High incidence of COVID-19 at nursing homes in Madrid, Spain, despite preventive measures

despite the strict restrictions adopted during the lockdown, demonstrates the ability of SARS-CoV-2 to cause outbreaks. Objective. To assess the impact of COVID-19 at nine nursing homes in Madrid, Spain, during the first wave of COVID-19 infection and lockdown period when preventive measures were taken to avoid transmission among residents. Methods. Nine hundred forty-two residents and 846 staff members from nine nursing homes participated in the study (April 18 to June 20, 2020). All participants were tested for SARS-CoV-2 in the nasopharynx by PCR and for IgG antibodies detection. Microbiological status at sampling was defined as active infection (positive PCR +/- presence of antibodies), past infection (negative PCR + presence of antibodies), or naive participants (negative PCR + absence of antibodies). Results. Laboratory results helped classify the residents as having active infection (n=224; 23.8%), past infection (n=462; 49.1%), or being naive (n=256; 27.1%); staff members were actively infected (n=127; 15.1%), had had a past infection (n=290; 34.2%), or were naive (n=429; 50.7%). Overall, the percentage of participants with COVID-19 was significantly higher in residents than in staff members (72.8% vs 49.2%; P=0.001). The clinical situation of residents vs staff at sampling was as follows: acute manifestations compatible with COVID-19 (7.3% vs 3.9%; P<0.01) and no manifestations of infection (92.7% vs 96.0%; P<0.01). A large proportion of both asymptomatic and symptomatic residents (69.4% vs 86.6%; P=0.015) had positive PCR results (mostly alongside positive IgG determinations). Conclusions. COVID-19 affects 75% of the residents in nursing homes in Madrid. The high impact in these settings,