score (WAZ) less than −2 and −3 SDs below the median of the reference population, respectively. Children were classified as thinned and severely thinned based on a BMI-for-age z-score (BAZ) less than −2 and −3 SDs below the median of the reference population, respectively. In addition, we examined the continuous outcomes of mean differences in height, weight, HAZ, WAZ, and BAZ.

Statistical analysis.

Data were entered and coded in Microsoft Excel (Redmond, WA) and transported to WHO Anthro Plus software for conversion of height, weight, and age variables into HAZ, WAZ, and BAZ. All data were then transported to SPSS Statistical software version 24 (Chicago, IL) for analysis. To analyze the relationship between mass deworming and nutritional indicators in the school-based cross-sectional study, descriptive statistics were used to present sociodemographic variables and illustrate distribution of STH infection and binary outcomes of malnutrition. Prior to analysis of any association between deworming and malnutrition, univariate analyses were used to identify any potential confounding variables. Any variables potentially associated with either the exposure (deworming treatment) or the outcome (nutritional indicators) in the crude analysis, using a P value of < 0.30, were considered possible confounding variables. In addition, we included variables previously shown to be associated with nutritional indicators in the literature, including age, place of residence, household size, and maternal education.⁴⁰ Then, our hypothesis that deworming would be inversely associated with malnutrition, including stunting, underweight, and thinning, was assessed using stepwise multivariate logistic regression. We also analyzed the relationship between deworming and continuous outcomes of nutrition, including height, weight, HAZ, WAZ, and BAZ, through stepwise linear regression to assess the estimated mean differences of the associations as adjusted for confounding variables. Covariates were kept in the models if they were independently associated with the outcome at P < 0.30 or if association was demonstrated in previous literature. Probability values of < 0.05 were considered statistically significant for the main effects.

RESULTS

Characteristics of the study subjects.

Table 1 shows the distribution of sociodemographic characteristics among the study population. Of the 1,036 school-aged children included in the study, 51.9% were female. The mean age of the study population was 10.42 years (SD: 2.51 years). Most children lived in an urban setting (79.9%) with access to electricity in their house (95.1%) and potable water in their house (67.1%). Household size was four to seven people for most children (74.8%); 59.8% of children received deworming treatment in the past 6 months.

Table 1.

Distribution of sociodemographic characteristics

Variables	Frequency	Percentage
Sex
Male	498	48.1
Female	538	51.9
Age (years)
5–8	277	26.7
9–12	526	50.8
> 12	233	22.5
Place of residence
Urban	826	79.9
Suburb/rural	208	20.1
Household size
0–3	64	6.2
4–7	775	74.8
> 7	197	19.0
Maternal education
Illiterate	303	29.2
Primary school	427	41.2
High school	225	21.7
Higher education	52	5.0
Unknown	19	1.9
Family occupation
Merchant	191	18.4
Government employee	204	19.7
Skilled/daily labor	105	10.1
Farmer	75	7.2
Other	461	44.5
Electricity in house
Yes	981	95.1
No	51	4.9
Potable water in house
Yes	689	67.1
No	338	32.9
Family owns latrine
Yes	1,019	98.5
No	16	1.5
Latrine location
Inside	18	1.8
Outside	1,010	98.2
Family owns radio
Yes	575	55.7
No	547	44.3
Family owns television
Yes	819	79.3
No	214	20.7
Family owns phone
Yes	998	96.6
No	35	3.4
Open field defecation
Always	6	0.6
Sometimes	187	18.2
Never	829	80.6
Unknown	6	0.6
Washing hands after toilet
Always	511	49.7
Sometimes	490	47.6
Never	28	2.7
Washing fruits before eating
Always	33	3.2
Sometimes	691	67.9
Never	294	28.9
Consumption of soil
Always	5	0.5
Sometimes	50	4.9
Never	969	94.5
Unknown	1	0.1
Deworming in past year
Yes	641	61.9
No	395	38.1
Deworming in past 6 months
Yes	620	59.8
No	416	40.2
Food eaten most
Injera	812	78.4
Other bread/grain	48	4.6
All other foods	176	17.0

Table 2 shows the prevalence of intestinal parasite infection: 31.7% of the children were infected with at least one intestinal parasite, and 22.1% were infected with at least one STH. Of all STH infections, Ascaris lumbricoides was the most common (16.5%) followed by Trichuris trichiura (8.9%) and hookworm (0.5%).

