Reduction in Sporadic Norovirus Infections Following the Start of the COVID-19 Pandemic, 2019–2020, Philadelphia

INTRODUCTION: Norovirus infections are common in the USA and worldwide. Detection of norovirus in fecal samples is now common in routine tests for enteric pathogens using molecular methods. We observed a change in positivity rates for norovirus after the beginning of the coronavirus disease 2019 (COVID-19) pandemic in our laboratory and performed a more detailed analysis of testing results. METHODS: We reviewed the positivity rates for detection of common enteric pathogens from stool samples submitted to an academic medical center laboratory pre (2016–2019) and post the start of the COVID-19 pandemic (2020). RESULTS: In contrast to other enteric pathogens, norovirus positivity rates dropped dramatically from a yearly average of 3.9% in 2016–2019 to 0.76% from March 2020 through the end of 2020. CONCLUSION: A sustained reduction in norovirus positivity rates was temporally associated with COVID-19 mitigation processes in the Philadelphia area, while positivity rates for other common enteric pathogens were only intermittently reduced.