Prevalence and Risk Factors of Ascaris lumbricoides, Trichuris trichiura and Cryptosporidium Infections in Elementary School Children in Southwestern China: A School-Based Cross-Sectional Study

Background: Intestinal parasitic infections pose great public health challenges in school children in developing countries. The aim of this study was to assess the prevalence of A. lumbricoides, T. trichiura and Cryptosporidium among elementary school children in rural southwestern China. Methods: A school-based cross-sectional study involving 321 elementary school children was conducted in 2014 in the southwest of China. They were invited to provide a stool sample and interviewed about the sanitary situation and hygiene behavior. Stool specimens were examined for A. lumbricoides and T. trichiura using the Kato-Katz fecal thick-smear technique. The presence of Cryptosporidium was determined using a modified acid-fast staining method. Results: The prevalence of infection was 10.0% (95% CI: 6.9–13.8%) for A. lumbricoides, 25.2% (95% CI: 20.6–30.4%) for T. trichiura and 2.4% for (95% CI: 1.1–4.9%) Cryptosporidium. The prevalence of co-infection was 3.7% (95% CI: 1.9–6.4%) for A. lumbricoides/T. trichiura, 0.3% (95% CI: 0–1.7%) for A. lumbricoides/Cryptosporidium and 0.9% (95% CI: 0.2–2.7%) for T. trichiura/Cryptosporidium. Children from households using well or river water were associated with a greater odds of A. lumbricoides infection (aOR = 2.61, 95% CI: 1.12–6.05). Having a household lavatory was associated with a lower odds of T. trichiura infection (aOR = 0.50, 95% CI: 0.30–0.84). Children who had three meals at the school canteen on week days were at a lower risk of Cryptosporidium infection. The use of spring water as a water source was associated with lower odds of any intestinal infection (aOR = 0.56, 95% CI: 0.35–0.91). Conclusions: Our study calls for an intervention program of school-based deworming combined with health education, hygiene promotion and provision of safe water and improved sanitation.


Introduction
Infections with helminths (e.g., Ascaris lumbricoides, Trichuris trichiura and hookworm) and intestinal protozoa (e.g., Cryptosporidium and Giardia intestinalis) are global public health threats Fertilized eggs in the moist soil become infectious about two weeks later. Humans are infected through contaminated water and soil [16].
Preschool children and school age children; Hypoimmunity; Overcrowding; Poverty; Using stools to make fertilizer; Poor health education [16].
Worldwide, more than 1.5 billion people (24% of the world's population) are infected with STH, mainly including Ascariasis (819.0 million), huriasTricis (464.6 million), and hookworm infection (438.9 million). Nearly 70% of the global STH burden occur in Asia [4]. Results of China's second national survey for STH showed that the prevalence of A. lumbricoides and T. trichiura were 12.7% and 4.6%, respectively [19].

Trichuriasis
Adenophorea Trichuris trichiura Immature eggs in soil under favorable conditions take about three weeks to mature. Humans are infected through contaminated water and soil [16].
Cryptosporidium is transmitted via contaminated water or food, swimming or bathing in surface waters [6].
Animal contact; Children from 1 to 9 years old; Hypoimmunity Both high ambient temperature and high rainfall. Malnutrition Overcrowding [20].
Inadequate sanitation and safe drinking water coverage will increase the transmission of Cryptosporidium [20].
Cryptosporidiosis is an important cause of diarrhea disease, more common in developing countries (5% to >10%) than in developed countries (<1-3%) [6]. In China, the proportion of diarrhea cases caused by Cryptosporidium varies between 1.4% to 10.4% and prevalence among the general population range from 0.79% to 6.59% [21].

Study Area
The survey was conducted from 23 October to 3 November 2014 in Lw Primary School (Figure 1), Lw town, Puge County of the Liangshan Prefecture, southwestern China. Lw town features a complex topography of mountains and valleys with an average elevation of 1800 m. The regional climate is subtropical monsoon, characterized by mild winters and warm and humid summers. The annual rainfall is 900 mm with the main rainy season from May to October and occasional rain throughout the rest of a year. The average temperature for the region is approximately 20 • C. The local population is approximately 3000, most of whom are of the Yi ethnicity. The region is one of China's state-level poverty-stricken areas. Agriculture and animal husbandry are vital sources of household income. Unprotected contact with animals often causes local people to suffer from various zoonotic diseases.
At the time of the study, Liangshan Prefecture had poor sanitary conditions, especially at home, characterized by unsterilized drinking water and inadequate access to lavatories. At the time of the study, Liangshan Prefecture had poor sanitary conditions, especially at home, characterized by unsterilized drinking water and inadequate access to lavatories.

