Clinical information and blood samples were available for 9,332 residents (mean age 86.7 ± 8.1 years, 76.4% women) and 10,614 staff (mean age 45.6 ± 11.5, 86.2% women). Up to 84.4% of residents had
frailty, 84.9% co-morbidity and 69.3%
cognitive impairment; 65.2% of workers were health-aides.COVID-19 seroprevalence was 55.4% (95% confidence interval (CI), 54.4-56.4) for older adults and 31.5% (30.6-32.4) for staff. In multivariable analysis,
frailty of residents was related with seropositivity (odds ratio (OR): 1.19, P = 0.02). In the case of staff, age > 50 years (2.10, P < 0.001),
obesity (1.19, P = 0.01), being a health-aide (1.94, P < 0.001), working in a center with high seroprevalence in residents (3.49, P < 0.001) and contact with external cases of
COVID-19 (1.52, P < 0.001) were factors associated with seropositivity. Past symptoms of
COVID-19 were good predictors of seropositivity for residents (5.41, P < 0.001) and staff (2.52, P < 0.001).
CONCLUSIONS: Level of dependency influences risk of
COVID-19 among residents. Individual and work factors, contacts outside the
nursing home are associated with
COVID-19 exposure in staff members. It is key to strengthen control measures to prevent the introduction of
COVID-19 into care facilities from the community.