Chlamydia trachomatis transmission between the oropharynx, urethra and anorectum in men who have sex with men: a mathematical model

Estimating Partnership Duration among MSM in Belgium-A Modeling Study

Mathematical modeling is widely used for describing infection transmission and evaluating interventions. The lack of reliable social parameters in the literature has been mentioned by many modeling studies, leading to limitations in the validity and interpretation of the results. Using data from the European MSM Internet survey 2017, we developed a network model to describe sex acts among MSM in Belgium. The model simulates daily sex acts among steady, persistent casual and one-off partners in a population of 10,000 MSM, grouped as low- or high-activity by using three different definitions. Model calibration was used to estimate partnership duration and homophily rates to match the distribution of cumulative sex partners over 12 months. We estimated an average duration between 1065 and 1409 days for steady partnerships, 4-6 and 251-299 days for assortative high- and low-activity individuals and 8-13 days for disassortative persistent casual partnerships, respectively, varying across the three definitions. High-quality data on social network and behavioral parameters are scarce in the literature. Our study addresses this lack of information by providing a method to estimate crucial parameters for network specification.

Sexually transmitted coinfections among at-risk HIV-positive MSM: implications for optimal preemptive treatment

Background

Concurrent sexually transmitted infections (STIs) are common in sexually active populations. We aimed to estimate the prevalence and coinfection rates of bacterial STIs among sexually active, HIV-positive men who have sex with men (MSM), and to assess the potential benefits of different combination treatment regimens in managing concurrent bacterial STIs.

Methods

From September 2021 to September 2023, HIV-positive MSM underwent STI testing when they had symptoms suggestive of STIs or recently acquired hepatitis C virus (HCV) infection or early syphilis. The oral rinse, rectal swab, and urethral swab specimens were tested for Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma spp., Ureaplasma spp., and Trichomonas vaginalis with the use of multiplex real-time polymerase-chain-reaction assays. The estimated coinfection rates were used to evaluate the benefits of different combination treatment regimens for managing coinfections.

Results

During the study period, 535 participants (median age, 37 years; and CD4 count, 615 cells/mm3) were enrolled. On their first visits, at least one bacterial pathogen was detected in 57.9% and concomitant bacterial infections were found in 32.9% of the participants. The most commonly identified pathogen was U. urealyticum (36.3%), followed by C. trachomatis (22.8%), and N. gonorrhoeae (19.8%). The factors associated with any bacterial STIs included older age (per 1-year increase, adjusted odds ratio [AOR], 0.97; 95% confidence interval [CI], 0.95-1.00), early syphilis (AOR, 1.87; 95% CI, 1.22-2.84), and having more than 5 sex partners in the preceding 3 months (AOR, 2.08, 95% CI, 1.07-4.06). A combination therapy of benzathine penicillin G with a 7-day course of doxycycline could simultaneously treat 27.1% of C. trachomatis coinfections in participants with early syphilis, while a combination therapy of ceftriaxone with doxycycline could simultaneously treat 40.6% of chlamydial coinfections in participants with gonorrhea.

Conclusion

Bacterial STIs were prevalent and concomitant infections were not uncommon among sexually active, HIV-positive MSM, supporting regular screening for bacterial STIs. The effectiveness of preemptive use of doxycycline as combination therapy for concurrent STIs warrants more investigations.

STI pathogens in the oropharynx: update on screening and treatment

PURPOSE OF REVIEW

The rise in antimicrobial resistance in several STI pathogens such as Neisseria gonorrhoeae has become a public health threat as only one first-line treatment remains. Reducing screening interval for gonorrhoea and chlamydia in high-prevalence populations has been proposed to address antimicrobial stewardship, but this remains controversial. This review aimed to revisit the epidemiology of infections at the oropharynx and review the current screening recommendations and treatment guidelines in different populations.

RECENT FINDINGS

Emerging evidence suggests that the oropharynx is the primary anatomical site for gonorrhoea transmission but maybe not for chlamydia transmission. Most international guidelines recommend 3-monthly oropharyngeal gonorrhoea and chlamydia screening for high-prevalence populations (e.g. men who have sex with men) but not low-prevalence populations (e.g. heterosexuals) given the clinical and public health benefits of screening in low-prevalence populations are still unclear. Doxycycline remains the first-line treatment for oropharyngeal chlamydia in most guidelines. However, some countries have moved from dual therapy (ceftriaxone and azithromycin) to monotherapy (ceftriaxone) for oropharyngeal gonorrhoea treatment to address antimicrobial stewardship.

