Vitamin A supplementation has divergent effects on norovirus infections and clinical symptoms among Mexican children

Background. The effect of vitamin A supplementation on viral gastrointestinal infections among young children living in developing countries remains unclear. Methods. The effect of vitamin A supplementation on norovirus (NoV) infection among 127 Mexican children 5-15 months of age was studied in a randomized, placebo-controlled trial during June-August 1998. Stool samples collected every 2 weeks and after diarrheal episodes were screened for NoV and characterized at the genogroup level (GI and GII). Results. Of the stool samples collected, 29.9% were positive for NoV, and NoV GI and NoV GII were found in 55.4% and 46.4% of the positive samples, respectively. Vitamin A supplementation reduced the prevalence of NoV GII infections (rate ratio [RR], 0.60 [95% confidence interval {CI}, 0.20-0.82]), increased the length of both NoV GI and GII shedding, and decreased the prevalence of NoV-associated diarrhea (RR, 0.51 [95% CI, 0.26-0.97]). Conclusions. These findings suggest that NoV is an important cause of pediatric diarrhea in this study population and that vitamin A supplementation has divergent effects on specific outcomes of NoV infection.