The role of mouthwash sampling in SARS-CoV-2 diagnosis

Abstract

Background: The current practice of COVID-19 diagnosis worldwide is the use of oro-nasopharyngeal (ONP) swabs. Our study aim was to explore mouthwash (MW) as an alternative diagnostic method, in light of the disadvantages of ONP swabs.

Methods: COVID-19 outpatients molecular-confirmed by ONP swab were repeatedly examined with ONP swab and MW with normal saline (0.9%). Other types of fluids were compared to normal saline. The Cq values obtained with each method were compared.

Results: Among 137 pairs of ONP swabs and MW samples, 84.6% (116/137) of ONP swabs were positive by at least one of the genes (N, E, R). However MW detected 70.8% (97/137) of samples as positive, which means 83.6% (97/116) out of positive ONP swabs, missing mainly Cq value > 30. In both methods, the N gene was the most sensitive one. Therefore, MW samples targeting N gene, which was positive in 95/137 (69.3%), are comparable to ONP swabs targeting E and R genes which gave equal results-95/137 (69.3%) and 90/137 (65.7%), respectively. Comparing saline MW to distilled water gave equal results, while commercial mouth-rinsing solutions were less sensitive.

Conclusions: MW with normal saline, especially when tested by N gene, can effectively detect COVID-19 patients. Furthermore, this method was not inferior when compared to R and E genes of ONP swabs, which are common targets in many laboratories around the world.

Keywords: COVID-19; Gargling; Mouth rinse; Saliva; Throat-wash.

Fig. 1

Number of positive results of oro-nasopharyngeal swab (N = 137 tests) in each target (N, E, R genes) and their overlapping

Fig. 2

Number of positive results of saline mouthwash (N = 137 tests) in each target (N, E, R genes) and their overlapping

Fig. 3

MW as tested by the N target in comparison to ONP swabs tested by N, E, and R targets (n = 137). N gene ONP swab, positive samples of ONP swabs tested by N target; E gene ONP swab, positive samples of ONP swabs tested by E target; R gene ONP swab, positive samples of ONP swabs tested by R target; N gene MW, positive samples of MW tested by N target

Fig. 4

The performance of different mouth-fluid washes in comparison to positive samples by ONP swabs as tested by N target. N-ONP, positive samples of ONP swabs tested by N target; ONP-3 pos genes, ONP swabs positive in all 3 gene targets (N,E,R); N saline, positive samples of saline MW tested by N target; N water, positive samples of water MW tested by N target; N Orbitol, positive samples of Orbitol MW tested by N target; N Listerine, positive samples of Listerine MW tested by N target. *137 samples were tested; among them, 114 were positive in ONP tested by N target (= 100%). **59 samples were tested; among them, 48 were positive in ONP tested by N target (= 100%). ***16 samples of Orbitol were tested; among them, 12 were positive in ONP tested by N target (= 100%). Twelve samples of Listerine were tested; among them, 12 were positive in ONP tested by N target (= 100%)