White EM, Santostefano CM, Feifer RA, Kosar CM, Blackman C, Gravenstein S, Mor V.
Introduction
Asymptomatic transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may be a major contributing factor in skilled nursing facility (SNF) outbreaks. However, limited knowledge exists regarding the prevalence of asymptomatic and presymptomatic infection in this setting. Although an estimated 40% to 45% of SARS-CoV-2 infections in the general population are asymptomatic at time of testing,1 a small number of US and international reports have documented higher asymptomatic rates in SNFs.2-5 We examined asymptomatic and presymptomatic infection rates in a large multistate sample of US SNFs, and examined variation in case counts by SARS-CoV-2 prevalence in the counties where SNFs are located.
Methods
We used data from Genesis HealthCare, a multistate long-term care provider with roughly 350 SNFs. By combining electronic medical record data with daily infection logs that recorded testing dates and results, we identified all unique resident cases of SARS-CoV-2 confirmed by polymerase chain reaction testing between March 16, 2020, and July 15, 2020. This study was approved by the Brown University institutional review board, which waived the requirement for participant informed consent because all data were deidentified.
All residents underwent nursing assessments at least twice daily. We classified residents as having new SARS-CoV-2–related symptoms if nurses documented in a structured change in condition note any of the symptoms listed in the eMethods in the Supplement. Residents were classified as symptomatic at presentation if they had new symptoms within 5 days before their first positive test date, presymptomatic if they had no symptoms in the 5 days before testing but developed symptoms within 14 days thereafter, and asymptomatic if they had no symptoms from 5 days pretest to 14 days posttest.
Test availability varied regionally and temporally. We analyzed cumulative case counts for SNFs that underwent 1 or more point-prevalence surveys, either facility-wide (all residents tested) or unit-based (all residents on specific units tested without testing the whole house). The cumulative case count includes cases detected during surveys plus those detected during symptom- or exposure-driven testing at any time from March 16, 2020, to July 15, 2020. We report the percentage of cumulative cases who were asymptomatic, presymptomatic, and symptomatic at presentation.
In addition, we describe variation in counts of combined asymptomatic and presymptomatic cases at time of initial survey for SNFs that underwent facility-wide testing, across counties located in the top 5%, middle 20%, and bottom 75% of US counties for SARS-CoV-2 prevalence. County data were obtained from the Johns Hopkins University Coronavirus Resource Center (https://coronavirus.jhu.edu).
Results
As of July 15, 2020, 182 SNFs in 20 states had at least 1 SARS-CoV-2 case and underwent some form of a point prevalence survey, with a cumulative total of 5403 unique resident cases (Table). Overall, 2194 (40.6%) cases were asymptomatic, 1033 (19.1%) were presymptomatic, and 2176 (40.3%) were symptomatic at presentation. The SNFs that underwent at least 1 facility-wide survey (N = 173) identified slightly higher cumulative rates of asymptomatic and presymptomatic infection than SNFs limited to unit-based surveys (N = 9) (P = .02). Of the 5011 cases identified in SNFs with facility-wide testing, 2049 (40.9%) were asymptomatic, 969 (19.3%) were presymptomatic, and 1993 (39.8%) were symptomatic at presentation. Of the 392 cases identified in SNFs with unit-based testing 145 (37.0%) were asymptomatic, 64 (16.3%) were presymptomatic, and 183 (46.7%) were symptomatic at presentation.
Among the 173 SNFs that underwent facility-wide surveys, those in counties with higher SARS-CoV-2 prevalence generally had higher combined counts of asymptomatic and presymptomatic cases at their initial survey than SNFs in counties with lower prevalence (Figure).
Discussion
We observed high asymptomatic and presymptomatic SARS-CoV-2 infection rates in a large multistate sample of SNFs, demonstrating the importance of universal testing for identifying and isolating cases. The SNFs located in areas with high SARS-CoV-2 prevalence detected higher numbers of asymptomatic and presymptomatic cases during initial point prevalence surveys, building on emerging evidence that SNF location is an important predictor of outbreaks.6