Projecting the development of antimicrobial resistance in Neisseria gonorrhoeae from antimicrobial surveillance data: a mathematical modelling study.

BACKGROUND: The World Health Organization recommends changing the first-line antimicrobial treatment for gonorrhoea when ≥ 5% of Neisseria gonorrhoeae cases fail treatment or are resistant. Susceptibility to ceftriaxone, the last remaining treatment option has been decreasing in many countries. We used antimicrobial resistance surveillance data and developed mathematical models to project the time to reach the 5% threshold for resistance to first-line antimicrobials used for N. gonorrhoeae. METHODS: We used data from the Gonococcal Resistance to Antimicrobials Surveillance Programme (GRASP) in England and Wales from 2000-2018 about minimum inhibitory concentrations (MIC) for ciprofloxacin, azithromycin, cefixime and ceftriaxone and antimicrobial treatment in two groups, heterosexual men and women (HMW) and men who have sex with men (MSM). We developed two susceptible-infected-susceptible models to fit these data and produce projections of the proportion of resistance until 2030. The single-step model represents the situation in which a single mutation results in antimicrobial resistance. In the multi-step model, the sequential accumulation of resistance mutations is reflected by changes in the MIC distribution. RESULTS: The single-step model described resistance to ciprofloxacin well. Both single-step and multi-step models could describe azithromycin and cefixime resistance, with projected resistance levels higher with the multi-step than the single step model. For ceftriaxone, with very few observed cases of full resistance, the multi-step model was needed to describe long-term dynamics of resistance. Extrapolating from the observed upward drift in MIC values, the multi-step model projected ≥ 5% resistance to ceftriaxone could be reached by 2030, based on treatment pressure alone. Ceftriaxone resistance was projected to rise to 13.2% (95% credible interval [CrI]: 0.7-44.8%) among HMW and 19.6% (95%CrI: 2.6-54.4%) among MSM by 2030. CONCLUSIONS: New first-line antimicrobials for gonorrhoea treatment are needed. In the meantime, public health authorities should strengthen surveillance for AMR in N. gonorrhoeae and implement strategies for continued antimicrobial stewardship. Our models show the utility of long-term representative surveillance of gonococcal antimicrobial susceptibility data and can be adapted for use in, and for comparison with, other countries.

The Ongoing Impact of COVID-19 on Testing for and Diagnoses of HIV and Bacterial Sexually Transmitted Infections in Oregon.

BACKGROUND: The COVID-19 pandemic has disrupted HIV and sexually transmitted infection (STI) testing accessibility. We sought to assess the longer-term impacts of COVID-19 on HIV and STI testing and diagnosis in Oregon. METHODS: First, we examined HIV, Neisseria gonorrhoeae / Chlamydia trachomatis (CT), and syphilis tests conducted at the Oregon State Public Health Laboratory (public sector) and a large commercial laboratory (private sector) and HIV, N. gonorrhoeae , CT, and primary and secondary (P&S) syphilis diagnoses in Oregon from January 1, 2019, to December 31, 2021. We compared monthly testing and diagnosis rates in 5 prespecified periods: pre-COVID-19 (January 2019-February 2020), stay-at-home order (March 2020-May 2020), reopening (June 2020-December 2020), vaccine availability (January 2021-June 2021), and Delta/early Omicron spread (July 2021-December 2021). Second, we calculated the number of HIV and STI diagnoses per test in the public and private sectors. Finally, we used seasonal autoregressive integrated moving average models to predict expected HIV and STI diagnoses for comparison to those observed. RESULTS: Both public and private sector HIV and bacterial STI testing fell to nadirs in April 2020 with incomplete recovery to 2019 levels by the close of 2021. Compared with pre-COVID-19, public sector and private sector testing was significantly lower in all subsequent periods. Compared with pre-COVID-19, P&S syphilis cases were 52%, 75%, and 124% greater in the reopening, vaccine availability, and Delta/early Omicron periods, respectively. From March 2020 to December 2021, we observed an excess of P&S syphilis cases (+37.1%; 95% confidence interval, 22.2% to 52.1%) and a deficit in CT cases (-10.7%; 95% confidence interval, -15.4% to -6.0%). CONCLUSIONS: By December 2021, HIV/STI testing had not recovered to pre-COVID-19 levels, and HIV/STI continues to be underdiagnosed. Despite decreased testing, P&S syphilis cases have increased substantially.

