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Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility – King County, Washington, March 2020

Our take —

This study assessed residents of a long-term care skilled nursing facility for symptom presentation and biological testing for SARS-CoV-2. Through facility-wide testing, 30% of residents tested positive, among which more than half were asymptomatic at the time of testing. Additionally, testing for SARS-CoV-2 showed viral loads among asymptomatic, pre-symptomatic, and symptomatic residents did not differ, suggesting the potential for transmission regardless of symptoms, though the limited sample warrants caution. This study suggests syndromic methods for case identification and isolation of residents who might have SARS-CoV-2 is not sufficient to control for spread of infection.

Study design

Prospective cohort

Study population and setting

This study described symptom presentation and test results for SARS-CoV-2 infection among 76 residents within a long-term care skilled nursing facility in King County, Washington (note testing was not done for 6/82 residents, for various reasons, including 2 who were transferred to the hospital for presumed COVID-19 care). Nasopharyngeal swabs were used to collect biological samples from residents, and one-step real-time RT-PCR assay was performed on all specimens using the SARS-CoV-2 CDC assay protocol. A symptomatic screening tool was used to categorize patients as asymptomatic (no symptoms or only stable chronic symptoms) or symptomatic (at least one new or worsened typical or atypical symptom of COVID-19) on the day of testing or during the preceding 14 days; a follow-up symptom assessment was completed 7 days later.

Summary of Main Findings

Among the 76 tested residents, 23 (30.3%) had a positive test result for SARS-CoV-2. Among the 23 residents with positive test results, 10 (43%) had symptoms on the date of testing, while 13 (57%) were asymptomatic at the time of testing. Among those asymptomatic at the time of testing, 10 out of 13 went on to develop symptoms and were re-categorized as pre-symptomatic at the time of testing. Real-time RT-PCR Ct values for both genetic markers among residents with positive test results for SARS-CoV-2 did not show significant quantitative differences between the four symptom status groups (p = 0.3).

Study Strengths

A strength of this study was the methods for measurement including assessment of symptoms, biological testing for the presence of SARS-CoV-2 infection among both symptomatic and asymptomatic individuals, and the follow-up with individuals to assess for symptoms seven days after the initial test.


Approximately half of the study population had pre-existing cognitive impairment, which may have limited accurate symptom ascertainment. Results from this study may not represent younger persons, those without underlying medical conditions, or similarly aged populations in the general community. The number of cases were limited and thus comparisons of quantitative RT-PCR values across groups should be interpreted with caution.

Value added

This study assessed SAR-CoV-2 infection and viral load among individuals both with and without symptoms to demonstrate infection and potential infectiousness among those without symptoms. Longitudinal data from an outbreak site allows for study of both asymptomatic individuals and pre-symptomatic cases.