Norovirus-associated diarrhea and asymptomatic infection in children aged under 4 years: a community-cohort study in the Philippines

Abstract

Objectives

This study aimed to estimate the incidence of norovirus (NoV)-associated diarrhea and asymptomatic infections in children under 4 years of age and identify the genotypes of multiple NoV infections.

Methods

A community-based cohort study was conducted in Tarlac, Philippines. Children aged 0-2 years were followed up for 2 years. The prevalence and incidence rates of NoV-associated diarrhea and asymptomatic infections were calculated. Risk factors were assessed using the Cox proportional hazards model. The genotypes and immunotypes of repeated infections were tabulated.

Results

A total of 338 children aged 6208 child-months were analyzed. NoV was detected in 17.4% (84 of 527, 95% confidence interval [CI]: 12.7-19.7%) of diarrheal episodes and 10.8% (219 of 2031, 95% CI: 9.4-12.3%) of asymptomatic stool samples. The highest incidence of NoV-associated diarrhea occurred in children aged 6-11 months (2.31 per 100 child-months, 95% CI: 1.30-3.32) and 18-23 months (2.34 per 100 child-months, 95% CI: 1.57-3.12), whereas the highest incidence of asymptomatic NoV infection was observed in children aged 12-23 months (4.49 per 100 child-months, 95% CI: 3.41-5.56). Repeated NoV infections were detected between different genotypes, except in two children who had repeated NoV GI.3 and two children with GI.9 infections.

Conclusions

Children had the highest risk of NoV-associated diarrhea during their first year of life, whereas asymptomatic NoV infections persisted after the second year. Repeated NoV infections suggest genotype-specific immunity after NoV infection.