Laboratory-confirmed acute gastroenteritis surveillance in the United States showed a dynamic intra- and interannual prevalence and incidence variability of outpatient and inpatient community‑acquired norovirus among veterans, according to a study recently published in Clinical Infectious Diseases.

Acute gastroenteritis is a major cause of morbidity in the US with an estimated 179 million cases, more than 1 million hospitalizations, and more than 11,000 deaths annually. The leading cause of acute gastroenteritis is norovirus. However, prior estimates of norovirus acute gastroenteritis in adults in the US have been based both on studies in other developed countries and on passive surveillance. To assess the potential effects of targeted inventions, such as a norovirus vaccine candidate, direct assessments of age-specific norovirus incidence are needed. Therefore, this multiyear analysis study estimated the prevalence and incidence of outpatient and inpatient community-acquired norovirus acute gastroenteritis at 4 Veterans Affairs Medical Centers from 2011 to 2015.

In total, 1603 stool samples were collected within 7 days of acute gastroenteritis symptom onset. Samples were tested for norovirus, and positive samples were genotyped. Incidence was then calculated by multiplying norovirus prevalence in tested specimens by acute gastroenteritis-coded outpatient encounters

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Of 1603 stool specimens, 6% were positive for norovirus; the most common genotypes were GII.4 viruses: 17% were GII.4 New Orleans genotype and 47% were GII.4 Sydney genotype. Norovirus incidence was higher in outpatients than inpatient community-acquired incidence. Results showed that the overall prevalence of inpatient and outpatient community-acquired incidence followed a seasonal pattern in which higher median rates were observed during the months of November to April (9.2%), and lower rates were observed between the months of May and October (3.0%). Further, results also showed an alternate-year pattern, with the highest peak of prevalence of inpatient and outpatient community-acquired incidence in the first and third years of surveillance (14%-25%).

Overall, the study authors concluded that, “Ongoing surveillance is needed to further characterize temporal trends identified during passive surveillance, and will allow for refinement of norovirus incidence estimates.”

Reference

Grytdal S, Browne H, Collins N, et al. Trends in incidence of norovirus-associated acute gastroenteritis in four veterans affairs medical center populations in the United States, 2011-2015 [published online March 1, 2019]. Clin Infect Dis. doi:10.1093/cid/ciz165/5367395