Impact of the health education and preventive equipment package (HEPEP) on prevention of Strongyloides stercoralis infection among rural communities in Northeast Thailand: a cluster randomized controlled trial

Study design

This study was an open-label controlled trial [Thai Clinical Trials Registry (TCTR), Medical Research Foundation of Thailand, Medical Research Network of the Consortium of Thai Medical Schools: MedResNet (Thailand) (identification number: TCTR20180404002)] that aimed to evaluate the impact of the Health Education and Preventive Equipment Package on prevention and control of S. stercoralis infection among communities in northeast Thailand from March 2016 to September 2017. Participants from one area served as an experimental group, while those from another area near the first served as the control group.

Study area and study population

This study was carried out in two areas of Kalasin province in northeast Thailand: (1) Nong Bua sub-district in Nong Kung Si district (intervention group) and (2) Phu Din sub-district in Mueang Kalasin district (control group). Both areas are located near Lam Pao dam. Nong Bua sub-district is located at 16.716733^° latitude and 103.383900^° longitude and Phu Din sub-district is located at 16.643328^° latitude and 103.517948^° longitude (Fig. 1). Residents of both areas are primarily agriculturists (i.e. working in rice fields, cassava, sugarcane, and Para rubber farms) [17]. The two areas were selected based on data from previous studies showing that the province had a high prevalence of strongyloidiasis [10, 18]. The sample size was determined using the command “clustersampsi, binomial sample size” in STATA Version 10.1 (College Station, Texas: StataCorp LLC). The STATA command that was used was “clustersampsi, binomial samplesize p1(.23) p2(.10) m(30) rho(0.034) alpha(0.05) beta(0.80)”. It was calculated based on the prevalence rate (p₁) of 23.0% found in a previous study [10], a prevalence rate after added intervention (p₂) of 10.0% with a 95% confidence interval (Z ²_∝/2 = 1.96), 80% confidence interval (Z_β = 0.84), design effect of 2, 10 clusters per arm, and an intra cluster correlation (ICC) of 0.034. The calculated sample size was 300 per area. We assumed that the final sample size would be reduced by around 20% due to unavailability of stool on the day of collection, making the adjusted sample size 360 per area. A simple random sampling method was used to select subjects from each sub-district. Subject inclusion criteria were that participants were 1) residents of Nong Bua or Phu Din sub-district and 2) age ≥ 20 years old. Subjects were excluded if they 1) had recently migrating from other areas or 2) dropped out of the study. Subsequently, they were given plastic containers for stool collection with instructions. In the end, a total of 689 subjects returned stool specimens, 349 from the six villages in the intervention group and 340 from the six villages in the control group (Fig. 2).

Baseline data collection and empirical methods

Baseline data collection included screening for eligibility and S. stercoralis infection diagnosis, as well as data from a questionnaire assessing participants’ knowledge and behavior with regard to S. stercoralis infection (see Additional file 1). The collection of data regarding demographic, socioeconomic, and environmental factors was conducted between January and May 2017. All participants who were infected with S. stercoralis underwent treatment and a subsequent follow-up 21–28 days post treatment (in June 2017). An intervention study was then initiated to evaluate the efficacy of the Health Education and Preventive Equipment Package (HEPEP) on September 2017 (Fig. 2).

Questionnaire

After giving written consent, research participants were interviewed in person at their homes using a three-part questionnaire which is developed for the present study. The first part consisted of demographic, socioeconomic, and environmental data; habits; and health status. The second part revolved around knowledge regarding S. stercoralis consisting of 15 questions. The questions in the second part were designed to test respondents’ knowledge regarding S. stercoralis (biology, transmission, symptoms, prevention, and control). The knowledge score was interpreted based on the method employed by Bloom et al. [19]: 13–15 (> 80.00%) = high level of knowledge, 10–12 (60.01–79.99%) = moderate level of knowledge, and 0–9 (0.00 to 60.00%) = low level of knowledge. According, the third part revolved around risk behaviors to S. stercoralis infection.

Stool examination

Stool samples were collected at baseline, follow-up (21–28 days post treatment), and 3 months later in both the control and intervention groups. Clean plastic containers labeled with the participants’ names and code numbers were distributed to all participants by VHVs in each village. On the following day, the full containers were returned to the field staff who performed agar plate culture (APC), as described by Koga et al. [20], for detection of S. stercoralis infection. Two to 3 grams of stool was added to 1% nutrient agar in a plate that was 9 cm in diameter. The agar plate was incubated at 25-27^๐C for 3–5 days in a dark box and was examined under a stereomicroscope on either the third or fifth day [20]. The plates were transported to the Parasitology laboratory at the Khon Kaen University Faculty of Medicine and observed under a stereomicroscope by qualified parasitologists. A negative result was recorded when S. stercoralis was not detected within 5 days of incubation.

Deworming

At baseline, follow-up, and three-months, participants who were infected with S. stercoralis were listed accordingly and received ivermectin (200 μg/Kg body weight, single dose; Atlantic Laboratories Corporation Ltd., Samut Prakan, Thailand). All participants were administered the medication under observation by a researcher and medical officer. There were no complaints from the participants during ivermectin administration.

