LAUSR

BACKGROUND: Coinciding with the COVID-19 pandemic, global influenza virus circulation decreased, possibly due to widespread community mitigation measures. Cambodia eased some COVID-19 mitigation measures in June and July 2020. On Aug 20th a cluster of respiratory illnesses among residents of a pagoda included persons that had tested positive for influenza A, and none that were positive for SARS-CoV-2. METHODS: On Aug 25, a response team deployed. Persons with influenza-like illness (ILI) were asked questions on demographics, illness, personal prevention measures, and residential arrangements. Respiratory swabs were tested for influenza and SARS-Cov-2 by RT-PCR; viruses were sequenced. Sentinel surveillance data were analyzed to assess recent trends in influenza circulation in the community. RESULTS: Influenza A(H3N2) viruses were identified in sentinel surveillance in Cambodia in July 2020, prior to the reported pagoda outbreak. Among the 362 pagoda residents, 73(20.2%) ILI cases were identified; 40 were tested with 33/40 (82.5%) confirmed positive for influenza A(H3N2). All 40 were negative for SARS-CoV-2. Among 73 residents with ILI, none were vaccinated against influenza, 47 (64%) clustered in 3 of 8 sleeping quarters; 20 (27%) reported often wearing a mask; 27 (36%) reported often washing hands; and 11 (15%) reported practicing social distancing. All viruses clustered within clade 3c2.A1 close to strains circulating in Australia in 2020. CONCLUSIONS: Circulation of influenza viruses began in the community following a relaxing of national COVID-19 mitigation measures, and prior to this outbreak in a pagoda with limited social distancing. Continued surveillance and influenza vaccination remain needed to limit the impact of influenza globally.