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

Background Saliva is an attractive sample for detecting SARS-CoV-2. However, contradictory reports exist concerning the sensitivity of saliva versus nasal swabs. Methods We 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. Results 58 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 (κ=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. Conclusion Saliva 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.