COVID-19 in nursing homes: What syndromic and virological surveillance revealed about the first two epidemic waves.

BACKGROUND: Nursing homes were affected by COVID-19, and limited testing capacity during the first wave highlighted the value of complementary surveillance approaches. OBJECTIVE: To characterize clinical presentations, virological findings, and mortality identified through syndromic and virological surveillance during two COVID-19 waves. MATERIALS AND METHODS: A retrospective study was conducted in 16 nursing homes in Northeastern France, including 1,493 residents monitored from February 2020 to February 2021. Residents were classified into four clinical sign patterns: combined general and respiratory signs (G and R), R only, G only, and asymptomatic positive SARS-CoV-2 tests (T+ only). Outbreaks were defined by at least three residents presenting G and R or T+ only within four consecutive days. Wave 2 analyses were conducted separately before and during immunization. RESULTS: Outbreak frequency and duration remained high during both epidemic waves, although smaller facilities were less likely to experience outbreaks. The proportion of residents presenting G and R declined from 62.9% during wave 1 to 53.0% and 38.9% during the pre-immunization and immunization periods, respectively (p < 0.001), whereas G only presentations increased. Virological testing coverage among CSPs increased from 41.0% to 84.8% and 79.2%, respectively. Estimated 8-week mortality decreased from 25.4% to 20.5% and 12.8% (p = 0.002). In multivariable analysis, clinical sign patterns (highest risk among G and R), older age, male sex, and not being tested were independently associated with mortality, while epidemic period was not. DISCUSSION: These findings highlight the complementary value of syndromic and virological surveillance for characterizing COVID-19 outbreaks in nursing homes.