More than half who tested positive had no symptoms

In a Seattle-area nursing home that was hit with an early outbreak of Covid-19 cases, more than half of the residents who tested positive for SARS-CoV-2 were asymptomatic at the time of testing, and they most likely contributed to transmission of the virus, researchers found.

Twenty-three days after the first SARS-CoV-2 infection was identified at the facility, 57 (64%) of the 89 residents tested positive for Covid-19 — fifteen (26%) of whom died of the illness — and 19% of staffers had been diagnosed with the coronavirus, researchers with the CDC and Seattle and King County Health Departments reported.

Of the 76 residents of the nursing home who participated in point-prevalence surveys, 48 (63%) tested positive; of the 48 who tested positive, 27 (56%) were asymptomatic at the time of testing.

Twenty-four subsequently developed symptoms, with the median time to symptom onset of 4 days.

Specimens from these 24 viral-positive patients who were pre-symptomatic at testing (71%) had viable virus culture 1 to 6 days before developing symptoms.

And, viral loads among residents testing positive were similar among those with typical and atypical symptoms of SARS-CoV-2 infection and those who never developed symptoms at all, according to researcher Melissa M. Arons, RN, of the CDC’s Covid-19 Investigation Team, and colleagues, whose study was published April 24 in New England Journal of Medicine.

“Transmission from asymptomatic residents infected with SARS-CoV-2 most likely contributed to the rapid and extensive spread of infection to other residents and staff,” wrote Arons and colleagues.

In a telephone interview with BreakingMED, infectious disease specialist Monica Gandhi, MD, of the University of California, San Francisco, said symptom-based screening alone was clearly not enough to control transmission in this nursing home, where 1 in 4 infected residents died.

“The truly alarming things about this were the high percentage of people who tested positive with no symptoms and the fact that these asymptomatic people were shedding virus at the same rate as those who were highly symptomatic,” she said.

In an editorial published with the study, Gandhi and UCSF colleagues Deborah Yoke, MD, and Diane Havlir, MD, called for greatly expanding Covid-19 testing in skilled nursing homes across the U.S. to include asymptomatic people living and working in the facilities.

“Despite ’lockdowns’ in these facilities, coronavirus outbreaks continue to spread, with 1 in 10 nursing homes in the United States (>1,300 skilled nursing facilities) now reporting cases, with the likelihood of thousands of deaths,” they wrote.

They called for routine real-time reverse transcriptase PCR (rRT-PCR) testing, along with symptomatic screening of new residents before entry, as well as “conservative guidelines for discontinuation of isolation, and periodic retesting of long-term residents, as well as both periodic rRT-PCR screening and surgical masking of all staff.”

Gandhi told BreakingMED that this aggressive testing approach is necessary not only in nursing homes, but in other congregant living spaces, including jails and prisons, homeless shelters, hospitals, and mental health living facilities.

Everyone who works at one of these centers should be tested at least once a week, she said, and residents should also be tested periodically, whether or not they have symptoms.

“All of these recommendations make the assumption that these tests are readily available, and that hasn’t happened yet,” she said. “We need massive testing, we need contract tracing, and we need to isolate and quarantine, but we haven’t managed to do it.”

In their effort to evaluate the impact of symptom-based screening in the Seattle-area nursing home, Arons and colleagues conducted two serial point-prevalence surveys, 1 week apart, which included resident of the nursing home who agreed to nasopharyngeal and oropharyngeal testing for SARS-CoV-2, including rRT-PCR, viral culture, and sequencing.

Symptoms that were identified during the previous 14 days were recorded and asymptomatic residents who tested positive were reassessed 7 days later.

Those testing positive were categorized as having typical symptoms (fever, cough, or shortness of breath) or atypical symptoms and as pre-symptomatic or asymptomatic.

All symptomatic health care workers were advised get tested by their health care provider, and asymptomatic staff members were not tested as part of this investigation.

Samples from the 24 pre-symptomatic residents had a median rRT-PCR cycle threshold value of 23.1, and viable virus was recovered from 17 residents.

The study authors sequenced specimens from 34 residents, and all sequences were identical or highly similar to sequences reported in a previous analysis of Covid-19 cases in Washington state. Twenty-seven (79%) of the 34 residents had sequences that fit into two clusters with one nucleotide difference.

The researchers wrote that “symptom-based infection-control strategies were not sufficient to prevent transmission after the introduction of SARS-CoV-2 into this skilled nursing facility.”

  1. More than half of residents of a Seattle-area nursing home with an early outbreak of Covid-19 cases who tested positive for SARS-CoV-2 were asymptomatic at the time of testing.

  2. Viral loads among residents testing positive were similar among those with typical symptoms and atypical symptoms of SARS-CoV-2 infection and those who never developed symptoms at all.

Salynn Boyles, Contributing Writer, BreakingMED™

This research was conducted by researchers from Public Health-Seattle and King County and the CDC’s Covid-19 Investigation Team.

The researchers reported no funding source, and they disclosed no relevant relationships with industry related to this study.

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