Prevalence of five curable sexually transmitted infections and associated risk factors among tertiary student men who have sex with men in Nairobi, Kenya: a respondent-driven sampling survey†.

BACKGROUND: Young men who have sex with men (MSM) are a key population at high risk of sexually transmitted infections (STIs). We conducted a respondent-driven sampling (RDS) bio-behavioural survey to estimate the prevalence of five curable STIs: chlamydia, gonorrhoea, syphilis, trichomoniasis and Mycoplasma genitalium infection, and associated risk factors among tertiary student MSM (TSMSM) in Nairobi, Kenya. METHODS: Between February and March 2021, we recruited 248 TSMSM aged ≥18years who self-reported engaging in anal and/or oral sex with another man in the past year. Samples collected included urine, anorectal and oropharyngeal swabs for pooled Chlamydia trachomatis , Mycoplasma genitalium , Neisseria gonorrhoeae and Trichomonas vaginalis testing using multiplex nucleic acid amplification tests, and venous blood for serological Treponema pallidum screening and confirmation of current infection. Participants self-completed a behavioural survey on a REDCap digital platform. Data analysis was done using RDS-Analyst (v0.72) and Stata (v15). Differences in proportions were examined using the chi-squared (χ 2 ) test, and unweighted multivariate logistic regression was used to assess factors associated with STI prevalence. RESULTS: RDS-adjusted prevalence rates of at least one of the five STIs, chlamydia, gonorrhoea, Mycoplasma genitalium infection, trichomoniasis and latent syphilis were 58.8%, 51.0%, 11.3%, 6.0%, 1.5% and 0.7%, respectively. Factors independently associated with STI prevalence were inconsistent condom use (adjusted odds ratio (AOR)=1.89, 95% confidence interval (CI): 1.03-3.47, P =0.038) and the last sex partner being a regular partner (AOR=2.35, 95% CI: 1.12-4.92, P =0.023). CONCLUSION: STI prevalence among TSMSM in Nairobi, Kenya, is disturbingly high, demonstrating urgent need for tailored testing, treatment and prevention interventions for this population.

Decreased Neisseria gonorrhoeae genotypic diversity following COVID-19 restrictions in Queensland, Australia 2020.

We investigated the potential effects of COVID-19 public health restrictions on the prevalence and distribution of Neisseria gonorrhoeae (NG) genotypes in our Queensland isolate population in the first half of the year 2020. A total of 763 NG isolates were genotyped to examine gonococcal strain distribution and prevalence for the first 6 months of 2020, with 1 January 2020 to 31 March 2020 classified as 'pre' COVID-19 restrictions (n = 463) and 1 April 2020 to 30 June 2020 classified as 'post' COVID-19 restrictions (n = 300). Genotypes most prevalent 'pre' restrictions remained proportionally high 'post' restrictions, with some significantly increasing 'post' restrictions. However, genotype diversity was significantly reduced 'post' restrictions. Overall, it seems public health restrictions (9-10 weeks) were not sufficient to affect rates of infection or reduce the prevalence of well-established genotypes in our population, potentially due to reduced access to services or health-seeking behaviours.

Conductive Ink-Coated Paper-Based Supersandwich DNA Biosensor for Ultrasensitive Detection of Neisseria gonorrhoeae.

Herein, we report results of the studies relating to the development of an impedimetric, magnetic bead-assisted supersandwich DNA hybridization assay for ultrasensitive detection of Neisseria gonorrhoeae, the causative agent of a sexually transmitted infection (STI), gonorrhea. First, a conductive ink was formulated by homogenously dispersing carboxylated multiwalled carbon nanotubes (cMWCNTs) in a stable emulsion of terpineol and an aqueous suspension of carboxymethyl cellulose (CMC). The ink, labeled C5, was coated onto paper substrates to fabricate C5@paper conductive electrodes. Thereafter, a magnetic bead (MB)-assisted supersandwich DNA hybridization assay was optimized against the porA pseudogene of N. gonorrhoeae. For this purpose, a pair of specific 5' aminated capture probes (SCP) and supersandwich detector probes (SDP) was designed, which allowed the enrichment of target gonorrheal DNA sequence from a milieu of substances. The SD probe was designed such that instead of 1:1 binding, it allowed the binding of more than one T strand, leading to a 'ladder-like' DNA supersandwich structure. The MB-assisted supersandwich assay was integrated into the C5@paper electrodes for electrochemical analysis. The C5@paper electrodes were found to be highly conductive by a four-probe conductivity method (maximum conductivity of 10.1 S·cm-1). Further, the biosensing assay displayed a wide linear range of 100 aM-100 nM (109 orders of magnitude) with an excellent sensitivity of 22.6 kΩ·(log[concentration])-1. The clinical applicability of the biosensing assay was assessed by detecting genomic DNA extracted from N. gonorrhoeae in the presence of DNA from different non-gonorrheal bacterial species. In conclusion, this study demonstrates a highly sensitive, cost-effective, and label-free paper-based device for STI diagnostics. The ink formulation prepared for the study was found to be highly thixotropic, which indicates that the paper electrodes can be screen-printed in a reproducible and scalable manner.