Preventive equipment package and follow up

Health education was provided to participants in both groups, but the intervention group was provided with a preventive equipment package (gloves and boots) and detailed information regarding S. stercoralis in the form of a “Practices to Prevent Strongyloidiasis” poster (size 29 × 40 cm) to be hung in participants’ houses (see Additional file 2), vinyl boards containing information on S. stercoralis and strongyloidiasis (size 2 × 3 m) to be posted in each village (see Additional file 3), and a “S. stercoralis Life Cycle” poster (size 90 × 120 cm) (see Additional file 4) with a 20-min lecture explaining its contents. Subsequently, the intervention group was given a refresher course and their use of the equipment that was provided was checked every month by village health volunteers (VHVs). The control group was provided with only a five-minute lecture regarding human S. stercoralis infection. The participants from both areas were given follow-up S. stercoralis examinations and interviewed over the following 3 months (Fig. 2). The HEPEP-related follow-ups consisted of monthly visits to the villages in question by researchers and VHVs to observe the participants’ practices with regard to wearing shoes and gloves while working on their farms (see Additional file 5). In addition, the VHVs reminded the participants about S. stercoralis transmission monthly via a broadcast tower in each village (Fig. 2).

Statistical analysis

Frequency, percentage, mean, and standard deviation (SD) were used to describe demographic characteristics. Prevalence of S. stercoralis infection was described in terms of proportion and 95% confidence interval (95% CI). To investigate the impact of Health Education and Protective Equipment Package on S. stercoralis infection, the prevalence of S. stercoralis infection in the intervention group and that in the control group were compared using logistic regression and a generalized estimating equation (GEE). To investigate the impact of the Health Education and Protective Equipment Package on knowledge scores, knowledge scores at baseline and 3 months were compared using pair t-test. To investigate the impact of the Health Education and Protective Equipment Package on behavior in each group, behavior at baseline and 3 months were compared using a paired McNemar’s test. For adjusting possible confounders, all variables with a P-value less than 0.1 in the univariate analysis were selected. Additionally, the knowledge scores in the intervention and the control group were compared using a t-test. A P-value of less than 0.05 was considered statistically significant. The statistical analysis was conducted using the STATA package version 10.1 (College Station, Texas: StataCorp LLC).

Demographic characteristics

Two hundred seventy-eight of 689 the participants (40.35%) had adequate knowledge regarding S. stercoralis infection. The overall average knowledge score at baseline assessment was 71.69 ± (14.48; range = 0–100), with an average score of 73.81 (±11.11; range = 40–100) in the intervention group and 69.51 (±17.03; range = 0–93.33) in the control group (Table 1). In terms of participant behavior, 644 (93.46%) had direct contact with soil, 423 (65.68%) of whom had contact with soil in the area in which they farmed. Additionally, 540 participants (78.37%) used animal dung as fertilizer. One hundred fifty-five (22.50%) had used steroid drugs in the past. Importantly, 508 participants (73.73%) reported that they sometimes defecated into the surrounding environment, rather than using a latrine (Table 1). Differences in age, occupation, underlying diseases, presence of a pet in the house, area in which there was direct contact with soil, and use of animal dung fertilizers were statistically significant between participants in the intervention area and the control area (Table 1).

Prevalence of S. stercoralis infection at baseline

Two hundred twenty-six (32.80%; 95%CI: 29.29 to 36.32) of the participants were found to be positive for S. stercoralis infection according to APC (Fig. 3). The positive rate was higher in male (21.92%) than in female (10.88%) participants. The peak infection rate was found in 40–59 year-old participants (19.30%) (Fig. 3). The baseline prevalence of S. stercoralis infections in the intervention group and the control group were comparable 31.23% (95%CI: 26.40 to 36.38) and 34.41% (95%CI: 29.37 to 39.73), respectively with no statistically significant difference (Fig. 3). Twenty-eight days after treatment (follow-up), individual fecal samples of all participants were examined using APC. The prevalence of S. stercoralis infection had been reduced to 0% in both groups.

Impact of the health education and preventive equipment package on the prevalence of S. stercoralis at a three-month assessment

Three months after treatment, all participants were examined for the presence of S. stercoralis infection using APC. The prevalence of S. stercoralis infection in the intervention group and that in the control group were 2.75% (9/327) (95%CI: 1.27 to 5.16) and 6.60% (21/318) (95%CI: 4.13 to 9.92), respectively (Fig. 4). There was a statistically significant difference in the prevalence of S. stercoralis infection between the intervention group and control group. The efficacy of the HEPEP in the prevention of S. stercoralis infection was 60% according to univariable analysis (cOR 0.40; 95%CI: 0.18 to 0.89, P-value = 0.02) and 41% according to multivariable analysis (aOR 0.59; 95%CI: 0.41 to 0.85, P-value = 0.005; Fig. 4, Table 2).

Outcome variable	Unadjusted	Adjusted
	cOR (95% CI)	aORa (95% CI)
S. stercoralis prevalence	0.40 (0.18 to 0.89)**	0.59 (0.41 to 0.85)**

Remark: ^aOdds ratios adjusted for sex, age, education level, occupation, household income ($), underlying diseases, history of larva currens, presence of a pet in the house, direct contact with soil, use of animal fertilizer, and baseline S. stercoralis prevalence

**Statistically significant difference, P-value < 0.05

Impact of the health education and preventive equipment package on the knowledge of the participants in both groups

Impact of the health education and preventive equipment package on the behavior of participants at three months post-intervention