Complexities and Perplexities: A Critical Appraisal of the Evidence for Soil-Transmitted Helminth Infection-Related Morbidity
BACKGROUND Helminth (worm) infections are widespread and are thought to contribute to poor nutritional status, anaemia, and impaired growth and learning in children. OBJECTIVES To summarise the effects of anthelmintic drug treatment in children in relation to their growth and cognitive performance. SEARCH STRATEGY We searched the Cochrane Infectious Diseases Group trials register, the Cochrane Controlled Trials Register, Medline, Embase and the reference lists of articles. We also contacted experts in the field. SELECTION CRITERIA Randomised and quasi-randomised trials of drug treatment compared with placebo or no drug treatment for intestinal helminths in children. DATA COLLECTION AND ANALYSIS Trial quality was assessed and data were extracted independently by two reviewers. Study authors were contacted for additional information. MAIN RESULTS Thirty trials involving more than 1500 children were included. There was potential for bias from inadequate concealment of allocation. Studies varied in relation to target groups, drugs administered and treatment regimens. Compared to placebo or no drug treatment, drug treatment for helminths was associated with some positive effects on change in weight, height and skinfold thickness. However there was significant heterogeneity between the results of the trials. There were some positive effects on mean weight change in the trials reporting this outcome; after a single dose (any anthelminth) the pooled estimate was 0.24 kg, (95% CI 0.15 to 0.32; fixed effects model assumed); and 0.38 kg (95% CI 0.00 to 0.77; random effects model assumed). Results from trials giving multiple doses showed mean weight change under one year of follow up of 0.10 kg (95% CI 0.04 to 0.17; fixed effects assumed); or 0.15 (95% CI 0.00 to 0.30; random effects assumed). At more than one year of follow up, mean weight change was 0.12 kg (95% CI -0.02 to 0.26; fixed effects assumed) and 0.43 (95% CI -0.61 to 1.47; random effects model assumed). Results from studies of cognitive performance were mixed and inconclusive. REVIEWER'S CONCLUSIONS There is some limited evidence that routine treatment of children in areas where helminths are common has small effects on weight gain, but this is not consistent between trials. There is insufficient evidence to know whether this intervention improves cognitive performance. Our interpretation of these results is that the current public health programme investments in this intervention, based on the expectation that there will be an improvement in growth and learning, are not based on consistent or reliable evidence.