Could certain mouthwashes reduce transmissibility of COVID-19?

Data sources Six electronic databases were searched including PubMed/Medline, Embase, Web of Science, Scopus, Cochrane, and Latin American and Caribbean Literature in Health Science (LILACS). Grey literature was also examined. There were no restrictions with regards to language, time of publication or participant demographics including gender, age and ethnicity.Study selection Both clinical and in vitro studies were included in the data search. Inclusion and exclusion criteria were clearly identified. Study selection was carried out in two phases by two independent reviewers. The studies included fitted the following criteria: studies that hypothesised the use of mouthwashes as a form of intervention to decrease the viral load in saliva contaminated with coronavirus. Two other studies were included in this review and both were conducted in Germany, performed in vitro, which tested povidone-iodine (PVP-I) mouthwash at two different concentrations: 1% and 7%. Both studies used the same culture mediums for clean and dirty conditions, and the evaluated outcome was the viral titre of MERS-CoV and SARS-CoV. The studies were published in 2015 and 2018. Neither study evaluated the action of this mouthwash on SARS-CoV-2 infection.Data extraction and synthesis The extraction of data followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline process. Studies chosen for analysis included assessment of the following data parameters for risk of bias: cell origin and cell type used, duration of exposure, frequency of exposure, magnetic flux density of exposure, environmental background magnetic field, use of control treatment, temperature control, blinding of exposure, randomisation of exposure, measurement of cell vitality, identical methods for control and exposure groups, randomisation of data measurements and potential industry sponsorship.Results One study assessed the effect of the mouthwash on MERS-CoV and the other on both MERS-CoV and SARS-CoV. In both studies, following 15 seconds of exposure to the mouthwash, a reduction in viral load of >99.99% was seen. There was a measurable reduction in viral titre in the samples, with one study reporting a reduction to 4.30 log10 TCID50/ml from 6.00-6.50 log10 TCID50/ml. Other mouthwashes such as hydrogen peroxide and chlorhexidine were not assessed in these studies.Conclusions The study concludes that PVP-I mouthwash at concentrations of 1% and 7% for 15 seconds may be effective at reducing the viral load of COVID-19 in human saliva. The level of scientific evidence, however, is low.