Reviewed by Sanchi Malhotra MD, University of California Los Angeles
The New Vaccine Surveillance Network is a pediatric surveillance system that had previously identified children who were hospitalized or seen in the ED for acute gastroenteritis (AGE). This data set was previously used to understand household transmission of rotavirus and now the same principles are being applied to understand household transmission of norovirus. Previous studies estimate a norovirus secondary attack rate of 15-30%.
Authors surveyed households where the child age 14 days to 11 years old was the index case, excluding households with contacts who had AGE symptoms the week prior or the same symptom onset date as the child. Household transmission was defined as having AGE symptoms 1-7 days after the child or another household contact (HHC). Households had to complete the survey 7-35 days after enrollment and children had to have had a norovirus test result. Norovirus testing was largely done via dedicated PCR or part of a pathogen panel.
Of the index cases presenting to the ED/hospitalized for AGE, 22% had norovirus. Norovirus positive children tended to be younger, more likely to be Hispanic, and were more likely to be from smaller households or households without other children.
Households with norovirus index cases were more than twice as likely to have at least one household contact affected compared to children with norovirus negative AGE episodes (32.6% vs 15.4%; OR 2.66), and more household contacts tended to be affected (16.7 vs 6.2%, OR 3.02). Household contacts of norovirus cases were less likely to seek medical care (17.6% vs 27.5%, p<0.05).
Most notably, the index case having > 5 episodes of vomiting in a 24-hour period was associated with the greatest odds of transmission. Household contacts who were age 0-4 had higher attack rates, however most contacts (61%) were aged 18-49. Interestingly, households that had higher household income, and fewer household members had significantly higher attack rates.
Parents/caregivers were 90% of ill adult HHCs likely due to significant contact with the index case which may be difficult to avoid as they were young children and had severe enough illness to present to the ED.
Of note, stool was not collected from HHCs so transmission estimates were only based on symptomatology. Additionally, one parent/guardian was surveyed, raising the potential for misreporting and recall bias.
A large limitation is that this study enrolled patients only from the ED or hospitalization, and therefore from index patients who may have had more severe disease. Therefore, this does not account for the many outpatient episodes of norovirus that occur in the community, and may not accurately represent norovirus attack rate.
Reference:
Moran MC, Wikswo ME, Selvarangan R, et al. Acute Gastroenteritis Among Household Contacts of Children with Severe Norovirus Gastroenteritis, United States, 2011–2016. J Pediatr Infect Dis Soc. 2025;14(6):piaf049. doi:10.1093/jpids/piaf049. Published June 16, 2025.