Almost two months after the first case of COVID-19 was confirmed in a nursing home, a new study confirms what several others have indicated: People infected with COVID-19 can contribute to transmission of the illness without showing any symptoms.
The most recent findings on the asymptomatic spread of the virus in nursing homes, published online on April 24 in the New England Journal of Medicine (NEJM), echo those of the Centers for Disease Control and Prevention (CDC), which in March determined residents without symptoms can spread COVID-19.
“More than half of residents with positive test results were asymptomatic at the time of testing and most likely contributed to transmission,” the NEJM authors — which include the CDC’s COVID-19 Investigation Team — wrote in the NEJM study. “Infection-control strategies focused solely on symptomatic residents were not sufficient to prevent transmission after SARS-CoV-2 introduction into this facility.”
The NEJM report examined a facility in King County, Wash. — different from the Life Care Center of Kirkland, where the first major COVID-19 outbreak was reported.
The 116-bed facility described in the NEJM had its first positive COVID-19 test in a resident on March 3. Asymptomatic residents were defined as those having either no symptoms or stable chronic symptoms, such as a chronic cough that did not get worse; pre-symptomatic residents were those who were asymptomatic at the time of testing but developed symptoms within a week of the test.
If residents had at least one new or “worsened” typical or atypical symptom of COVID-19 in the preceding 14 days, they were classified as symptomatic, according to the study.
“Of the 48 residents who tested positive from the surveys, 17 (35%) reported typical symptoms, 4 (8%) reported only atypical symptoms, and 27 (56%) reported no new symptoms or changes in chronic symptoms at the time of testing,” the authors wrote. “Among the 27 residents classified as asymptomatic, 15 reported no symptoms and 12 reported only stable chronic symptoms.”
But a week after their positive tests, 24 out of the 27 asymptomatic residents had an onset of symptoms and were then recategorized as pre-symptomatic; the median time of symptom onset was four days.
“Although we are unable to quantify the contributions of asymptomatic and presymptomatic residents to transmission of SARS-CoV-2 in this facility, evidence suggests that these residents had the potential for substantial viral shedding,” the authors wrote.
Specifically, droplet and possibly aerosol transmission might have resulted from the shedding of high viral titers — defined as “the concentration of a substance in a given sample as determined by titration” — from the respiratory tract, including before the symptoms got started, the study authors said.
This means residents and staff members with undetected infection likely contributed to the spread of COVID-19; though the role of indirect contact wasn’t as clear, contaminated surfaces and shared medical devices might also have led to problems, the authors said.
This could help explain why outbreaks at nursing facilities have continued to grow across the country, despite the Centers for Medicare and Medicaid Services (CMS) officially banning most visits to SNFs in the middle of March and nursing home associations such as the American Health Care Association (AHCA) recommending screening visitors and staff for symptoms around the same time.
“Current interventions for preventing SARS-CoV-2 transmission in health care settings rely primarily on the presence of signs and symptoms to identify and isolate residents and staff who might have Covid-19,” they wrote. “The data presented here suggest that sole reliance on symptom-based strategies may not be effective to prevent introduction of SARS-CoV-2 and further transmission in skilled nursing facilities.”
Because of the potential for asymptomatic or pre-symptomatic transmission playing a key role in the SNF setting, other preventions should be considered. Those might include using testing to guide use of transmission-based precautions, isolation and cohorting.
“Once SARS-CoV-2 has been introduced, additional strategies should be implemented to prevent further transmission, including use of recommended personal protective equipment, when available, during all resident care activities regardless of symptoms,” the authors wrote. “Consideration should be given to test-based strategies for identifying residents and staff with SARS-CoV-2 infection for the purpose of excluding infected staff and cohorting residents, either in designated units within a facility or in a separate facility designated for residents with COVID-19.”