By age 2, nearly all children in a US birth cohort had contracted an enteric viral infection, most of which presented asymptomatically, a recent study in Pediatrics found.

Norovirus GII and sapovirus emerged as the high-burden enteropathogens for acute gastroenteritis.

“The study enhances our understanding of the epidemiology, symptoms, and disease burden of enteric viral pathogens, providing a broader perspective on the range of symptoms in early childhood,” said Jan Vinjé, PhD, lead of the Norovirus Laboratory Team at the CDC in Atlanta, who helped author the study.

In the US, vaccines have contributed to an 80% reduction in hospitalizations due to rotavirus, but the relative burden of norovirus and other enteric viral pathogens has increased, Vinjé said.

The PREVAIL cohort study, conducted in Cincinnati, asked mothers to collect weekly stool samples from their 245 babies and complete symptom surveys in order to establish community-level prevalence of the viruses in the first 2 years of life. Additional stool samples were requested when symptoms were present, with testing for five viral pathogens.

Of the dyads, 41% were characterized as adherent, which was defined as submitting at least 70% of weekly stool specimens with at least 18 months of follow-up. The remaining dyads were defined as less adherent.

By age 2, 90% of children had at least one enteric viral infection. In total, 904 enteric viral infections were identified, 25% of which were symptomatic, 63% were asymptomatic, and 12% were of unknown status.

The highest incidence of symptomatic infection was for norovirus GII (0.4 per child-year) and sapovirus (0.2 per child-year), followed by astrovirus, rotavirus, norovirus GI, and adenovirus.

Incidence rates for viral infections and symptomatic infection were 3.8 and 0.9 per child-year, respectively.

Among symptomatic infections, only 35% were medically attended. Symptomatic infections were more frequent after age 6 months.

Overall, 64% of single-pathogen infections were asymptomatic, and 90% were not medically attended, with only 24% treated by home care, according to the researchers. Asymptomatic infections were frequently detected before age 6 months.

“Asymptomatic infections were more common, but the extent of their role in transmission is unclear,” Vinjé said.

Robert L. Atmar, MD, infectious disease specialist in the Department of Medicine at Baylor College of Medicine in Houston, said the findings were not surprising. The rates of rotavirus are much less now than before the introduction of the vaccine in the US. But the rates of subclinical infection were notable, he said.

“It’ll be important to perform future studies to understand why this happens,” Atmar said.

The data also underscore the burden of sapoviruses, “whose impact has arguably been relatively underappreciated in the US despite their prevalence in medically attended [acute gastroenteritis] in children,” wrote Natasha Makabilo Laban, PhD, research associate in the Centre for Infectious Disease Research in Zambia, Africa, and Benjamin Leeb, MD, pediatric infectious disease specialist at Larner College of Medicine at the University of Vermont in Burlington, Vermont, in an editorial accompanying the journal article.

Ongoing studies using the cohort are investigating long-term responses to rotavirus vaccination, wild-type infection, and host-specific factors influencing immunity, Vinjé said.

The study was funded through a cooperative agreement from the CDC, the Influenza IMPRINT Cohort, and the University of Cincinnati and Cincinnati Children’s Hospital Medical Center, Cincinnati, among others. The editorial authors reported receiving no funding. Various study authors reported having contracts or consulting work for Merck, Cepheid, and Moderna, among others. 

Diana Swift is a freelance writer.