A study of a King County nursing home shows just how insidious an outbreak of the novel coronavirus can be, federal investigators said Friday.
The study looked at one unnanmed nursing home where an outbreak of the virus was suspected earlier this month.
It found that more than half of people who tested positive for the virus had no symptoms at the time.
On March 13, investigators with the Centers for Disease Control and Prevention tested 76 residents of the unnamed nursing home for the coronavirus.
A few residents of the facility had started getting sick after a worker tested positive for the virus on March 1, the CDC said.
(The nursing home was not Life Care Center in Kirkland, where the nation's first known outbreak of the novel coronavirus has killed at least 37 people, according to the study. Multiple nursing homes in the area have had outbreaks of COVID-19.)
When results came back, 23 residents tested positive for the virus. But 13 of them had none of the telltale signs of COVID-19: fever, coughing, and shortness of breath.
That meant a majority of residents carrying the virus — 57 percent — were "asymptomatic."
The results suggest that screening for symptoms of COVID-19 may miss a large number of cases. Many health care providers look for telltale signs of the disease before adminstering a test.
"Symptom-based screening in (nursing homes) could fail to identify approximately half of residents with COVID-19," the CDC said in its report.
The study also is further evidence that people who don't have symptoms of the novel coronavirus may play an unseen role in spreading it. It helps explain how nearly a third of the nursing home's residents contracted the virus, even though workers quickly adopted prevention measures such as isolating patients with symptoms and wearing protective gear when entering those patients' rooms, the CDC said.
Ten of the 13 asymptomatic patients ended up showing symptoms within a week of testing positive, the CDC said.