Increased clonality among Neisseria gonorrhoeae isolates during the COVID-19 pandemic in Amsterdam, the Netherlands.

Distancing measures during the COVID-19 lockdown led to a temporary decrease of casual sex partners among clients of the Centre for Sexual Health (CSH) in Amsterdam, the Netherlands. We investigated the effect of this change on the genotypic and phenotypic distribution of Neisseria gonorrhoeae (Ng) isolates from CSH patients. From each Ng-positive patient we sequenced one isolate, resulting in 322 isolates which constituted two groups: 181 isolates cultured from 15 January to 29 February 2020 (before the first lockdown) and 141 cultured from 15 May to 30 June 2020 (during the first lockdown). Patient characteristics showed significantly more symptomatic patients and significantly fewer reported sex partners during the lockdown. Phenotypic data showed an increase in low-level azithromycin resistance and ceftriaxone susceptibility during the lockdown, and this remained after the study period. The diversity in sequence types (STs) decreased slightly during the lockdown. A shift occurred from ST 8156 being predominant before lockdown to ST 9362 during lockdown and a remarkably low median SNP distance of 17 SNPs was found between ST 9362 isolates obtained during lockdown. These findings reflect restricted travel and the change in sexual behaviour of CSH clients during the lockdown, with a potentially increased local transmission of the ST 9362 strain during this period, which led to genotypic and phenotypic changes in the Ng population. This shows that public health measures have far-reaching consequences and should be considered in the surveillance of other infectious diseases.

The European response to control and manage multi- and extensively drug-resistant Neisseria gonorrhoeae.

Because cefixime and ceftriaxone resistance in Neisseria gonorrhoeae and gonorrhoea treatment failures were increasing, a response plan to control and manage multidrug-resistant N. gonorrhoeae (MDR-NG) in Europe was published in 2012. The three main areas of the plan were to: (i) strengthen surveillance of antimicrobial resistance (AMR), (ii) implement monitoring of treatment failures and (iii) establish a communication strategy to increase awareness and disseminate AMR results. Since 2012, several additional extensively drug-resistant N. gonorrhoeae (XDR-NG) strains have emerged, and strains with high-level ceftriaxone resistance spread internationally. This prompted an evaluation and review of the 2012 European Centre for Disease Prevention and Control (ECDC) response plan, revealing an overall improvement in many aspects of monitoring AMR in N. gonorrhoeae; however, treatment failure monitoring was a weakness. Accordingly, the plan was updated in 2019 to further support European Union/European Economic Area (EU/EEA) countries in controlling and managing the threat of MDR/XDR-NG in Europe through further strengthening of AMR surveillance and clinical management including treatment failure monitoring. The plan will be assessed biennially to ensure its effectiveness and its value. Along with prevention, diagnostic, treatment and epidemiological surveillance strategies, AMR surveillance is essential for effective control of gonorrhoea.

18 months on: an interrupted time series analysis investigating the effect of COVID-19 on chlamydia and gonorrhoea testing and test positivity at the Gold Coast, Australia.