Table 2.

Prevalence of intestinal parasite infection

Variables	Frequency	Percentage
Individual parasite infections
Ascaris lumbricoides	171	16.5
Trichuris trichiura	92	8.9
Schistosoma mansoni	114	11.0
Hookworm	5	0.5
Others	33	3.2
Any parasite infection
Yes	328	31.7
No	708	68.3
Any STH infection
Yes	229	22.1
No	807	77.9

STH = soil-transmitted helminth.

Prevalence of malnutrition.

Figure 1 and Supplemental Table 1 provide the distribution of malnutrition. The prevalence of stunting was 22.6%, and 4.6% of children were severely stunted. In addition, 48.9% of children were underweight, with only 0.9% severely underweight. The prevalence of thinning was 3.9%, with 0.6% of children severely thinned.

Figure 1.

Prevalence of malnutrition according to stunting, underweight, and thinning among schoolchildren from four public elementary schools in Jimma Town, Ethiopia. The prevalence of being underweight was highest at 48.9%, followed by stunting (22.6%) and thinning (3.9%). The prevalence of severe malnutrition was highest in stunting (4.6%), followed by underweight (0.9%) and thinning (0.6%).

Association of outcome and exposure variables with demographic variables.

A series of independent univariate analyses were conducted to examine the effect of sociodemographic variables on outcome and exposure variables (Supplemental Tables 2–6). There were no statistically significant differences between the outcome variables (stunting, underweight, and thinning) with most demographic and lifestyle variables, including place of residence, household size, potable water in the house, family owns latrine, latrine location, open field defecation, washing fruits before eating, soil consumption, family owns television, family owns phone, and food eaten most (Supplemental Tables 2–4). In addition, the exposure variables (deworming in the last 6 months and deworming in the last year) were not significantly associated with most demographic and lifestyle variables including household size, electricity in the house, potable water in the house, latrine location, open field defecation, washing fruits before eating, family owns radio, family owns television, and family owns phone (Supplemental Tables 5 and 6).

Association between deworming history and stunting, underweight, and thinning.

The prevalence of stunting was higher among children who had a history of deworming both within the past 6 months (14.3%) and within the past year (14.0%) than among those who were not dewormed within these time periods (8.3% and 8.6%, respectively). Deworming in the past 6 months demonstrated a nonsignificant trend toward increased stunting (adjusted odds ratio [AOR] = 1.258; 95% CI: 0.924–1.714; P = 0.145) (Table 3). Children who were dewormed in the past 6 months or past year were associated with increased odds of being underweight, though the difference did not reach statistical significance (AOR = 1.515; 95% CI: 0.824–2.785; P = 0.181 and AOR = 1.142; 95% CI: 0.616–2.117; P = 0.674, respectively) (Table 4). A similar pattern of non-significant association was observed between deworming and thinning (Table 5).

Table 3.

Multivariate logistic regression of stunting in relation to history of deworming treatment among schoolchildren in four public elementary schools in Jimma Town, Ethiopia

Variables	Stunting		COR (95% CI)	P value	AOR (95% CI)	P value
	Yes, n (%)	No, n (%)
Deworming in last 6 months
Yes	148 (14.3)	472 (45.6)	1.203 (0.891–1.625)	0.228	1.258 (0.924–1.714)*	0.145
No	86 (8.3)	330 (31.9)	1	–	1	–
Deworming in last year
Yes	145 (14.0)	496 (47.9)	1.005 (0.745–1.357)	0.973	0.962 (0.707–1.310)†	0.806
No	89 (8.6)	306 (29.5)	1	–	1	–

AOR = adjusted odds ratio; COR = crude odds ratio.

