Are saliva and deep throat sputum as reliable as common respiratory specimens for SARS-CoV-2 detection? A systematic review and meta-analysis

Objective The COVID-19 pandemic raises an urgent need for large-scale control through easier, cheaper, and safer diagnostic specimens, including saliva and sputum. We aimed to conduct a systemic review and meta-analysis on the reliability and sensitivity of SARS-CoV-2 detection in saliva and deep throat sputum (DTS) compared to nasopharyngeal, combined naso/oropharyngeal, and oropharyngeal swabs. Methods This systematic review and meta-analysis was performed according to the PRISMA statement. The inclusion criteria were studies that specifically assessed a sample of saliva or deep throat sputum (DTS) with at least one other respiratory specimen in patients with COVID-19 infection, based on RT-PCR tests. The DerSimonian-Laird bivariate random-effects model analysis performed using STATA software with the "metaprop" package. Results From 1598 studies, we retrieved 33 records, of which 26 studies were included for quantitative analysis. We found an overall sensitivity of 97%(95%CI,86-100) for bronchoalveolar lavage fluid, 92%(95%CI,80-99) for double naso/oropharyngeal swabs, 87%(95%CI,77-95) for nasopharyngeal swabs, 83% (95% CI 77-89) for saliva, 82% (95%CI,76-88) for DTS, and 44% (95%CI,35-52) for oropharyngeal swabs among symptomatic patients, respectively. Regardless of the type of specimens, the viral load and sensitivity in the severe patients were higher than mild and in the symptomatic patients higher than asymptomatic cases. Conclusion The present review provides evidence for the diagnostic value of different respiratory specimens and supports saliva and DTS as promising diagnostic tools for first-line screening of SARS-CoV-2 infection. However, sampling, storing, and laboratory assay needs to be optimized and validated before introducing a definite diagnosis tool. Saliva, DTS, nasopharyngeal, and even double naso/oropharyngeal swabs showed approximately similar results, and sensitivity was directly related to the disease severity. This review revealed a relationship between viral load, disease severity, and test sensitivity. None of the specimens showed appropriate diagnostic sensitivity for asymptomatic patients.
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