Sars-CoV-2 PCR persistence and review of population swabbing in QLD's first wave

Abstract

Introduction: A cornerstone of the public health response to Sars-CoV-2 has been isolation of positive patients. Initially, criteria for release from isolation required two negative swabs in addition to symptom criteria; however, this phased out by June 4 as viral RNA can persist as {\textquoteleft}viral litter{\textquoteright} with little implication on infectivity.¹,² The large collection of repeat tests prior to June 4 enabled a review of local demographic characteristics for swabbed individuals and duration of RNA persistence. Methods: We conducted an exploratory analysis of Queensland's (QLD) pathology SARS-CoV-2 reverse transcriptase polymerase chain reaction (RT-PCR) test results. Kaplan Meier analysis was used to estimate time to viral clearance and Cox regression to explore effects of age and sex. Results: We analysed 97 476 individuals{\textquoteright} results between January 19 and June 4 2020. Median age was 41y (range <1-105y), 57.2% (95% CI 57.2, 57.2) were female, and 958 individuals (0.98%; 95% CI 0.92,1.05) tested positive for SARS-CoV-2. Positivity rates were lower in regional areas than cities, in females (OR 0.80, 95% CI 0.70, 0.91), and in those aged 16y and below (p<0.01, test for trend).Of the 958 positive individuals, 243 had two or more (max 17) additional tests, and 92% (95% CI 88.1, 95.2) remained positive after 10 days (max 76 days) after the initial result. Median time to apparent viral clearance was longer in those 65y and over compared to those under 65y (29 v 43 days, HR 1.85; 95% CI 1.17, 2.90), and was unaffected by sex (HR 0.93; 95% CI 0.66, 1.30).Conclusion: Detectable RNA can persist for long periods of time, particularly in the elderly. REF:1. Wolfel R, et al. Virological assessment of hospitalized patients with COVID-2019. Nature. 2020;581(7809):465-9.2. Why some Covid-19 patients might have tested positive twice. Quartz April 16 2020. https://qz.com/1837798/why-some-covid-19-patients-might-have-tested-positive-twice/