Seroprevalence of SARS-CoV-2 Among Skilled Nursing Facility Residents and Staff Members — Los Angeles County, August–September 2020

Malenfant, Jason H; Eslami, Michelle; Dao, Bonnie L; Moore, Leo; Green, Nicole; Silver, David; OYong, Kelsey; Ruparelia, Ashutosh; Fisher, Rebecca; Wood, Julia S; Faisal, Mohammad; Washburn, Faith; Shvartsblat, Steve; Jewell, Mirna P; Romo, Tiffany; Foo, Chelsea; Salazar, Angela; Rajagopalan, Shobita; Rubin, Zachary A; Gounder, Prabhu

BACKGROUND: The prevalence of current/past coronavirus disease 2019 (COVID-19) in skilled nursing facility (SNF) residents is unknown because of asymptomatic infection and constrained testing capacity early in the pandemic. We conducted a seroprevalence survey (SPS) to determine a more comprehensive prevalence of past COVID-19 in Los Angeles County SNF residents and staff members. METHODS: We recruited participants from 24 facilities; participants were requested to submit a nasopharyngeal (NP) swab for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) PCR testing and serum for detection of SARS-CoV-2 antibodies. All participants were cross-referenced with our surveillance database to identify persons with prior positive SARS-CoV-2 results. RESULTS: From August 18 to September 24, 2020, we enrolled 3,305 participants (1,340 residents and 1,965 staff members). Among 856 residents providing serum, 362 (42%) had current/past SARS-CoV-2 infection. Of the 346 serology positive residents, 199 (58%) did not have a documented prior positive SARS-CoV-2 PCR result. Among 1,806 staff members providing serum, 454 (25%) had current/past SARS-CoV-2 infection. Of the 447 serology positive staff members, 353 (79%) did not have a documented prior positive SARS-CoV-2 PCR result. CONCLUSIONS: Past testing practices and policies missed a substantial number of SARS-CoV-2 infections in SNF residents and staff members.