Arons MM, Hatfield KM, Reddy SC, et al. Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility. N Engl J Med. April 2020:NEJMoa2008457. doi:10.1056/NEJMoa2008457

The study:

This study reports the findings of an investigation into an outbreak of COVID-19 in a skilled nursing facility in the state of Washington (a preliminary report had been published on 27 March; a report on an outbreak in a separate nursing home in the same county was also recently published and summarised on LTCcovid.org).

The outbreak investigation started after first a member of health care staff, and two days later a hospitalised resident tested positive for SARS-CoV-2. 10 days after the first resident had tested positive, all 89 residents who were living in the nursing home when the first case was diagnosed were offered testing and were assessed for symptoms. A second round of testing was conducted one week later among residents who had tested negative or were asymptomatic during the first screening.

Key Findings:

• 64% of residents who were living in the nursing home at the time of the first diagnosis tested positive for SARS-CoV-2 within 23 days.
• Of those testing positive, 56% were asymptomatic (35% reported typical symptoms and 8% atypical symptoms). 89% of asymptomatic residents developed symptoms within a week after testing positive. 
• Within one month of the detection of the first case, 19% of the 57 residents with a COVID-19 diagnosis were in hospital (including 3 cases in intensive care) and 26% had died.  
• Among full-time staff members at the nursing home, 40% had reported symptoms within 23 days of the first confirmed case of a resident, and 19% tested positive for SARS-CoV-2. No staff member had been hospitalised.
• Laboratory tests showed similar viral loads for SARS-CoV-2-positive residents, regardless of whether they showed symptoms or not.

Meaning:

Despite infection control measures being put in place after the first resident was diagnosed with COVID-19, almost two thirds of residents had a confirmed COVID-19 diagnosis within three weeks. Infection control strategies that are solely based around symptoms may be inadequate given a high rate of asymptomatic cases and their potential for viral shedding. The authors suggest to instead consider testing-based strategies, which would allow more effective isolation of cases.   

Study limitations reported by the authors:

The potential for misclassification of symptoms was acknowledged. Further, this was a study among residents of a skilled nursing facility, with potentially limited generalisability to the general public. Finally, the role of asymptomatic members of staff in this outbreak was not investigated.

Summary by Maximilian Salcher-Konrad (CPEC-LSE)