Antigenic rapid test for SARS-CoV2 screening of individuals newly admitted to detention facilities: sensibility in an asymptomatic cohort

BACKGROUND: Since the start of the Sars-CoV-2 pandemic, attention was called on the potential risk of COVID-19 outbreaks occurring inside prisons. In detention facilities, timely and accurate diagnosis is essential for allowing case isolation and contact tracing to avoid the spread of the infection. Until recently, reverse-transcriptase polymerase chain reaction (rt-PCR) was the recommended method to diagnose SARS-CoV-2 infection. However, antigen-detecting rapid diagnostic tests (ag-RDT) have emerged as point-of-care testing techniques. OBJECTIVES: Here, we evaluate the use of ag-RDT for screening of individuals newly admitted to San Vittore prison (SV), a pre-trial prison, in Milan (Lombardy region, Italy), during the second SARS-CoV2 epidemic peak. METHODS: During the period 1 October-31 December 2020, ag-RDT and rt-PCR were performed individuals newly admitted to SV. RESULTS: Among 504 detained individuals tested, 21 (4,2%) resulted positive to rt-PCR. Of these, 10 had tested negative with ag-RDT and 11 had concordant results. Rt-PCR cycle threshold (CT) values were above 35 for the individuals with ag-RDT negative test, therefore the cases missed by the ag-RDT are unlikely to transmit disease. For all the individuals with ag-RDT positive results, CT values were below or equal to 27. In our study population, ag-RDT sensitivity was 52.4% (29.8%-74.3%), positive predictive value (PPV) was 100% and negative predictive value was 98.0% (96.8%-98.7%). DISCUSSION: Our study showed that ag-RDT is a promising and useful component of serial testing strategies in prison settings to perform SARS-CoV2 screening at admission based to its high PPV, ease of use, lower costs and resource needs.