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Nursing homes are now recognized as niduses of infection with SARS-CoV-2. On February 29, 2020, because of known COVID-19 in their area, a nursing home in King County, Washington, instituted enhanced infection control measures and soon identified a resident and staff member who were infected. This prompted a larger study culminating in two point-prevalence surveys of the residents. Full-time staff were also tested.
On the initial screen of 76 residents, 23 (30%) were positive on nasopharyngeal swab for SARS-CoV-2. Among those testing positive, 12 (52%) were asymptomatic. One week later, 49 who were initially negative were retested. Of these, 24 (49%) were positive and 15 (63%) were without symptoms. Of the 27 residents testing positive without symptoms, 24 (89%) later developed symptoms. Among 138 full-time staff, 26 (19%) tested positive. The doubling time of infection was 3.5 days. Fifteen residents (26%) died. There was no difference in the viral load of SARS-CoV-2 in samples from those with symptoms and those without symptoms. Viable virus was isolated from 6 days before to 9 days after symptoms developed.
Arons MM et al. Presymptomatic SARS-CoV-2 infections and transmission in a skilled nursing facility. N Engl J Med 2020 Apr 24; [e-pub]. (https://doi.org/10.1056/NEJMoa2008457)
Gandhi M et al. Asymptomatic transmission, the Achilles' heel of current strategies to control Covid-19. N Engl J Med 2020 Apr 24; [e-pub]. (https://doi.org/10.1056/NEJMe2009758)
Comment
This paper has multiple important takeaways. First, infection can spread rapidly and efficiently in a nursing home environment. Second, infection control methods that focus only on those with symptoms are inadequate, since there is likely ongoing transmission from patients without symptoms as well as from staff. As the editorialists point out, this asymptomatic transmission distinguishes SARS-CoV-2 from the related SARS-CoV-1. Last, early and repeated viral testing of residents and staff, particularly those without symptoms, is the key to control.