COVID-19: Asymptomatic COVID-19 casesStudy: Many Asymptomatic COVID-19 Cases Undetected
More than half of residents of a Seattle-area nursing home had no symptoms when they tested positive for COVID-19 and had probably already spread the disease, according to a new study. “Our data suggest that symptom-based strategies for identifying residents with SARS-CoV-2 are insufficient for preventing transmission in skilled nursing facilities,” the researchers wrote. “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.”
More than half of residents of a Seattle-area nursing home had no symptoms when they tested positive for COVID-19 and had probably already spread the disease, according to a study published late last week in the New England Journal of Medicine (NEJM).
Also, a study in Emerging Infectious Diseases (EID) found that all five household contacts of a mildly symptomatic doctor in Wuhan, China infected with the novel coronavirus had the disease but no symptoms.
Shortcomings of Symptom-Based Screening, Cohorting
In the NEJM study, officials with Public Health–Seattle and King County and the Centers for Disease Control and Prevention conducted two serial point-prevalence surveys 10 and 17 days after an outbreak was identified at the nursing home in early March.
The nursing home is in King County but is not the Life Care facility in Kirkland that was one of the first US hot spots for the novel coronavirus.
Fifty-seven (64 percent) of 89 residents in this second nursing home tested positive for COVID-19. Of the 76 residents who participated in the surveys, 48 (63 percent) tested positive. Twenty-seven (56 percent) of the 48 had no symptoms when tested, and 24 of them later had symptoms within a median of 4 days.
Seventeen (35 percent) reported typical symptoms such as fever, cough, and shortness of breath, and four (8 percent) reported only atypical symptoms, such as chills, malaise, confusion, nasal discharge or congestion, sore throat, muscle pain, dizziness, headache, nausea, or diarrhea.
Live virus was recovered from 17 presymptomatic residents (71 percent) 1 to 6 days before symptom onset. Similarly high viral loads were found in all residents with confirmed disease, regardless of whether they had symptoms and whether their symptoms were atypical.
CIDRAP notes that the authors estimated an infection doubling time of 3.4 days, compared with 5.5 days in the surrounding community. Because patients who tested negative often had typical symptoms, the rapid speed of transmission could have been partly due to symptom-based cohorting strategies that could have inadvertently spread SARS-CoV-2, the virus that causes COVID-19, to uninfected residents.
As of Apr 3, 11 of the infected patients had been hospitalized (3 in the intensive care unit), and 15 had died, a death rate of 26 percent, despite early implementation of infection-control procedures. Twenty-seven (79 percent) of the 34 residents with sequenced specimens were identified as being part of two clusters of cases.