BACKGROUND: STI rates have been reported as reduced during the height of the COVID-19 pandemic. Our study evaluates the number of Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) infections recorded relative to the number of tests performed in 2017-2021, thus accurately depicting trends over time and evaluate the effect of COVID-19 restrictions since these were implemented in March 2020. METHODS: Data was extracted from an electronic database of pathology and clinical records used at Gold Coast Sexual Health Service (GCSHS) in Queensland, Australia from January 2017 to October 2021. Poisson regression-based interrupted time series analyses were performed for number of tests performed and test positivity over the study period. The COVID-19 period was defined as starting from March 2020 when public health directives were implemented. RESULTS: CT and NG testing dropped significantly in the month after COVID-19 restrictions were brought in, by 30% and 23% respectively. Over the 5year study period, the proportion of positive CT tests has consistently decreased by approximately 0.33% points per year (P ≤0.001). The instigation of COVID-19 restrictions had no effect on this trend. The proportion of NG positive tests remained steady prior to COVID-19 (P =0.96) at approximately 3.5%, decreased immediately at the onset of COVID-19 restrictions to approximately 2.5% (P <0.001) and has remained at this level post-COVID restrictions (P =0.54). Testing at GCSHS continued to target gay and bisexual men, accounting for ≥50% of all tests performed. CONCLUSION: Our study suggests that there has been a sustained reduction in test positivity of NG infections in the 18months since COVID-19 restrictions were implemented, and that this is not an artifact of reduced testing. It highlights the importance of maintaining health messaging including screening for sexually transmissible infections and maintaining access to services, which may include alternative models of care such as Telehealth, self-testing and collaboration between all sexual health service providers.

The diagnostic accuracy of pooled testing from multiple individuals for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae: a systematic review.

OBJECTIVES: Molecular testing for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) is costly. Therefore, we appraised the evidence regarding pooling samples from multiple individuals to test for CT/NG. METHODS: In this systematic review, we searched 5 databases (2000-2021). Studies were included if they contained primary data describing pooled testing. We calculated the pooled sensitivities and specificities for CT and NG using a bivariate mixed-effects logistic regression model. RESULTS: We included 22 studies: most were conducted in high-income countries (81.8%, 18 of 22), among women (73.3%, 17 of 22), and pooled urine samples (63.6%, 14 of 22). Eighteen studies provided 25 estimates for the meta-analysis of diagnostic accuracy, with data from 6,913 pooled specimens. The pooled sensitivity for CT was 98.4% (95% confidence intervals [CI]: 96.8-99.2%, I2=77.5, p<0.001), and pooled specificity was 99.9% (95% CI: 99.6-100.0%, I2=62.6, p<0.001). Only 2 studies reported pooled testing for NG, and both reported similarly high sensitivity and specificity as for CT. Sixteen studies provided data on the cost of pooling, reporting cost-savings ranging from 39%-90%. CONCLUSIONS: Pooled testing from multiple individuals for CT is highly sensitive and specific compared with individual testing. This approach has the potential to reduce the cost of screening in populations for which single anatomic site screening is recommended.

Changes in testing and incidence of Chlamydia trachomatis and Neisseria gonorrhoeae - the possible impact of the COVID-19 pandemic in the three Scandinavian countries.

BACKGROUND: This study aimed to investigate what impact the COVID-19 pandemic and its associated restrictions had on Chlamydia trachomatis and Neisseria gonorrhoeae infections in Sweden, Denmark and Norway, countries with very different governmental strategies for handling this pandemic. METHODS: Retrospective analysis of data collected via requests to Swedish regions and to health authorities in Denmark and Norway. The data were collected for the years 2018-2020 and the data from Sweden were more detailed. RESULTS: When the pandemic restrictions were installed in 2020, the number of reported chlamydia cases decreased. The decline was most pronounced in Norway 10.8% (2019: n = 28,446; 2020: n = 25,444) while it was only 3.1% in Denmark (2019: n = 35,688; 2020: n = 34,689) and 4.3% in Sweden (2019: n = 34,726; 2020: n = 33,339). Nucleic acid amplifications tests for chlamydia decreased in Sweden (10%) and Norway (18%) in 2020 compared to 2019, while in Denmark a 21% decrease was noted in April 2020 but thereafter increased to a higher level than 2019. The number of reported gonorrhoea cases decreased in Sweden (17%) and in Norway (39%) in 2020 compared to 2019, while a 21% increase was noted in Denmark. CONCLUSIONS: Pandemic restrictions had an impact on the number of reported chlamydia infections in all three countries, but only temporarily and did not seem to be correlated to the restriction levels. The number of reported gonorrhoea infections in Sweden and Norway significantly decreased but not in Denmark. Pandemic restrictions appear to have had a limited effect on the spread of chlamydia and gonorrhoea.

Sampling time for self-taking an oropharyngeal swab for gonorrhoea and chlamydia testing.

