Comparison of Saliva and Mid-Turbinate Swabs for Detection of COVID-19

ABSTRACT

BackgroundSaliva is an attractive sample for detecting SARS-CoV-2. However, contradictory reports exist concerning the sensitivity of saliva versus nasal swabs. MethodsWe followed close contacts of COVID-19 cases for up to 14 days from last exposure and collected self-reported symptoms, mid-turbinate swabs (MTS), and saliva every two or three days. Ct values, viral load, and frequency of viral detection by MTS and saliva were compared. Results58 contacts provided 200 saliva-MTS pairs; 14 contacts (13 with symptoms) had one or more positive samples. Saliva and MTS had similar rates of viral detection (p=0.78) and substantial agreement ({kappa}=0.83). However, sensitivity varied significantly with time since symptom onset. Early on (days -3 to 2), saliva had 12 times (95%CI 1.2, 130) greater likelihood of viral detection and 3.2 times (95% CI 2.8, 3.8) higher RNA copy numbers compared to MTS. After day 2 post-symptoms, there was a non-significant trend toward greater sensitivity using MTS. ConclusionSaliva and MTS demonstrated high agreement making saliva a suitable alternative to MTS for COVID-19 detection. Saliva was more sensitive early in the infection when transmission is most likely to occur, suggesting that it may be a superior and cost-effective screening tool for COVID-19.