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Symptom screening is of limited use in identifying cases of COVID-19, so mitigation measures could be “instrumental” in preventing an outbreak in independent living and assisted living communities, according to research published Friday by the Centers for Disease Control and Prevention.

Researchers from the CDC and UW Medicine tested 80 residents and 62 staff members of a Seattle-area independent living and assisted living community, and residents and staff also completed questionnaires, on March 10 and 11. The timeframe was a few days after two residents were hospitalized with confirmed cases of the disease and the community put social distancing and other preventive measures in place.

SARS-CoV-2, the virus that causes COVID-19, was detected in three residents and two staff members. None of the residents with positive tests had reported symptoms when the tests were given, but one had reported having some symptoms during the preceding two weeks. Both staff members with positive tests had reported symptoms. One asymptomatic resident who had tested negative during the first round of testing had a positive result during testing a week later.

COVID-19 symptoms were reported by 42% of residents and 25% of staff members who tested negative for the virus.

“[T]he high percentage of both residents and staff members who had negative test results for SARS-CoV-2, yet reported symptoms, illustrates the limitations associated with COVID-19 case identification strategies determined by presence of symptoms alone,” the study authors said. “The findings from this investigation underscore the importance of SARS-CoV-2 mitigation measures, including social distancing, visitor restriction, resident and staff member testing, exclusion of ill staff members, and enhanced disinfection and hygiene practices, which are consistent with current CDC guidance for preventing transmission of COVID-19 in independent and assisted living communities.”

That only four residents had positive test results “differed markedly” from the experiences of two Seattle skilled nursing facilities, where high COVID-19 transmission, morbidity and mortality was seen, the researchers noted.

“Possible explanations for differences in findings in this residential community from those in SNFs include more social distancing among residents and less contact with health care providers in independent and assisted living communities than that in SNFs,” the authors said. “In addition, early implementation of stringent isolation and protective measures after identification of two COVID-19 cases might have been effective in minimizing spread of the virus.”

The study, “Detection of SARS-CoV-2 Among Residents and Staff Members of an Independent and Assisted Living Community for Older Adults — Seattle, Washington, 2020,” was published in the April 3 issue of “Morbidity and Mortality Weekly Report.”