^*Adjusted for sex, age, family owns radio, family owns phone, and potable water in house.

^†Adjusted for sex, age, family owns radio, and potable water in house.

Table 4.

Multivariate logistic regression of being underweight in relation to history of deworming treatment among schoolchildren 10 years old and younger in four public elementary schools in Jimma Town, Ethiopia

Variables	Underweight		COR (95% CI)	P value	AOR (95% CI)	P value
	Yes, n (%)	No, n (%)
Deworming in last 6 months
Yes	35 (6.0)	18 (3.1)	1.300 (0.718–2.356)	0.387	1.515 (0.824–2.785)*	0.181
No	317 (54.5)	212 (36.4)	1	–	1	–
Deworming in last year
Yes	36 (6.2)	17 (2.9)	1.197 (0.654–2.188)	0.560	1.142 (0.616–2.117)*	0.674
No	338 (58.1)	191 (32.8)	1	–	1	–

AOR = adjusted odds ratio; COR = Crude Odds ratio.

^*Adjusted for sex and age.

Table 5.

Multivariate logistic regression of thinning in relation to history of deworming treatment among schoolchildren in four public elementary schools in Jimma Town, Ethiopia

Variables	Thinning		COR (95% CI)	P value	AOR (95% CI)	P value
	Yes, n (%)	No, n (%)
Deworming in last 6 months
Yes	24 (2.3)	596 (57.5)	1.007 (0.528–1.919)	0.984	1.020 (0.520–1.999)*	0.954
No	16 (1.5)	400 (38.6)	1	–	1	–
Deworming in last year
Yes	24 (2.3)	617 (59.6)	0.921 (0.483–1.757)	0.804	0.984 (0.502–1.928)*	0.962
No	16 (1.5)	379 (36.6)	1	–	1	–

AOR = adjusted odds ratio.

^*Adjusted for age, place of residence, household size, and maternal education.

Association between deworming history and continuous nutritional parameters.

Multivariate linear regression analyses were used to examine the relationship between continuous nutritional parameters and deworming status in the past 6 months. In the crude analysis, deworming in the past 6 months was associated with a borderline significant decrease in weight (crude mean difference [CMD] = −0.989; 95% CI: −2.147 to 0.169; P = 0.094); however, adjustment for sex, age, electricity in the house, family owns latrine, potable water in the house, latrine location, and soil consumption did not materially alter the findings. Deworming within the past 6 months was associated with trends toward decreased height (adjusted mean difference [AMD] = −0.227; 95% CI: −0.583 to 0.128; P = 0.210), and decreased HAZ (AMD = −0.084; 95% CI: −0.224 to 0.057; P = 0.242), though none of these associations reached statistical significance (Table 6). However, multivariate linear regression analyses demonstrated a statistically significant association between deworming in the past year and decreased WAZ (AMD = −0.245; 95% CI: −0.413 to −0.076; P = 0.004). In the crude analysis, there was a statistically significant association between deworming in the past year and decreased weight (CMD = −1.372; 95% CI: −2.539 to −0.205; P = 0.021), but the relationship was no longer significant after adjusting for age, sex, family owns latrine, latrine location, soil consumption, electricity in the house, and potable water in the house (AMD = −0.364; 95% CI: −1.097 to 0.368; P = 0.329) (Table 7).

Table 6.