Participant Recruitment and Field Study Procedures
Schools are convenient sites for field surveys and school-age children are at high risk of helminths and protozoan infections. Lw Primary School of Lw town was selected with the help of the local health officials and all children from Grades 3, 4, 5 and 6 were selected for the survey. These four grades are selected because they are old enough have sufficient ability and good compliance to understand and complete the questionnaire. School teachers and the local health officials of the Center for Disease Control and Prevention (CDC) were invited to a sensitization meeting prior to our surveys. The study procedures and the structure of the questionnaire were explained in detail under the guidance of a unified protocol at the meeting. Health workers and teachers then informed all potential participants based on the protocol list and carefully explained the research objectives, procedures, and potential risks. A written informed consent form was obtained from the parents/guardians of the eligible students. A questionnaire and a clean plastic bag were distributed to the students by school teachers. Trained workers asked all participants carefully to ensure that each question was answered. Each participant was given a unique identification number.

Laboratory Procedures and Survey Measures
Stool samples were collected once for each participant and sent to the laboratory of the local CDC as soon as possible. For the diagnosis of helminth infection, three Kato-Katz thick smear slides were prepared within 24 h post-collection. Another two thin smears were prepared using modified

Participant Recruitment and Field Study Procedures
Schools are convenient sites for field surveys and school-age children are at high risk of helminths and protozoan infections. Lw Primary School of Lw town was selected with the help of the local health officials and all children from Grades 3, 4, 5 and 6 were selected for the survey. These four grades are selected because they are old enough have sufficient ability and good compliance to understand and complete the questionnaire. School teachers and the local health officials of the Center for Disease Control and Prevention (CDC) were invited to a sensitization meeting prior to our surveys. The study procedures and the structure of the questionnaire were explained in detail under the guidance of a unified protocol at the meeting. Health workers and teachers then informed all potential participants based on the protocol list and carefully explained the research objectives, procedures, and potential risks. A written informed consent form was obtained from the parents/guardians of the eligible students. A questionnaire and a clean plastic bag were distributed to the students by school teachers. Trained workers asked all participants carefully to ensure that each question was answered. Each participant was given a unique identification number.

Laboratory Procedures and Survey Measures
Stool samples were collected once for each participant and sent to the laboratory of the local CDC as soon as possible. For the diagnosis of helminth infection, three Kato-Katz thick smear slides were prepared within 24 h post-collection. Another two thin smears were prepared using modified acid-fast staining to detect the oocysts of Cryptosporidium. All the slides were read by two independent examiners and a third examiner was called in if there was a disagreement. The survey included information on demographic characteristics, risk factors, and sanitation conditions, which were associated with those three infectious diseases. Demographic characteristics data of school children included gender, ethnicity, age, and the number of family members. Risk factors of infections were based on four major items, including washing hands, eating raw food or drinking raw water, the place to eat, and engaging in farm work. Sanitation associated with the student's home were assessed by two items, including water sources and types of lavatories.

Ethical Considerations
This study was approved by the Ethics Review Committee of the Ethical Institute of the School of Public Health, Fudan University (reference No. #2010-08-0235). After the survey, all children with infection were offered free anti-helminthic treatment according to the national guidelines.

Statistical Analysis
Data were checked and entered into EpiData version 3.1 (EpiData Assoc., Odense, Denmark) and internal consistency checks were done. Statistical analyses were carried out with the SAS version 9.4 software (SAS Institute, Cary, NC, USA). Descriptive summary of the children's characteristics was computed as appropriate. Prevalence of A. lumbricoides and T. trichiura and Cryptosporidium infections with the 95% confidence interval were calculated. Fisher's exact test was used to compare the prevalence of the three parasitic diseases in different age groups. Univariate and multivariate analyses were performed to identify risk factors for the three parasitic diseases and any intestinal infection (any intestinal infection refers to the infection with one or more of those three infectious diseases). In the univariate analyses, Pearson's χ 2 test was used to examine the associations of participants' characteristics with A. lumbricoides and T. trichiura and Cryptosporidium infections by computing crude odds ratios (ORs) with 95% confidence intervals (CIs). A subsequent multivariate logistic regression model was employed to identify risk factors and adjusted ORs with 95% CIs were calculated. Since a correlation existed between living on campus and eating at the school canteen, have a household lavatory and types of lavatories at home, only one of the two related variables was included in the multivariate model at a time. A two-sided p-value of 0.05 or less was regarded as significant.

