Large-scale silane bead-based SARS-CoV-2 testing of a nursing home in Spain identifies a viral reservoir during lockdown period

Background: Spain is one of the countries most heavily affected by the COVID-19 pandemic. As in other countries such as UK and USA, nursing homes have been an important human reservoir for the virus and the population with the highest mortality worldwide. The presence of asymptomatic carriers within nursing homes is one of the factors that could provoke new outbreaks during the relaxing of lockdown measures. Methods: We developed a high-throughput protocol for RNA extraction of patient samples based on silane magnetic beads in multi-well plates. The sensitivity, specificity and reproducibility rates were assessed using positive and negative clinical samples from the Clinica Universidad de Navarra, Spain. We utilized the protocol to test a pilot cohort of 138 residents and 87 staff from a nursing home in Northern Navarre, Spain. Findings: Our protocol showed high sensitivity (100%), specificity (96.0%) and linear correlation with PCR cycle threshold values obtained with a standard testing kit (R2 = 0.807, p=3E-05). Testing of 225 individuals from the nursing home revealed 63 residents (46%) and 14 staff (16%) positive for SARS-CoV-2. Only 18 of the positive residents (28.6%) were symptomatic at time of testing. During follow-up, six PCR-negative symptomatic residents were retested and resulted positive. One-month mortality among positive residents was higher than in negative residents (15.9% vs 1.3%), regardless of age or comorbidities. Interpretation: Rapid silane bead-based RNA extraction expanded the testing capabilities and COVID-19 patients were promptly identified. Personal and public health measures were enacted to avoid spreading and tighten clinical surveillance. The ability to easily adapt the technical capabilities of academic research centers to large-scale testing for SARS-CoV-2 could provide an invaluable tool for ensuring a safe lifting of lockdown in countries with high numbers of cases.