Multivariate generalized linear model of nutritional parameters in association with deworming in the last 6 months among schoolchildren in four public elementary schools in Jimma Town, Ethiopia

Variables	n	Mean	SD	Crude mean difference (95% CI)	P value	Adjusted mean difference (95% CI)	P value
Weight (kg)
Dewormed	620	30.13	9.097	−0.989 (−2.147 to 0.169)	0.094	−0.342 (−1.075 to 0.391)*	0.360
Not dewormed	416	31.12	9.621	0 (reference)		0 (reference)
Height (m)
Dewormed	620	1.316	0.131	−0.236 (−0.587 to 0.115)	0.187	−0.227 (−0.583 to 0.128)†	0.210
Not dewormed	416	1.552	4.445	0 (reference)		0 (reference)
Height-for-age z-score
Dewormed	619	−1.293	1.050	−0.097 (−0.233 to 0.039)	0.163	−0.084 (−0.224 to 0.057)‡	0.242
Not dewormed	416	−1.196	1.159	0 (reference)		0 (reference)
Weight-for-age z-score
Dewormed	352	−0.674	1.005	−0.032 (−0.197 to 0.134)	0.706	−0.024 (−0.195 to 0.148)§	0.786
Not dewormed	230	−0.642	0.972	0 (reference)		0 (reference)
BMI-for-age z-score
Dewormed	619	−0.095	1.003	0.018 (−0.105 to 0.140)	0.774	0.016 (−0.106 to 0.139)‖	0.793
Not dewormed	416	−0.113	0.955	0 (reference)		0 (reference)

BMI = body mass index.

^*Adjusted for sex, age, electricity in house, family owns latrine, potable water in house, latrine location, and soil consumption

^†Adjusted for potable water in house, family owns television, and family owns radio.

^‡Adjusted for sex, age, potable water in house, latrine location, open field defecation, family owns radio, place of residence, washing fruits before eating, and soil consumption.

^§Adjusted for age, family owns latrine, latrine location, washing fruits before eating, soil consumption, and family owns phone.

^‖Adjusted for place of residence.

Table 7.

Multivariate generalized linear model of nutritional parameters in association with deworming in the last year among schoolchildren in four public elementary schools in Jimma Town, Ethiopia

Variables	n	Mean	SD	Crude mean difference (95% CI)	P value	Adjusted mean difference (95% CI)	P value
Weight (kg)
Dewormed	641	30.01	9.234	−1.372 (−2.539 to −0.205)	0.021	−0.364 (−1.097 to 0.368)*	0.329
Not dewormed	395	31.38	9.406	0 (reference)		0 (reference)
Height (m)
Dewormed	641	1.458	3.584	0.124 (−0.230 to 0.478)	0.491	0.121 (−0.234 to 0.477)†	0.503
Not dewormed	395	1.333	0.135	0 (reference)		0 (reference)
Height-for-age z-score
Dewormed	641	−1.284	1.079	−0.077 (−0.216 to 0.062)	0.275	−0.080 (−0.217 to 0.057)‡	0.252
Not dewormed	394	−1.206	1.122	0 (reference)		0 (reference)
Weight-for-age z-score
Dewormed	374	−0.740	0.988	−0.222 (−0.390 to −0.055)	0.009	−0.245 (−0.413 to −0.076)§	0.004
Not dewormed	208	−0.518	0.983	0 (reference)		0 (reference)
BMI-for-age z-score
Dewormed	641	−0.132	0.974	−0.078 (−0.201 to 0.046)	0.218	−0.065 (−0.189 to 0.059)‖	0.303
Not dewormed	394	−0.054	0.999	0 (reference)		0 (reference)

BMI = body mass index. Bold values indicate statistical significance.

^*Adjusted for age, sex, family owns latrine, latrine location, soil consumption, electricity in house, and potable water in house.

^†Adjusted for family owns radio.

^‡Adjusted for age, sex, soil consumption, potable water in house, and family owns radio.

^§Adjusted for age, soil consumption, latrine location, washing fruits before eating, and family owns phone.

^‖Adjusted for place of residence.

DISCUSSION

This cross-sectional study indicates that mass deworming within the past 6 months or 1 year was not significantly associated with underweight, stunting, and thinning. However, deworming within the past year was associated with a significantly decreased WAZ in young Ethiopian schoolchildren of Jimma Town after adjustment for confounding variables. We also found associations between deworming and decreased weight as well as being underweight, though these findings were not statistically significant.