SUMMARY

The transmission of gonorrhoea and chlamydia is still not fully understood. Further work will be required to evaluate the benefits and harms of reducing screening in high-prevalence populations.

Update on the Epidemiology, Screening, and Management of Chlamydia trachomatis Infection

Chlamydia trachomatis infection ("chlamydia") is the most commonly diagnosed bacterial sexually transmitted infection globally, occurring in the genitals (urethra or vagina/cervix), rectum, or pharynx. If left untreated in women, genital chlamydia can ascend into the upper genital tract causing pelvic inflammatory disease, increasing their risk for ectopic pregnancy, infertility, and chronic pelvic pain. In men, chlamydia can cause epididymitis and proctitis. However, chlamydia is asymptomatic in over 80% of cases. This article provides an update on the epidemiology, natural history, and clinical manifestations of chlamydia in adults and discusses the current approaches to its management and control policy.

Incidence and Duration of Pharyngeal Chlamydia Among a Cohort of Men Who Have Sex With Men

BACKGROUND

The prevalence of pharyngeal chlamydia is low, but its incidence and duration are unknown. A high incidence or duration may support the role of pharyngeal chlamydia in sustaining chlamydia transmission.

METHODS

From March 2016 to December 2018, we enrolled men who have sex with men (MSM) in a 48-week cohort study in Seattle, Washington. Participants self-collected pharyngeal specimens weekly. We tested specimens using nucleic acid amplification testing at the conclusion of the study. In primary analyses, we defined incident pharyngeal chlamydia as >2 consecutive weeks of a positive pharyngeal specimen. In sensitivity analyses, we defined incident chlamydia as >1 week of a positive specimen. We estimated duration of pharyngeal chlamydia, censoring at loss to follow-up, receipt of antibiotics, or end of study.

RESULTS

A total of 140 participants contributed 70.5 person-years (PY); 1.4% had pharyngeal chlamydia at enrollment. In primary analyses, there were 8 pharyngeal chlamydia cases among 6 MSM (incidence = 11.4 per 100 PY; 95% confidence interval [CI]: 6.0-21.9). In sensitivity analysis, there were 19 cases among 16 MSM (incidence = 27.1 per 100 PY; 95% CI: 18.5-39.8). The median duration was 6.0 weeks (95% CI: 2.0-undefined) in primary analysis and 2.0 weeks (95% CI: 1.1-6.0) in sensitivity analysis. Duration was shorter for those with a history of chlamydia compared with those without (3.6 vs 8.7 weeks; P = .02).

CONCLUSIONS

Pharyngeal chlamydia has a low incidence and duration relative to other extragenital sexually transmitted infections. Its contribution to population-level transmission remains unclear.

Controversies and evidence on Chlamydia testing and treatment in asymptomatic women and men who have sex with men: a narrative review

Background

Chlamydia trachomatis (CT) is the most common bacterial sexually transmitted infection (STI) worldwide. CT is mainly asymptomatic. Test-and-treat strategies are widely implemented to prevent transmission and complications. Strategies are not without controversy in asymptomatic women and men who have sex with men (MSM). Concerns are emerging to test and treat asymptomatic persons for urogenital CT (‘Controversy 1’) and pharyngeal or rectal CT (‘Controversy 2’), whereby testing symptomatic persons is not under debate. Opposed views in CT treatment involve using azithromycin versus doxycycline (‘Controversy 3’). The objective of this review is to provide coverage of these public health and clinical controversies by reviewing the current scientific evidence.

Methods

A literature search was performed using PubMed for relevant publications between 2018 and September 2021, and iterative retrieval of additional relevant publications.

Results

Controversy 1. In women, the majority of asymptomatic CT are at the urogenital site, and detections mostly include viable CT. CT easily transmits to a partner and potentially also between the vaginal and rectal areas; the clinical impact of urogenital CT is established, although risks for adverse outcomes are uncertain. Wide-scale testing in asymptomatic women has not resulted in reduced prevalence. In MSM, evidence for the clinical impact of asymptomatic urogenital CT is lacking. Controversy 2. Rectal CT is common in women diagnosed with urogenital CT, but the clinical impact of asymptomatic rectal CT is uncertain. In MSM, rectal CT is common, and most CT infections are at the rectal site, yet the risk of longer term complications is unknown. In both sexes, pharyngeal CT is uncommon and has no documented clinical impact. Controversy 3. In the treatment of rectal CT, doxycycline has superior effectiveness to azithromycin. Evidence has also accumulated on the harms of test-and-treat strategies.

