The effect of previous Giardia infection on the presentation of new Giardia infections among children in Bangladesh.

Thesis (Master's)--University of Washington, 2015Background: Giardia Lamblia (Giardia) is considered to be pathogenic in high-resource settings, but observational studies among children in resource-limited settings suggest an inverse relationship between Giardia and diarrhea. To test the hypothesis that an adaptive immune response prevents diarrhea in Giardia infections following a child’s first exposure, we examined the association between first (compared to subsequent) Giardia infections and diarrhea among Bangladeshi children in their first two years of life. Methods: Children were followed from birth to two years with bi-weekly home visits and stool was collected from children monthly and during episodes of diarrhea. Children with less than two unique Giardia infections were excluded from the primary analysis. The odds of diarrhea at a child’s first Giardia detection was compared to the odds of diarrhea at presentation of subsequent Giardia infections using Generalized Estimated Equations with an independent correlation structure. Breast feeding, age, nutritional status, maternal education and head of household education were considered potential confounding factors and maintained in the logistic regression model if their inclusion changed the odds ratio by more than 10%. Results: Among 265 children enrolled in the parent study, the mean birth weight at enrollment was 2.8 kg (standard deviation [SD]=0.4kg) and exclusive breastfeeding was maintained for an average of 4.8 months (SD = 1.8 months). The incidence rate of Giardia infection was 30.6 per 1000 child months and 32.7% of all giardia infections were first detected in diarrheal stool. Forty children had at least two unique Giardia infections, and adjusting for head of household education and age of the child, the odds of diarrhea was not significantly different between first and subsequent Giardia infections (OR 1.22, 95% CI: 0.42 to 3.54, p-value: 0.71). Conclusion: We did not find significant evidence to suggest that diarrhea was more common in children with a first episode of Giardia. However, the analysis may have been underpowered to detect smaller odds ratios than we observed. Future studies that include more frequent sampling of asymptomatic children, molecular diagnostics, and a larger sample size of multiply infected children are needed to explore this hypothesis further