From positive to negative: a time to event analysis during the first {COVID} 19 epidemic period

Background: The ability to identify the positive subjects is crucial for public health practice to reduce transmission and supporting contact tracing and isolation. The reliability of the criteria of the test-based criteria as the required condition for the reintroduction of the asymptomatic and positive patients of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the community was evaluated assessing the time span from positive to negative for RNA detection by Real Time – Polymerase Chain Reaction (RT-PCR). Methods. We used information concerning negative conversion time and the respective times. Cumulative probabilities of negative conversion time during the follow-up were evaluated by Crude Cumulative Incidences (CCIs). Non-parametric estimates of CCIs and respective 95% C.I.s were obtained. Results. We report the results for 52,186 individuals. 33486 subjects resulted negative or potentially negative with a CCI of 75.2% at 70 days from the rst swab (95% CI: 74.8% to 75.7%). 11,000 subjects deceased before 14/05/2020 without diagnosis of negative status (CCI 21.9%; 95% CI: 21.5% to 22.3%), at 56 days from the rst swab (maximum observed time to death). Conclusions. SARS-CoV-2 positivity is a condition that frequently lasts more than 30 days. More solid studies are required to determinate the signicance of a prolonged state of positivity and the consequences on the policies of dismission of quarantine and isolation.