Daily mouthwash use does not prevent oropharyngeal gonorrhoea

Daily use of a mouthwash which has demonstrated inhibition of Neisseria gonorrhoeae (N. gonorrhoeae) growth in vitro did not reduce the risk of oropharyngeal gonorrhoea in men who have sex with men (MSM), according to results of the OMEGA* study from Australia.

“Our findings … indicate that daily use of mouthwash is unlikely to reduce or prevent the acquisition of oropharyngeal gonorrhoea,” noted the authors.

Participants in this multicentre, double-blind trial were 530 MSM aged ≥25 years with oropharyngeal gonorrhoea as diagnosed by nucleic acid amplification test (NAAT) or aged 16–24 years with a positive or negative test in the past 30 days. About 70 percent had oropharyngeal gonorrhoea in the preceding 30 days. They were randomized 1:1 to receive Listerine (intervention; n=266, median age 26 years) or Biotène (control; n=264, median age 25 years), with instructions to rinse and gargle with 20 mL of mouthwash for 60 seconds at least once daily for 12 weeks. Oropharyngeal and saliva samples were obtained at week 6 and 12 visits, and saliva samples were mailed at weeks 3 and 9.

A total of 219 and 227 individuals in the intervention and control groups, respectively, were included in the primary analysis.

The proportion of MSM diagnosed with oropharyngeal N. gonorrhoeae infection (NAAT-confirmed positive result from oropharyngeal or saliva swab) at any point over 12 weeks did not differ between those assigned to the intervention or control (7 percent vs 4 percent; adjusted risk difference [adjRD], 2.5 percent, 95 percent confidence interval [CI], -1.8 to 6.8). [Lancet Infect Dis 2021;21:647-656]

Among those with detected N. gonorrhoeae, the gonococcal load did not differ between groups.

Cumulative incidence of oropharyngeal gonorrhoea at the week 12 visit also did not differ between the intervention and control groups (7 percent vs 4 percent; adjRD, 3.1 percent, 95 percent CI, -1.4 to 7.7).

Difficulty using the recommended mouthwash dose was experienced by more participants in the intervention than control group (61 percent vs 26 percent; p<0.0001).

Overall, self-reported mouthwash adherence was high (85 percent with ≥80 percent use), with comparable adherence levels in the intervention and control groups (86 percent vs 83 percent). While 59 percent of participants reported using the recommended amount of mouthwash, the proportion was lower with the intervention vs control (46 percent vs 70 percent; p<0.0001). Similarly, of the 45 percent who adhered to the recommended 60 seconds of use, the proportion was lower among participants in the intervention vs control group (39 percent vs 52 percent; p=0.0015).

Anorectal gonorrhoea was detected in 7 and 4 percent of the intervention and control groups, respectively (adjRD, 2.5 percent) and urethral gonorrhoea in <1 and 4 percent, respectively (adjRD, -4.3 percent). Overall, gonorrhoea was diagnosed in 12 and 9 percent, respectively (adjRD, 2.6 percent).

Chlamydia, syphilis, and HIV incidence also did not differ between groups.

“[A]ntimicrobial resistance in N. gonorrhoeae has emerged as an urgent threat to public health,” the authors said. The rising incidence of gonorrhoea infections is likely to further increase the incidence of antimicrobial resistance, highlighting the need for new prevention strategies.

While this study showed that mouthwash had no effect on oropharyngeal gonorrhoea incidence, “previous research suggests that mouthwash might reduce the infectivity of oropharyngeal gonorrhoea,” they added. “[F]urther studies of mouthwash examining its inhibitory effect on N. gonorrhoeae are warranted to determine if it has a potential role for the prevention of transmission,” they said.

The authors postulated that a different method of mouthwash administration may have produced different results, which is also a potential avenue for research. Timing of mouthwash use was also not specified to the participants; as such, using mouthwash close to time of exposure could have resulted in a different outcome.