Self-taking oropharyngeal swabs for sexually transmitted infections such as gonorrhoea and chlamydia has become more common during the COVID-19 pandemic to minimise the risk to healthcare workers. However, there have been no standardised guidelines on sampling time for taking an oropharyngeal swab for gonorrhoea and chlamydia testing. We recruited 215 participants at the Melbourne Sexual Health Centre, Australia, between November 2021 and January 2022. We asked participants to report the time they spent on self-taking the oropharyngeal swab. The median self-taking sampling time was 8s (IQR=5-12), and the time did not differ between oropharyngeal gonorrhoea positivity (P =0.570) and oropharyngeal chlamydia positivity (P =0.457).

Community-Based Prevalence Estimates of Chlamydia trachomatis and Neisseria gonorrhoeae Infections Among Gay, Bisexual, and Other Men Who Have Sex With Men in Montréal, Canada.

BACKGROUND: Reported cases of Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) infections are increasing among Canadian men. Estimates of community-based CT/NG prevalence are lacking among gay, bisexual, and other men who have sex with men (GBM). METHODS: Respondent driven sampling was used to recruit GBM in Montréal, Canada between February 2017 and June 2018. Specimens provided from urogenital, rectal, and pharyngeal sites were analyzed using nucleic acid amplification test to detect CT/NG. Prevalence estimates of CT/NG, overall and by anatomical site were calculated. All estimates are respondent-driven sampling-adjusted. RESULTS: Among 1177 GBM, the prevalence of rectal, urogenital, pharyngeal and overall were respectively 2.4%, 0.4%, 0.4%, and 2.8% for CT infections, and 3.1%, 0.4%, 3.5%, and 5.6% for NG infections. If testing had been limited to the urogenital site, 80% and 94% of CT and NG infections, respectively, would have been missed. CONCLUSIONS: This community-based study among GBM shows that the CT prevalence was about half of that observed for NG. A large part of CT/NG infections involves only the extragenital sites, highlighting the need for systematic multisite screening regardless of symptoms. In the mist of the COVID-19 pandemic and the limited CT/NG screening capacity due to test kits shortage, it might be considered to prioritize rectal and pharyngeal CT/NG testing over urogenital testing in asymptomatic GBM.

Unusual presentation of a periurethral abscess following infection with Neisseria gonorrhoea.

We describe an unusual case of a male patient presenting with penile and testicular swelling following an unprotected and traumatic sexual encounter. It was suspected that an isolated penile injury occurred during intercourse; however, ultrasound imaging identified an intact tunical layer and right-sided epididymo-orchitis. Following screening for sexually transmitted infections (STIs), he was discharged with antibiotics and advice to attend the Sexual Health Centre for contact tracing. He represented with a periurethral abscess and an antimicrobial-resistant (AMR) strain of Neisseria gonorrhoea was identified. Appropriate antibiotic treatment was initiated. Examination-under-anaesthesia, following abscess drainage, revealed a contained collection with no urethral fistula; however, a flat urethral lesion was seen during urethroscopy. Repeat urethroscopy and biopsy of the lesion indicated polypoid urethritis. Periurethral abscess secondary to gonococcal urethritis is a rare complication, but one that we should be suspicious of, especially with the growing incidence of AMR-STIs.

Potential impact of the COVID-19 pandemic on the national and regional incidence, epidemiology and diagnostic testing of chlamydia and gonorrhoea in Sweden, 2020.

The COVID-19 pandemic has challenged the societies and health care systems globally, and resulted in many social and physical distancing restrictions to limit the spread of SARS-CoV-2. These restrictions have also likely affected the frequency of intimate contacts and the spread of sexually transmitted infections (STIs). Compared to most other countries, Sweden especially in Spring-Autumn 2020 pursued mainly milder voluntary, that is, not mandatory enforced by laws, recommended restrictions and the impacts of these on society and spread of STIs remain largely unknown. We describe the potential impact of the COVID-19 pandemic on the national and regional incidence, epidemiology and diagnostic testing of chlamydia and gonorrhoea in Sweden in 2020. Compared to 2019, we found a significant decrease in incidence of chlamydia (-4.5%) and gonorrhoea (-17.5%), and in diagnostic testing (-10.5% for chlamydia, -9.4% for gonorrhoea) in 2020. However, the decrease in chlamydia incidence, which has mainly been decreasing in the last 10 years, was not significant when compared with the average incidence in 2017-2019. The largest decrease in national incidence of both infections was observed among young and heterosexual patients, however, some Swedish regions showed an increased incidence, particularly of chlamydia. Increased "internet-based self-sampling" testing approach partly compensated for a decreased attendance at STI clinics. Studies, including sexual behaviour, prevention, reasons for attending STI health care, STIs in different anatomical sites and management of STIs, are required to elucidate the impact of COVID-19-associated social and physical distancing restrictions on sexual activity and the incidence and epidemiology of chlamydia and gonorrhoea in Sweden.

