Can gargling with mouthwash stop coronavirus from its tracks?

Rinsing with mouthwash that contains povidone-iodine (PI) or cetylpyridinium chloride (CPC) helps reduce SARS-CoV-2 levels in the saliva of COVID-19 patients, with the effect persisting for up to 6 hours, as shown in a study from Singapore.

“These mouth-rinses could be a useful preprocedural transmission reduction strategy in clinical dental settings, where aerosol generation is unavoidable,” said lead researcher Dr Chaminda Jayampath Seneviratne from the National Dental Research Institute Singapore (NDRIS).

“Also in asymptomatic COVID-19 patients, the routine use of antiseptic mouth-rinsing could be a cost-effective approach in reducing viral outspread, with potentially low health risk,” he added.

To test whether a commercial oral rinse would reduce salivary SARS-CoV-2 load, Seneviratne and colleagues randomized 16 infected patients to rinse their mouth with one of the following: 5 ml of PI mouthwash diluted with 5 ml of water (n=4), 15 ml of undiluted chlorhexidine gluconate (CHX) mouthwash (n=6), 20 ml of 0.075% CPC (n=4), or 15 ml sterile water (n=2; control) for 30 seconds. The team collected saliva samples at baseline and after using an oral rinse (5 minutes, 3 hours, and 6 hours).

Results of the RT-PCR analysis showed that the concentration of SARS-CoV-2 in the saliva samples was similar across the 5-minute, 3-hour, and 6-hour time points within each of the four groups. However, compared with the water control, the CPC group showed a markedly lower salivary viral load at the 5-minute and 6-hour mark (p<0.05). [Infection 2020;doi:10.1007/s15010-020-01563-9]

Likewise, the PI group had lower viral load than the water control at all the time points examined, but the difference was only meaningful at 6 hours (p<0.01).

The effect of CHX on viral load in the saliva at 5 minutes after rinsing was varied, but the trends at the 3-hour and 6-hour time points were consistent with other mouthwashes.

Salivary SARS-CoV-2 levels were determined using cycle threshold (Ct) values on RT-PCR. Ct was inversely correlated with viral load and could therefore serve as an indirect method of arbitrarily quantifying the viral load in the current sample, Seneviratne noted.

“This [study] is to our knowledge the first randomized clinical study to examine the efficacy of commercial mouth-rinses on SARS-CoV-2 viral load in COVID-19 patients,” he said.

Seneviratne mentioned only a single clinical trial evaluating the effect of essential oil containing oral rinse on Herpes simplex virus. Rinsing led to detection of effectively zero recoverable virions at 30 seconds after use, and the reduction in salivary load was sustained significantly for 60 minutes, which was the last time point recorded. [J Clin Periodontol 2005;32:341-346]

“Hence, despite [the small sample size], the present study provides a novel insight into the quantity of SARS-CoV-2 in saliva, [as well as] the much-needed evidence on the efficacy of commercial [mouthwash] for salivary viral load reduction in a group of COVID-19 patients in Singapore,” he said.

CPC is a quaternary ammonium compound that exerts its antiviral effect through disruption of the viral lipid envelope through physicochemical interactions. On the other hand, PI has been reported to have an antiviral activity against both enveloped and nonenveloped viruses. [Dermatology 1997;195:29-35; Nat Microbiol 2020;5:536-544] 

Given that CPC and PI are able to destroy the lipid membrane of the SARS-CoV-2, Seneviratne is positive that oral rinses represent a safe, effective strategy to reduce the viral transmission through oral route. “This holds potential as a strategy with high public health impact considering that mouthwash is available over the counter.”

However, he stressed that despite the encouraging findings, the study still advocates the use of surgical masks as a control measure.

“In addition, during any aerosol-generating procedures in dental clinic, it is necessary to don appropriate personal protection equipment, use four-handed dentistry, high evacuation suction, and dental dams to minimize droplet spatter and aerosols,” Seneviratne said.