Twenty-three days after identifying the first resident with SARS-CoV-2 infection, Facility A had a 64% prevalence of Covid-19 among residents, with a case fatality rate of 26% despite early adoption of infection-control measures. In addition, Covid-19 was diagnosed in 26 members of the staff (19%). These findings are strikingly similar to descriptions of the first Covid-19 outbreak in a U.S. skilled nursing facility, which occurred in the same county at nearly the same time.2 In the investigation reported here, more than half of the residents with positive tests were asymptomatic at the time of testing. Transmission from asymptomatic residents infected with SARS-CoV-2 most likely contributed to the rapid and extensive spread of infection to other residents and staff. Symptom-based infection-control strategies were not sufficient to prevent transmission after the introduction of SARS-CoV-2 into this skilled nursing facility.

Although we are unable to quantify the contributions of asymptomatic and presymptomatic residents to transmission of SARS-CoV-2 in this facility, evidence suggests that these residents had the potential for substantial viral shedding. Ct values indicating large quantities of viral RNA were identified, and viable SARS-CoV-2 was isolated from specimens of asymptomatic and presymptomatic residents. Evidence of transmission from presymptomatic persons has been shown in epidemiologic investigations of SARS-CoV-2.12-14

We estimated that the doubling time in this facility was 3.4 days, which is faster than that of the surrounding community, 5.5 days. The accelerated doubling time was likely to have been due to inadequately controlled intrafacility transmission, which sequencing and spatiotemporal data suggest was the primary driver of new infections. Shedding of high viral titers from the respiratory tract, including shedding before the onset of symptoms, might have led to droplet and possibly aerosol transmission. Residents and staff members with undetected SARS-CoV-2 infection are likely to have contributed to transmission through interactions between and among residents and staff. The contribution of indirect contact transmission in this outbreak is not known. However, contaminated environmental surfaces and shared medical devices could also have played a role. Most of the early transmission appeared to have occurred in Unit 1, where the initial introduction of SARS-CoV-2 took place, several days before other units were involved. Early recognition of initial SARS-CoV-2 introduction combined with early interventions in all units might prevent spread within a facility.

The CDC and PHSKC confirmed Covid-19 infection in 26 symptomatic staff members associated with this skilled nursing facility as of March 26; these staff members most likely contributed to intrafacility transmission. A concurrent study of King County health care personnel with Covid-19 showed that 65% worked while symptomatic and that 17% of symptomatic health care personnel initially had mild, nonspecific symptoms and no fever, cough, shortness of breath, or sore throat.15 The potential for viral shedding from staff members with SARS-CoV-2 infection during either the presymptomatic or the mildly symptomatic phase of the illness reinforces current recommendations for expanded symptom screening for health care personnel and universal use of face masks for all health care staff in long-term care facilities.5

Current interventions for preventing SARS-CoV-2 transmission in health care settings rely primarily on the presence of signs and symptoms to identify and isolate residents and staff who might have Covid-19. The data presented here suggest that sole reliance on symptom-based strategies may not be effective to prevent introduction of SARS-CoV-2 and further transmission in skilled nursing facilities. Impaired immune responses associated with aging and the high prevalence of underlying conditions, such as cognitive impairment and chronic cough, make it difficult to recognize early signs and symptoms of respiratory viral infections in this population.16 Studies have shown that in the elderly, including those living in skilled nursing facilities, influenza often manifests with few or atypical symptoms, delaying diagnosis and contributing to transmission.17,18 Furthermore, symptom-based cohorting strategies could inadvertently increase the risk of SARS-CoV-2 exposure for uninfected residents, given that typical symptoms were common in those who tested negative.

Our investigation demonstrated a poor correlation between symptom onset and viral shedding that was potentially due to the difficulty of ascertaining precise dates of symptom onset or to differences in viral shedding in this population. Studies in other populations show that SARS-CoV-2 shedding is highest early in the illness.19,20 Our investigation shows that some facility residents shed virus for more than 7 days after symptom onset, a finding seen in some other populations.21 These data support current recommendations preferring a test-based strategy to discontinue transmission-based precautions for residents of skilled nursing facilities.22 If a non–test-based strategy is used, these data support extending the duration of transmission-based precautions.22

Because asymptomatic or presymptomatic residents might play an important role in transmission in this high-risk population, additional prevention measures merit consideration, including using testing to guide the use of transmission-based precautions, isolation, and cohorting strategies. The ability to test large numbers of residents and staff with rapid turn-around times may expedite cohorting of residents and staff in locations designated for the care of those with SARS-CoV-2 infection either in different locations within individual facilities or in separate facilities.

This investigation has several limitations. First, challenges in symptom ascertainment may have resulted in misclassification of symptom grouping for some residents. However, multiple sources of symptom data were used to minimize such misclassification. The accuracy of symptom ascertainment for this investigation is likely to be equivalent to, if not exceed, symptom screening in most skilled nursing facilities, and thus, these findings should be generalizable to this setting. Second, because this analysis was conducted among residents of a skilled nursing facility, it is not known whether the findings apply to the general population, including younger persons, those without underlying medical conditions, or similarly aged populations in the general community or in other long-term care settings. Third, asymptomatic staff members were not tested; therefore, we are unable to document their role in transmission in this facility.

SARS-CoV-2 can spread rapidly after introduction into skilled nursing facilities, resulting in substantial morbidity and mortality and increasing the burden on regional health care systems. Unrecognized asymptomatic and presymptomatic infections most likely contribute to transmission in these settings. During the current Covid-19 pandemic, skilled nursing facilities and all long-term care facilities should take proactive steps to prevent introduction of SARS-CoV-2. These steps include restricting visitors and nonessential personnel from entering the building, requiring universal use of face masks by all staff for source control while in the facility, and implementing strict screening of staff. Our data suggest that symptom-based strategies for identifying residents with SARS-CoV-2 are insufficient for preventing transmission in skilled nursing facilities. 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.5 Consideration should be given to test-based strategies for identifying residents and staff with SARS-CoV-2 infection for the purpose of excluding infected staff and cohorting residents, either in designated units within a facility or in a separate facility designated for residents with Covid-19.