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%), is 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.