Results
There were a total of 348 eligible participants in the study. After exclusion of participants who did not provide feces or complete the questionnaires, 321 (92.2%) participants were included in the analysis. Demographic data showed similar distributions for those included and not included in the analysis ( Table 2). a Data are number (%) of participants unless otherwise indicated, and using chi-square test. b Data are mean ± SD, and using 2-independent-samples t-test. Table 3 shows the prevalence of A. lumbricoides, T. trichiura, Cryptosporidium and coinfections by age group. The prevalence of infection was 10.0% (95% CI: 6.9-13.8%) for A. lumbricoides, 25.2% (95% CI: 20.6-30.4%) for T. trichiura and 2.4% (95% CI: 1.1-4.9%) for Cryptosporidium. The prevalence of co-infection was 3.7% (95% CI: 1.9-6.4%) for A. lumbricoides/T. trichiura, 0.3% (95% CI: 0-1.7%) for A. lumbricoides/Cryptosporidium and 0.9% (95% CI: 0.2-2.7%) for T. trichiura/Cryptosporidium. No triple infection was found in our study. The prevalence of A. lumbricoides infection differed among the age groups and was the lowest among children over 13 years of age (p = 0.04), while T. trichiura and Cryptosporidium infections and all the co-infections were not significantly different among the age groups (Table 3). The characteristics of the participants are described in Table 4. The mean age of participants was 12.6 years (SD: 2.0). Among 321 children recruited, 62.93% were male; 98.75% were Yi people; 89.10% lived on campus and had their three meals of week days at the school canteen. At homes of the 321 participants recruited, 85.98% of the drinking water came from mountain springs, 60% of household lavatories were simple, and 30% were triple compartment or biogas pools.   Tables 5 and 6 show the results of risk factors associated with A. lumbricoides, T. trichiura and Cryptosporidium infections. Children from households using well or river water were at a greater risk of A. lumbricoides infection (aOR = 2.67, 95% CI: 1.15-6.20). Having a household lavatory was negatively associated with T. trichiura infection (aOR = 0.50, 95% CI: 0.30-0.84). Children having their three meals at the school canteen were at a lower risk of Cryptosporidium infection (aOR = 0.06, 95% CI: 0.01-0.40). Similarly, living on campus was also a protective factor for Cryptosporidium infection (cOR = 0.11, 95% CI: 0.03-0.46). Using spring water as water source was a protective factor for any intestinal infection (aOR = 0.52, 95% CI: 0.28-0.99).

