Methods to evaluate nutritional and economic implications of ascaris infection

Ascaris infection has important economic implications for human populations, due to its negative effects on growth of undernourished children and its less common role in causing intestinal obstruction. The deleterious effects of Ascaris infection on growth of undernourished children have been demonstrated in studies conducted in India, Kenya and Tanzania; deworming has resulted in improved weight gains of 20-35% compared with uninfected children. However other studies in Ethiopia, Bangladesh and Guatemala have not found statistically significant improvements in growth of children after treatment for Ascaris infection, most likely due to inadequacies in choice of population, sample size, experimental design, data analysis and/or relative failure of drug treatment. Field studies which attempt to measure the magnitude of growth deficits due to Ascaris must take the following into account: (1) rapidly growing preschool age children from communities with a high prevalence of protein-energy malnutrition are the most important group to study. (2) A longitudinal design, preferably using randomly allocated treatment and placebo groups, is highly desirable. (3) A sufficient period of time for growth improvement must be allowed between the beginning of the intervention and final measurements. (4) The sample sizes necessary to test hypotheses adequately should be calculated in advance. (5) The drug chosen for treatment of Ascaris should produce high cure rates and reinfection rates should be determined. Possible effects of the drug on other diseases prevalent in the population should be considered in the data analysis. (6) Evaluation of worm loads are very important in interpretation of results. (7) The data analysis must be appropriate for the individual study and must be designed to consider confounding factors. The economic implications of an infection like Ascaris are important aids to decision-making by government and health planners. The expenditures caused by Ascaris infection include: (A) health care system costs (patient care and drugs) and (B) family costs (retail purchase of drugs, lost wages and transport costs and food unabsorbed due to Ascaris infection). The costs and benefits of various types of Ascaris control programs and the difficulties of determining these are also discussed.