Conclusions

Current practices vary widely, from widescale test-and-treat approaches to more individual patient- and partner-level case management. Choosing which asymptomatic people to test at what anatomic site, and whether to test or not, requires an urgent (re-)definition of the goals of testing and treating asymptomatic persons. Treatment guidelines are shifting toward universal doxycycline use, and clinical practice now faces the challenge of implementation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-022-07171-2.

Test-and-treat is a key strategy in the control of Chlamydia trachomatis (CT). We discuss recent controversies and present scientific evidence regarding urogenital, rectal, and pharyngeal CT test-and-treat strategies in women and in men who have sex with men (MSM). This should inform best practices for the prevention and management of the most common bacterial sexually transmitted infection (STI) worldwide.

Modelling the potential role of saliva use during masturbation in the transmission of Neisseria gonorrhoeae at multiple anatomical sites

Background Neisseria gonorrhoeae can be cultured from saliva in men with pharyngeal gonorrhoea and could theoretically be transmitted from the pharynx to the urethra when saliva is used as a lubricant for masturbation. In this work, we proposed that saliva use during masturbation may be a potential transmission route of gonorrhoea. Methods We analysed the transmission of Neisseria gonorrhoeae at the oropharynx, urethra and anorectum with mathematical models among men who have sex with men using data from six different studies. Model 1 included transmission routes (oral sex, anal sex, rimming, kissing, and three sequential sex practices). In Model 2, we added saliva use during solo masturbation and mutual masturbation to model 1. Results Model 2 could replicate single site infection at the oropharynx, urethra and anorectum and multi-site infection across six different datasets. However, the calibration of Model 2 was not significantly different from Model 1 across four datasets. Model 2 generated an incidence of gonorrhoea from masturbation of between 5.2% (95% CI: 3.2-10.1) to 10.6% (95% CI: 5.8-17.3) across six data sets. Model 2 also estimated that about one in four cases of urethral gonorrhoea might arise from solo masturbation and mutual masturbation. Conclusions Our models raise the possibility that saliva use during masturbation may play a role in transmitting gonorrhoea. This is an important area to explore because it contributes to the knowledge base about gonorrhoea transmission.

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.

Modelling the multiple anatomical site transmission of Mycoplasma genitalium among men who have sex with men in Australia

Mycoplasma genitalium (M. genitalium) is a recently recognised and important sexually transmitted infection among men who have sex with men (MSM). The role of oral sex, rimming, and kissing on M. genitalium transmission in MSM is unclear. We created four deterministic susceptible-infectious-susceptible epidemic models to examine the role that different sexual behaviours play in transmitting M. genitalium at the oropharynx, urethra anorectum among men who have sex with men in Australia. Our results suggest that oral and anal sex without other sexual practices (model 1) replicate well single site infection at the oropharynx, urethra and anorectum and also multi-site infection. If kissing or rimming are added to model 1 (i.e., model 2–4) no substantial improvements in the calibration of the models occur. Model 1 estimates that 3.4% of infections occur at the oropharynx, 34.8% at the urethra and 61.8% at the anorectum. Model 1 also estimates that the proportion of incident M. genitalium transmitted by anal sex was 82.4%, and by oral sex was about 17.6%. Our findings could provide an enhanced understanding of M. genitalium transmission in MSM, thus providing insights into what sexual practices contribute most to transmission.

Comparison of the patterns of chlamydia and gonorrhoea at the oropharynx, anorectum and urethra among men who have sex with men

OBJECTIVE

Chlamydia and gonorrhoea are common sexually transmitted infections that infect the oropharynx, anorectum and urethra in men who have sex with men (MSM). This study aimed to examine the pattern of infection at more than one site (multisite) for chlamydia and gonorrhoea among MSM.

METHODS

This was a retrospective study of MSM attending the Melbourne Sexual Health Centre for the first time between 2018 and 2019. We included MSM aged ≥16 years who had tested for Neisseria gonorrhoeae and Chlamydia trachomatis at all three sites (oropharynx, anorectum and urethra). We compared infections that occurred at a single site (termed single-site infection) and those that occurred at more than one site (termed multisite infections).

