Survival analysis of time to SARS-CoV-2 PCR negativisation to optimise PCR prescription in health workers: the Henares COVID-19 healthcare workers cohort study.

OBJECTIVES: Reverse transcriptase PCR (RT-PCR) is considered the gold standard in diagnosing COVID-19. Infected healthcare workers do not go back to work until RT-PCR has demonstrated that the virus is no longer present in the upper respiratory tract. The aim of this study is to determine the most efficient time to perform RT-PCR prior to healthcare workers' reincorporation. MATERIALS AND METHODS: This is a cohort study of healthcare workers with RT-PCR-confirmed COVID-19. Data were collected using the medical charts of healthcare workers and completed with a telephone interview. Kaplan-Meier curves were used to determine the influence of several variables on the time to RT-PCR negativisation. The impact of the variables on survival was assessed using the Breslow test. A Cox regression model was developed including the associated variables. RESULTS: 159 subjects with a positive RT-PCR out of 374 workers with suspected COVID-19 were included. The median time to negativisation was 25 days from symptom onset (IQR 20-35 days). Presence of IgG, dyspnoea, cough and throat pain were associated with significant longer time to negativisation. Cox logistic regression was used to adjust for confounding variables. Only dyspnoea and cough remained in the model as significant determinants of prolonged negativisation time. Adjusted HRs were 0.68 (0.48-096) for dyspnoea and 0.61 (0.42-0.88) for dry cough. CONCLUSIONS: RT-PCR during the first 3 weeks leads to a high percentage of positive results. In the presence of respiratory symptoms, negativisation took nearly 1 week more. Those who developed antibodies needed longer time to negativisate.