Norovirus wastewater monitoring during a community outbreak investigation in Pennsylvania.

Norovirus is a leading cause of acute gastrointestinal illness (AGI). Norovirus is not notifiable in the United States; therefore, health departments typically only receive reports of norovirus outbreaks. While wastewater surveillance has been demonstrated to be useful for tracking community norovirus case reports, its value during outbreak investigations is less understood. This study evaluates the impact of a single norovirus outbreak on wastewater measurements in a community. Norovirus genogroup 2 (GII) concentrations were measured at two wastewater treatment facilities (WWTFs) near a restaurant experiencing a norovirus GII outbreak (Restaurant A). The largest increase in norovirus GII RNA concentrations (increase of 13,111.8 gc/mL) at the WWTF serving Restaurant A (WWTF A) occurred on the same day most (44%) outbreak case patients reported symptom onset. This increase occurred 1 day before the outbreak was reported to public health, 2 days before norovirus was identified in clinical specimens, and 3 days before clinical specimens were genotyped at the public health laboratory. At a second local WWTF, WWTF B, norovirus GII RNA concentrations also increased at the same time but peaked 2 days after WWTF A. These findings suggest wastewater measurements can serve as a leading indicator of norovirus outbreaks and inform outbreak response efforts.