Does Asymptomatic Transmission Accelerate COVID-19 Spread in Nursing Homes?

April 28, 2020

Over half of residents with positive test results were asymptomatic at the time of testing, during a recent survey.

Public health officials in the US anticipated that SARS-CoV-2 infection would be more severe in older adults, based on data from countries like Italy which experienced earlier outbreak onsets. But have interventions sufficiently shielded the nursing home setting?

The investigators of a recent study published in The New England Journal of Medicine detailed the rapid spread of coronavirus disease 2019 (COVID-19) through a skilled nursing facility, finding that over half of residents with positive test results were asymptomatic at the time of testing.

The nursing home monitored through the study is a 116-bed facility divided with both short- and long-term residents mixed throughout 4 units.

The study team conducted 2 serial point-prevalence surveys for SARS-CoV-2 in which they administered nasopharyngeal and oropharyngeal swab testing to volunteers. Tests were performed 1 week apart.

Methods included real-time reverse-transcriptase polymerase chain reaction tests (PCRs), sequencing, and viral culture. Symptoms within the previous 14 days were recorded.

Residents were categorized based on whether they displayed typical symptoms (cough, fever, shortness of breath), displayed atypical symptoms, were pre-symptomatic, or were asymptomatic.

By 23 days after the first positive test result at the nursing home, 57 out of 89 total residents (64%) tested positive for SARS-CoV-2.

Out of 76 residents who participated in the point-prevalence surveys, 48 (63%) had positive test results. Out of these 48 residents, 27 (56%) were classified as asymptomatic at the time of testing, but 24 of the 27 residents developed symptoms with a median time to onset of 4 days.

Samples from the 24 pre-symptomatic residents had a median PCR cycle threshold value of 23.1. Viable virus was recovered from 17 of the residents. Out of 34 residents who had specimens which underwent sequencing, 27 (79%) had sequences which fit into 2 clusters, with a difference of 1 nucleotide.

At the time of publication, 15 residents had died and 11 residents had been hospitalized. Out of these 11 hospitalized residents, 3 were admitted to the intensive care unit.

“Rapid and widespread transmission of SARS-CoV-2 was demonstrated in this skilled nursing facility," investigators wrote. "Infection-control strategies focused solely on symptomatic residents were not sufficient to prevent transmission after SARS-CoV-2 introduction into this facility."

As calls for increased testing capacity continue to go unanswered, studies like these may shine a light on high priority outbreak hotspots where directing presently limited testing resources may be most valuable.

“The ability to test large numbers of residents and staff with rapid turn-around times may expedite cohorting of residents and staff in locations designated for the care of those with SARS-CoV-2 infection either in different locations within individual facilities or in separate facilities,” the investigators wrote.