Measures to combat COVID-19 cause sharp decline in norovirus
Between April and July last year, there was a more than 80% decline in the incidence of reported norovirus outbreaks in nine U.S. states, likely the result of nonpharmaceutical interventions to combat COVID-19, researchers reported.
“We noticed in spring of 2020 that there was a major drop in the number of norovirus outbreaks reported to NoroSTAT” — a network of 12 states that report norovirus outbreaks to the CDC — “much larger and sooner than we would typically expect for that time of year,” Alicia N.M. Kraay, a postdoctoral fellow at the Emory University Rollins School of Public Health, told Healio.
“We wondered if this could be related to the nonpharmaceutical interventions being implemented for COVID-19”— such as social distancing, mask wearing and increase hand hygiene — “and decided to do a study to investigate this hypothesis while also accounting for seasonality and seeing if underreporting was a more likely explanation,” Kraay said.
Kraay and colleagues assessed data from nine of the 12 NoroSTAT states from July 2012 through July 2020 to determine if the decline was best explained by underreporting, seasonal trends or reduced exposure due to nonpharmaceutical interventions (NPIs) implemented for the pandemic.
Overall, the study showed a “dramatic” decrease in norovirus incidence and outbreak size 86% and 61%, respectively starting in April 2020. According to the study, these decreases did not appear to be primarily caused by underreporting or seasonality. Kraay said they assessed the combined impact of all NPIs in the study and determined that reductions in incidence were least pronounced in nursing homes and health care facilities which stayed open amid the pandemic leading the team to believe that the primary initial driver of declines was closing venues where transmission commonly occurs, such as schools and universities.
According to Kraay, researchers are in the process of a follow-up analysis to study how the relaxation of certain NPIs affects norovirus incidence, and to provide additional data on which interventions were most responsible for the decline.
“Nonpharmaceutical interventions initially implemented to reduce COVID-19 transmission appear to have had the indirect benefit of reducing the incidence of norovirus, a nonrespiratory pathogen,” Kraay said. “These benefits illustrate the far-reaching importance of NPIs and suggest that these indirect benefits may have helped reduce health system strain during the fall/winter 2020 surge. These benefits continue to be helpful as we continue to work to control the pandemic.”