At-Home Specimen Self-Collection and Self-Testing for Sexually Transmitted Infection Screening Demand Accelerated by the COVID-19 Pandemic: a Review of Laboratory Implementation Issues.

The coronavirus disease 2019 (COVID-19) pandemic reduced the sexually transmitted infection (STI) testing volume due to social-distancing and stay-at-home orders, among other reasons. These events highlighted previously known benefits of at-home STI self-testing or specimen self-collection and accelerated testing demand via telemedicine. We review testing outside traditional clinical settings. We focus on three curable bacterial STIs among the top 10 U.S. nationally notifiable conditions with screening recommendations: syphilis, gonorrhea (Neisseria gonorrhoeae, also known as the gonococcus [GC]), and chlamydia (Chlamydia trachomatis). At least 19 million GC/C. trachomatis (GC/CT) screening or diagnostic tests are performed annually, presenting a considerable challenge during the pandemic. Unlike for HIV, STI at-home tests are currently not commercially available. However, innovative telemedicine providers currently offer services where specimen self-collection kits are mailed to patients at home who then ship them to laboratories for processing. We discuss technical and regulatory aspects of modifications for home-based specimen self-collection. The telemedicine provider typically manages and communicates results, provides linkage to care, and is responsible for billing and case reporting. We also describe rapid testing devices in development that may present an opportunity for future self-testing. In summary, COVID-19 has accelerated the evaluation and development of STI self-tests and specimen self-collection. The remaining obstacles are high price, regulatory approval, support for laboratories offering the service, and uncertainty regarding whether target populations with the greatest need are reached effectively. However, increased testing, convenience, and privacy are potential benefits that may enhance uptake and outlast the pandemic.

Potential effect of antiseptic mouthwash on the incidence of Neisseria gonorrhoeae among men who have sex with men: a mathematical modelling study.

OBJECTIVES: The incidence of Neisseria gonorrhoeae and its antimicrobial resistance is increasing in many countries. Antibacterial mouthwash may reduce gonorrhoea transmission without using antibiotics. We modelled the effect that antiseptic mouthwash may have on the incidence of gonorrhoea. DESIGN: We developed a mathematical model of the transmission of gonorrhoea between each anatomical site (oropharynx, urethra and anorectum) in men who have sex with men (MSM). We constructed four scenarios: (1) mouthwash had no effect; (2) mouthwash increased the susceptibility of the oropharynx; (3) mouthwash reduced the transmissibility from the oropharynx; (4) the combined effect of mouthwash from scenarios 2 and 3. SETTING: We used data at three anatomical sites from 4873 MSM attending Melbourne Sexual Health Centre in 2018 and 2019 to calibrate our models and data from the USA, Netherlands and Thailand for sensitivity analyses. PARTICIPANTS: Published available data on MSM with multisite infections of gonorrhoea. PRIMARY AND SECONDARY OUTCOME MEASURES: Incidence of gonorrhoea. RESULTS: The overall incidence of gonorrhoea was 44 (95% CI 37 to 50)/100 person-years (PY) in scenario 1. Under scenario 2 (20%-80% mouthwash coverage), the total incidence increased (47-60/100 PY) and at all three anatomical sites by between 7.4% (5.9%-60.8%) and 136.6% (108.1%-177.5%). Under scenario 3, with the same coverage, the total incidence decreased (20-39/100 PY) and at all anatomical sites by between 11.6% (10.2%-13.5%) and 99.8% (99.2%-100%). Under scenario 4, changes in the incidence depended on the efficacy of mouthwash on the susceptibility or transmissibility. The effect on the total incidence varied (22-55/100 PY), and at all anatomical sites, there were increases of nearly 130% and large declines of almost 100%. CONCLUSIONS: The effect of mouthwash on gonorrhoea incidence is largely predictable depending on whether it increases susceptibility to or reduces the transmissibility of gonorrhoea.