Early and consecutive RT-PCR tests with both oropharyngeal swabs and sputum could improve testing yield for patients with COVID-19: An Observation Cohort Study in China

Song, Yangzi; Chen, Chen; Wang, Yu; Zhang, Ju; Chen, Meiling; Gao, Guiju; Wang, Sa; Yang, Di; Song, Rui; Wang, Linghang; Xie, Wen; Yu, Fengting; Yan, Liting; Wang, Yajie; Zeng, Hui; Zhang, Fujie

OBJECTIVE: The real-time polymerase chain reaction (RT-PCR) test is recommended for diagnosis of COVID-19 and provides a powerful tool to identify new infections and contact tracing. In fact, as COVID-19 prevalence decreases, this remains the main preventive measure to avoid rebound. However, inconsistent results due to biological sample variability in collection timing post infection and sampling procedures, misleads our application in clinic. METHODS: We applied Kaplan-Meier method and multivariate Logistic regression on the RT-PCR results from 258 confirmed patients with COVID-19 to evaluate the factors associated with negative conversion. We also estimated the negative percentages among patients who had tested twice or more and compared the proportions by oropharyngeal swab, sputum and combined double testing, respectively. MAIN RESULTS: The proportion of negative conversion was 6.7% at the 4(th) day, 16.4% at the 7(th) day, 41.0% at two weeks and 61.0% at three-weeks post-admission. We also found 34.1% and 60.3% with at least one negative RT-PCR result at the 7(th) days and 14(th) days after symptom onset, respectively. The negative proportion in sputum was higher than that in oropharyngeal swab in the early stage but lowered after symptoms. CONCLUSION: In the absence of effective treatments or vaccines, efficient testing strategies are critical to control COVID-19 epidemic. According to this study, early, consecutive and combined double testing will be the key to identify infected patients, particularly for asymptomatic and mild symptomatic cases, and minimize misdiagnosis and ineffective isolation of infected patients.