The existing body of epidemiological evidence on the effects of mass deworming on childhood nutritional indicators has shown divergent results. Randomized controlled trials using albendazole administered every 6 months in children in India (6 months to 6 years of age),⁴¹ rural China (9–11 years of age), and Uganda (15 months to 5 years of age)⁴² and mebendazole (500 mg single dose) in Peru⁴³ showed no significant positive effect of deworming on various growth parameters. Others, however, contradict these trials in preschool-aged children, and found a positive impact of deworming on growth indicators.^26,27 Our finding is generally in agreement with the lack of significant effect of deworming on growth among Ethiopian schoolchildren. Interestingly, after adjusting for confounding variables, we found a significant association between deworming in the past year and decreased WAZ. This finding is not strange; a previous study from Zaire by Donnen et al.⁴⁴ documented significantly reduced weight gain after deworming children with mebendazole, and Awasthi et al.⁴⁵ found that there was a significantly smaller increase in the number of children stunted in the albendazole group compared to the placebo group. Although the exact reason why deworming negatively affects childhood growth is unknown, some speculate that benzimidazole carbamates could cause gastrointestinal upset and diarrhea. This argument was not supported by a cohort study,⁴⁶ which indicated that children treated with albendazole experienced fewer episodes of diarrhea than their control counterparts. An alternative explanation for the observed negative effect of the deworming intervention on childhood growth in this study could be the high rate of re-infection after treatments in most deworming settings,^47–49 where parasite-infected children may not have recovered from the previous illness, which still impacted nutritional outcome. Furthermore, this study was conducted in Ethiopia, where malnutrition is prevalent; factors other than deworming, such as socioeconomic status, food insecurity, and parent education, may contribute to childhood growth impairments.^50,51 Our findings are also consistent with prior studies reporting no significant effect on stunting, height, or HAZ score of children after deworming.^28,52–54 Stunting is a chronic indicator of health and may not show improvement after a short deworming program.

The findings of the present study should be interpreted with consideration of certain limitations. First, this was a cross-sectional study, which therefore limited our ability to draw causal relationships between deworming and nutritional indicators. Second, we used only a single stool sample collected at the start of the study to determine the infection status of the children, which may have led to underestimation of the prevalence of parasite infection within the population. To combat this, we used two separate laboratory testing techniques, direct wet mount microscopy and the Kato-Katz technique, to increase the sensitivity of parasite detection as recommended by the literature.⁵⁵ Third, although nutritional outcome was assessed objectively by directly measuring anthropometric indices of the study subjects during fieldwork, information about deworming uptake was based on interviewer-led questionnaire reporting and hence was susceptible to recall bias. However, we used a previously validated questionnaire implemented in deworming settings,⁵⁶ and our study population had a similar sociodemographic profile, suggesting that such bias is non-differential and unlikely to alter the study findings, although ruling out the possibility entirely is challenging.

Fourth, WASH (water, sanitation, and hygiene) interventions have commonly been associated with deworming and STH transmission.⁵⁷ We therefore added WASH-related variables (e.g., availability of potable water in the house, family latrine, latrine location, open field defecation habits, washing hands after toilet, and washing fruits) to a multivariate model to adjust the observed association for potential confounding effects. However, comprehensive WASH-related variables are difficult to capture using individual-level information, and a future study could benefit from collecting data at school, household, and community levels, where children spend most of their time.

In conclusion, our study provides further evidence of the lack of significant effect of deworming on childhood growth parameters. We also noted a significant decrease in WAZ scores in Ethiopian schoolchildren. This study supports the previous arguments that the benefits of deworming on childhood growth may be less than previously believed. However, the evidence needs to be more definitive, and a more controlled longitudinal study is required to confirm this study’s findings among Ethiopian schoolchildren.

Note: Supplemental material appears at www.ajtmh.org.