The effect of schistosomiasis and soil-transmitted helminths on expressive language skills among African preschool children - BMC Infectious Diseases - BMC Infectious Diseases
Design and setting of the study
Our study area was a small rural town of Ingwavuma, located in northern KwaZulu-Natal province of South Africa, close to the borders of eSwatini (in the north) and Mozambique (in the east). Ingwavuma is under traditional authority and is regarded as the worst poverty-stricken area in KwaZulu-Natal with an estimated annual income of R32 812 ([19] p. 17). Most people in this area depend heavily on social grants estimated to R13 090 per annum (less than $1000) as their main source of income [19]. The prevalence of Schistosoma haematobium among school aged children (over 10 years) in Ingwavuma is 37.5%. However, among the 1–5 years age group prevalence for both S. mansoni and S. haematobium is 2% [20]. The risk factors for schistosomiasis among young children include the caregiver's age, type of household head, poor sanitation, access to water source and knowledge about schistosomiasis [21].
The study was an analytical cohort study which described and compared language skills of non-infected and infected children with schistosomiasis and STH using clinical assessments and observations to obtain data. It was an ancillary study to the Tackling infections to benefit Africa (TIBA SA) project (http://tiba-partnership.org/about/what-is-tiba). Over 700 preschool children were tested for STH and schistosomiasis in the TIBA study between 2017 and 2020. Schistosoma haematobium was diagnosed using the filtration technique on urine samples [22]; S. mansoni and STH (Taenia, Ascaris Lumbricoides, Trichuris Trichiura) were diagnosed from stool samples using the Kato Katz technique [23].
Purposeful random sampling was used. To be eligible for the study a child had to be of age between 4.0 and 6.11 years; attend an isiZulu medium preschool or ECD in the target area, have no developmental delays, be monolingual isiZulu speaker and pass a hearing screening test. The study participants were striated based on age (4–6 years), gender (50% of each gender) and inclusion of infection positive participants at a ratio of 2 negative cases for every 1 positive case. The principal researcher was blinded to both status and nature of infection of the study participants. Children were tested in two phases; phase 1 was testing immediately after parasitology screening and phase 2 was testing at least 12 weeks later and after treatment of children with schistosomiasis and STH with oral Praziquantel. Some children participated in both phases while some participated only in phase1 and could not be traced for repeat testing. The data for the children who participated in both phases was treated separately because the phases were 3 months apart (affecting the children's level of maturity) and the language test was adapted for phase 2 to reduce content bias.
Sample characteristics
The distribution of children in phase 1 and 2 varied in terms of age, gender and infectious agents as shown in Table 1. The mean age was 4 years 9 months in phase 1 and 5 years 9 months in phase 2. The total number of children positive for schistosomiasis (23%) was less than the number of children positive for STH (33%) with the infectious agents not necessarily co-existing. The spectrum of infections in phases 1 and 2 indicated that STH infection resulted mainly from A. Lumbricoides (16%).
Seventeen preschools participated in the study; all had pit latrine toilets, one had a rainwater harvest tank within the facility and all of them provided one free meal a day for the children. During our test dates, we observed that the school meals did not include meat and vegetables other than beans. All preschool teachers involved possessed the minimum ECD qualification of high school education and a teaching diploma for Grade R. All 17 preschools had government supplied grade R books, but none had a computer, a television or internet access and generally they all did not have adequate educational resources such as puzzles and board games.
Data collection procedures
Considering the socio-economic profile of the study area, children were provided with a peanut butter sandwich and orange juice before undergoing testing to ensure they had a healthy breakfast and had energy to participate in the tests. Testing started with hearing screening which, included otoscopic examination and tympanometry to exclude ear infections and its contribution to poor language scores [18]. A nutritionist calculated the body mass index-for-age (weight in kg) and height-for-age (height and arm circumference in cm) to determine stunting classified as mild (1), moderate (2) or severe (3) [24]. The prevalence of stunting was 26%, showing that the majority of participants had adequate nutrition and, no correlation was found between the test scores and stunting in both phases of the study.
All children were monolingual, speaking isiZulu at home and at school. The Developmental Language Test [25], a non-standardised test developed for a research project, was adapted for this study following a pilot study and observations by research assistants. From these observations the test's vocabulary was adjusted to include local dialect (Northern KwaZulu-Natal coast) and the sequence of test items was formatted into 5 sections for easy scoring and interpretation as shown in Table 2. New test illustrations were developed using pictures taken in Ingwavuma with local community members for improved clarity and to accommodate the adjusted format of the test (see Additional file 1: Appendix A for test illustrations and B for test form).
The adapted Developmental Language Test showed a sensitivity of 89.7% in phase 1 and 81.3% in phase 2 reflecting that children who tested positively were true positives while specificity was 10.3 and 18.8%, respectively. The Cronbach's Alpha was determined to be 0.869 (SD = 5.1) in phase 1 and 0.813 (SD = 7.7) in phase 2 demonstrating adequate internal consistency and suggesting that all items measured the same construct.
The test was administered to one child at a time by the principal researcher who is a speech- language therapist and an isiZulu speaker, familiar with dialect and culture of the area. Scoring points varied from 0 to 4 points per target, depending on the extent of the answer as described in the test form (Additional file 1: Appendix B). Scoring was immediate and automated via the kobo collect app, an open source platform used for collecting and analysing data [26].
Data analysis
Quantitative data analysis for both phases comprised of descriptive frequency analysis, Independent paired samples t-tests, ANOVA and Bivariate correlations on the SPSS (Statistical package for Social Scientists, v. 25, IBM, Chicago, IL, USA). Post hoc tests were conducted using Bonferroni corrections to measure the specific contribution of variables such as age, gender, school and infection on language categories and time taken to complete the test. The overall error rate was controlled by the use of adjusted significance levels (α = 0.05). Information processing model for cognitive skills [27] and Vygotsky's sociocultural theory for development and learning guided data analysis and interpretation of scores [28].
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