Discussion
This study reported the prevalence of A. lumbricoides, T. trichiura and Cryptosporidium infections in the elementary school children. The prevalence of Cryptosporidium infections in our study (2.40%) was comparable to the provincial estimate (2.96%) in Sichuan Province, China [15]. The prevalence of A. lumbricoides infection (10.0%), was similar to the national prevalence (12.7%) of the second national important parasitic disease survey from 2001 to 2004, but was lower than those of Guizhou Province (42.0%) and Sichuan Province (27.7%) [13]. Our study area is located in the southwestern of Sichuan Province, close to Yunnan and Guizhou Province (Figure 1). The reduced prevalence of A. lumbricoides infections may be related to the government's deworming treatment of A. lumbricoides in high-risk populations. A survey of school-age children in 2010 also showed a reduction in the prevalence of A. lumbricoides infection in rural southwestern China [18]. For T. trichiura infection, the prevalence in our study (25.2%) was higher than both second national survey (4.6% in China Mainland) and the survey of school-age children in southwestern China in 2010 (14.3% in Guizhou Province, and 2.2% in Sichuan Province) [13,18]. According to the WHO report, the prevalence of STH infection in China was estimated to be less than 20% [22]. The prevalence of T. trichiura infections in the study area remained high. The main reason may be the unsatisfactory efficacy of currently recommended drugs against T. trichiura infection, especially when they are not regularly taken [23]. Poor hygiene, especially at home, may be another reason for the high prevalence of T. trichiura infection. Most children in the school drank unboiled water (84.42%) and ate raw food without washing (86.60%). Water, food, soil and hands are easily contaminated by worm eggs in the case of inadequate sanitation facilities and feces management, unsafe water and poor hygiene practices [24]. Therefore, improving access to adequate water, sanitation and hygiene (WASH) at the household level and in school is essential to prevent infections of T. trichiura [25]. In addition, the climatic factors in Liangshan Prefecture are within the plausible limits of STH transmission [5]. As expected, the prevalence of A. lumbricoides infection varied by age. However, the age patterns of T. trichiura and Cryptosporidium infections showed little variation, which probably reflected a combination of behavioral and socioeconomic factors [26]. Indeed, older students had more opportunities to receive health education and knowledge about infection prevention. Interestingly, although most hygiene habits tended to improve with age in our study, older students were prone to eating raw food. This finding emphasized the importance of continuing and strengthening health education programs targeting school children to reduce the intensity of parasites and the attendant morbidity [12].
A recent meta-analysis of the effects of water, sanitation, and hygiene (WASH) on STH infections reported that access to piped water and proper water treatment was associated with lower risks of A. lumbricoides and T. trichiura infections [27]. Our study found that using river or well water was associated with an increased risk of A. lumbricoides infection. In the study area, the main sources of drinking water in the study area were mountain springs (far from human living areas, piped after extensive precipitation and filtration), followed by wells or rivers (both close to living areas and susceptible to fecal pollution). Moreover, some students' homes (14.33%) used river or well water as the source of drinking water and 84.42% of school children were in the habit of drinking unboiled water. The drinking water is rarely disinfected and is often contaminated by untreated infectious human excreta, which puts the local residents at great risk of intestinal parasitic infections. Safer drinking water is an urgent need in the rural regions of Liangshan Prefecture. Having a household lavatory was negatively associated with T. trichiura infection, which was similar to previous findings [19,[27][28][29]. In order to reduce intestinal infectious diseases, the local government promoted and constructed triple compartment toilets or biogas digesters that can fully ferment feces to kill the eggs and ensure that human waste is safely separated from human contact in some rural areas [30,31]. But many families only have simple lavatories that pile up human stools and urine as a direct fertilizer. A cluster-randomized trial undertaken in Kenya demonstrated that school hygiene and sanitation reduced the re-infections of STH after school-based deworming [2]. A recent meta-analysis has shown that adequate sanitation is associated with the reduction of STH transmission risk (between 40% and 50% reduced infection rates) [28]. There is no doubt that improvements to water, sanitation, and hygiene (WASH) lead to a significant reduction in STH infection. Schools are available platforms, not only for health education but for sanitation improvements. School-age children are more likely to receive health education and tend to integrate new health behaviors into their daily lives [32].
Soil-transmitted helminthiasis, a group of NTDs, is thought to be associated with malnutrition and iron deficiency anemia, and has a negative impact on children's physical and cognitive development [33]. Hence, reducing risk factors and regular deworming become important strategies for controlling STH [34]. Effective control of STH can have a positive outcome on students' education, as chronic helminth infection impedes cognitive development and leads to growth delays, thus delaying enrollment and grade progression [35].
Cryptosporidium is typically transmitted by fecal-oral routes, through ingestion of human or domestic animal fecal-contaminated food or untreated water. In our study, students having meals at the school canteen or living on campus had lower odds of obtaining Cryptosporidium infection. Students who live on campus (89.10%) ate three meals at the school canteen. The elementary school we selected was basically a boarding school. The majority of the students stayed in the school dormitories for 5 days per week and returned home during holidays and weekends. One possible reason for the association of Cryptosporidium infection with eating in the school cafeteria was less chance of contact with domestic animals. Raising domestic animals is known as a risk factor for Cryptosporidium infection [36,37]. Another possible reason was that schools had better sanitation facilities and safer water, protecting those students who did not have access to these facilities at home [14,32,38]. The local government has been concerned about the safety of school drinking water. At Lw Primary School, improved water and sanitation facilities, including basic tap water, were available to the students. Tap water was used for handwashing without soap. A recent review showed that diarrhea and gastrointestinal diseases decreased as schools had access to adequate sanitation [39]. Improper waste disposal and unsafe water, especially at home, will increase the chance of transmission of fecal-oral diseases [14,40].
We recognize a number of limitations in our study. The diagnoses of three intestinal parasitic infections were based on a single stool sample and underestimation of the infection rates might be possible. There was also a lack of data on helminth infection intensities and Cryptosporidium genotypes. Further research is needed to determine the infection intensities of A. lumbricoides and T. trichiura and also the routes of transmission of Cryptosporidium among school children in this region. To truly understand the motivators for behavior and exposure to infection, further studies might be needed to systematically assess risk factors of intestinal parasites by using a combination of quantitative and qualitative methods including water quality monitoring and WASH spot checks [40]. The sample size is not enough for more accurate statistical analysis. In view of these limitations, the findings should be interpreted discreetly.

Conclusions
In summary, our study revealed a high burden of A. lumbricoides and T. trichiura infections among elementary school children in southwestern China. School-level interventions involving deworming, health education, improvement of environmental sanitation and hygiene and access to safe water might be required. Schools are a good platform for health education, not only for students but also for their families. New methods of health education (e.g., comic and animation) might be explored. There is no doubt that improving health awareness among students can reduce their risky behaviors related to parasitic infections. Similarly, we should actively promote the reconstruction of harmless lavatory (e.g., triple compartment or biogas) in rural areas and improve the rural sanitary conditions, to reduce the transmission of intestinal infectious diseases. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.