Rinsing a Pandemic Down: Effects of Oral Hygiene in SARS-CoV-2: A Two-Center Prospective Pilot Study

Background: Saliva sampling is increasingly used for respiratory virus diagnostics in dentistry and oral medicine due to patient comfort and reduced exposure risk. How routine behaviors-mechanical oral hygiene, rinsing, and food intake-affect short-term SARS-CoV-2 detectability remains insufficiently characterized for clinical workflows. Methods: In this international two-center pilot study, twelve RT-PCR-confirmed COVID-19 patients provided paired mouth-rinse saliva samples and pharyngeal swabs at predefined time points. The study assessed (I) an intensified 3 min mechanical oral hygiene protocol (toothbrushing of teeth, gingiva, tongue, and palate, followed by toothpaste-saliva gargling); (II) repeated short mouth rinses; and (III) postprandial sampling. Viral RNA was quantified by RT-PCR; Ct-trajectories were analyzed intra-individually. Results: Cycle threshold (Ct) values from pharyngeal swabs remained relatively stable over time, whereas mouth-rinse samples exhibited notable fluctuations throughout the 24 h period. An average increase of 3 Ct units was observed three minutes after the final mouth rinse (T24+3). Meal ingestion was associated with increased Ct values, rising by 4-5 units for pharyngeal swabs and 3-11 units for mouth rinses immediately after eating. Conclusions: In clinical dental settings, saliva diagnostics are feasible but acutely modulated by common behaviors. Mechanical oral hygiene, brief rinsing, and food intake can transiently reduce detectable oral SARS-CoV-2 RNA, with potential implications for timing of sampling, chairside triage, and infection-control protocols. This pilot study provides initial evidence supporting the development of standardized pre-analytical instructions (e.g., fasting window, pre-rinse policy, and sampling timing relative to oral hygiene and meals) to enhance the reliability of saliva-based testing in dental care.