Listerine for gonorrhoea under the microscope again

OMEGA study underway investigating the reduction of
transmission of gonorrhoea by using antiseptic mouthwash

by Anne Crawford

Early this year we reported that a study by Melbourne Sexual Health Centre (MSHC) researchers found that gargling with Listerine mouthwash could inhibit the growth of the bacteria responsible for pharyngeal gonorrhoea.

The study of gay and bisexual men, while preliminary, attracted global attention. It was widely reported in the media including in newspapers, on radio, online, YouTube and Twitter, and attracted what co-author Dr Eric Chow said was a "massive" amount of emails.


The study presented a potentially novel way to reduce gonorrhoea prevalence and transmission at a time when gonorrhoea rates are rising and the threat of bacterial resistance to existing treatments growing.

Neisseria gonorrhoeae is one of the most common sexually transmissible infections worldwide. It has increased substantially in Australia in recent years; from around 50 cases per 100,000 male population  between 2006 and 2009, rising to 117 cases in 2015, mostly in men who have sex with men (MSM).

Interest in the MSHC research is flaring again with the recent publication of three papers and a letter on the topic.

A larger study funded by the NHMRC to test the original results is now underway, the protocol of which was published in the journal 'BMC Infect Diseases'. The OMEGA (Oral Mouthwash to Eradicate GonorrhoeA) Study, a double-blind trial, is testing 510 MSM across five clinical sites in Sydney and Melbourne.

The study expands on the first trial which enlisted 196 gay/bisexual MSM who had previously tested positive for gonorrhoea in their throat, and who were asked to do a one-off rinsing with the over-the-counter mouthwash. The current trial spans three months with the larger sample size and is also testing different brands of commercially available mouthwash to see if they have a similar effect to Listerine.

Dr Chow, Senior Research Fellow at the MSHC and Central Clinical School, said the OMEGA study, led by him and centre director Professor Christopher Fairley, was progressing well with results expected to be out in 2018.

Another paper in ‘Sexually Transmitted Diseases’ elicited an editorial in the same edition.

The MSHC study, led by Associate Professor Lei Zhang, developed a unique mathematical model using data for anatomic site-specific prevalence of oropharyngeal, anal and urethral gonorrhea. It concludes that kissing potentially plays an important role in N. gonorrhoeae transmission among MSM, accounting for more than 70% of the disease in this group. It suggests that a mouthwash could substantially reduce prevalence of the disease in MSM.

The assertions are “bold”, the editorial writes. And while such mathematical models are vital, the study lacked empirical evidence it says, a limitation acknowledged by the authors.

“For science to advance, however, we must be open to new ideas and challenges to conventional wisdom,” it says, adding that it could be conceivable that oropharyngeal infections played a key role in sustaining gonorrhoea in MSM via kissing, and that a mouthwash with efficacy against it could have a “notable population-level impact on gonorrhea”.

“I think the response in the editorial was very good,” said Dr Chow. “They’re acknowledging too that there are a lot of unknowns – we’re trying to solve these puzzles.

“We won’t know until the end of the trial but the evidence to date suggests it will probably work,” he said.

“Gonorrhoea is a really serious problem because of antibiotic resistance – if that keeps building up we won’t have an antibiotic to treat it with.”

A third study on self-reporting the daily use of mouthwash among MSM showed that this use increased with age while pharyngeal gonorrhoea detection decreased with age, although the researchers did not know why younger men were less likely to use the mouthwash.

A letter by the researchers published in the September edition of ‘Sexually Transmitted Infections’ sought to correct a number of misconceptions about the use of the mouthwash that have arisen since the original study.

“I’ve no idea why people got this idea but they asked if the mouthwash could be used in other areas of the body such as the urethra or anus, which we don’t recommend,” Dr Chow said. “Also, we’re not saying just use the mouthwash and not condoms – the majority of gonorrheal infection occur in saliva in kissing and we recommend using mouthwash for this but we actively support using condoms too,” Dr Chow said.


Chow EPF, Walker S, Hocking JS, Bradshaw CS, Chen MY,  Maddaford K, Read TRH, Zhang L, Cornelisse VJ,  Fairley CK. A multicentre double-blind randomised controlled trial evaluating the efficacy of daily use of antibacterial mouthwash against oropharyngeal gonorrhoea among men who have sex with men: the OMEGA (Oral Mouthwash use to Eradicate Gonorrhoea) study protocol. BMC Infect Dis. 2017 Jun 28;17(1):456. doi: 10.1186/s12879-017-2541-3.

Zhang L, Regan DG, Chow EPF, Gambhir M, Cornelisse V, Grulich A, Ong J, Lewis DA, Hocking J, Fairley CK. Neisseria gonorrhoeae Transmission Among Men Who Have Sex With Men: An Anatomical Site-Specific Mathematical Model Evaluating the Potential Preventive Impact of Mouthwash. Sex Transm Dis. 2017 Oct;44(10):586-592. doi: 10.1097/OLQ.0000000000000661.

Bernstein KT, Chesson H, Kirkcaldy RD, Marcus, JL, Gift TL, Aral, SO. Kiss and Tell: Limited Empirical Data on Oropharyngeal Neisseria gonorrhoeae Among Men Who Have Sex With Men and Implications for Modeling. Sexually Transmitted Diseases. 2017 Oct;44(10):596–598.doi: 10.1097/OLQ.0000000000000709

Chow EPF, Walker S, Read TRH, Chen MY, Bradshaw CS, Fairley CK. Self-Reported Use of Mouthwash and Pharyngeal Gonorrhoea Detection by Nucleic Acid Amplification Test. Sexually Transmitted Diseases. 2017 Oct;44(10):593-595. doi: 10.1097/OLQ.0000000000000654.

Chow EPF, Fairley CK. Could antiseptic mouthwash inhibit pharyngeal Neisseria gonorrhoeae? Further research is required. Sex Transm Infect. 2017 Sep;93(6):403. doi: 10.1136/sextrans-2017-053139.

http://ccsmonash.blogspot.com.au/2017/02/trial-into-mouthwash-treatment-for.html#more