RESULTS

Of the 3938 men who were tested for chlamydia and gonorrhoea, 498/3938 men (12.6%, 95% CI 11.5% to 13.6%) had chlamydia at any site, of whom 400/498 (80.3%, 95% CI 78.9% to 81.2%) had single-site chlamydia infection, and 98/498 (19.7%, 95% CI 16.2% to 23.1%) had multisite infections. A similar proportion of men had gonorrhoea at any site (447/3938, 11.4%, 95% CI 10.3% to 12.2%), but among these 447 men, single-site infection was less common (256/447, 57.3%, 95% CI 52.6% to 61.7%, p<0.001) and multisite infection (191/447, 42.7%, 95% CI 38.2% to 47.3%, p<0.001) was more common than chlamydia. There were also marked differences by anatomical site. Urethral infection commonly occurred as single sites (75/122, 61.5%, 95% CI 52.8% to 70.1%) for chlamydia but uncommonly occurred for gonorrhoea (12/100, 12.0%, 95% CI 5.6% to 18.3%, p<0.001). In contrast, anorectal infection uncommonly occurred as multisite infection for chlamydia (98/394, 24.9%, 95% CI 20.6% to 29.1%) but was common (184/309, 59.5%, 95% CI 54.0% to 64.9%, p<0.001) for gonorrhoea.

CONCLUSIONS

The markedly different pattern of site-specific infection for chlamydia and gonorrhoea infections among the same MSM suggests significant differences in the transmissibility between anatomical sites and the duration of each infection at each site.

Role of saliva use during masturbation in the transmission of Chlamydia trachomatis in men who have sex with men

Masturbation is a common sexual practice in men, and saliva is often used as a lubricant during masturbation by men who have sex with men. However, the role of saliva use during masturbation in the transmission of chlamydia is still unclear. We developed population-level, susceptible-infected-susceptible compartmental models to explore the role of saliva use during masturbation on the transmission of chlamydia at multiple anatomical sites. In this study, we simulated both solo masturbation and mutual masturbation. Our baseline model did not include masturbation but included transmission routes (anal sex, oral-penile sex, rimming, kissing and sequential sexual practices) we have previously validated (model 1). We added masturbation to model 1 to develop the second model (model 2). We calibrated the model to five clinical datasets separately to assess the effects of masturbation on the prevalence of site-specific infection. The inclusion of masturbation (model 2) significantly worsened the ability of the models to replicate the prevalence of C. trachomatis. Using model 2 and the five data sets, we estimated that saliva use during masturbation was responsible for between 3.9% [95% confidence interval (CI) 2.0–6.8] and 6.2% (95% CI 3.8–10.5) of incident chlamydia cases at all sites. Our models suggest that saliva use during masturbation is unlikely to play a major role in chlamydia transmission between men, and even if it does have a role, about one in seven cases of urethral chlamydia might arise from masturbation.

Modelling the contribution that different sexual practices involving the oropharynx and saliva have on Neisseria gonorrhoeae infections at multiple anatomical sites in men who have sex with men

BACKGROUND

The spectrum of sexual practices that transmit Neisseria gonorrhoeae in men who have sex with men (MSM) is controversial. No studies have modelled potential Neisseria gonorrhoeae transmission when one sexual practice follows another in the same sexual encounter ('sequential sexual practices'). Our aim was to test what sequential practices were necessary to replicate the high proportion of MSM who have more than one anatomical site infected with gonorrhoea ('multisite infection').

METHODS

To test our aim, we developed eight compartmental models. We first used a baseline model (model 1) that included no sequential sexual practices. We then added three possible sequential transmission routes to model 1: (1) oral sex followed by anal sex (or vice versa) (model 2); (2) using saliva as a lubricant for penile-anal sex (model 3) and (3) oral sex followed by oral-anal sex (rimming) or vice versa (model 4). The next four models (models 5-8) used combinations of the three transmission routes.

RESULTS

The baseline model could only replicate infection at the single anatomical site and underestimated multisite infection. When we added the three transmission routes to the baseline model, oral sex, followed by anal sex or vice versa, could replicate the prevalence of multisite infection. The other two transmission routes alone or together could not replicate multisite infection without the inclusion of oral sex followed by anal sex or vice versa.

CONCLUSIONS

Our gonorrhoea model suggests sexual practices that involve oral followed by anal sex (or vice versa) may be important for explaining the high proportion of multisite infection.

Predicting the diagnosis of HIV and sexually transmitted infections among men who have sex with men using machine learning approaches

OBJECTIVES

We aimed to develop machine learning models and evaluate their performance in predicting HIV and sexually transmitted infections (STIs) diagnosis based on a cohort of Australian men who have sex with men (MSM).

METHODS

We collected clinical records of 21,273 Australian MSM during 2011-2017. We compared accuracies for predicting HIV and STIs (syphilis, gonorrhoea, chlamydia) diagnosis using four machine learning approaches against a multivariable logistic regression (MLR) model.

RESULTS

Machine learning approaches consistently outperformed MLR. Gradient boosting machine (GBM) achieved the highest area under the receiver operator characteristic curve for HIV (76.3%) and STIs (syphilis, 85.8%; gonorrhoea, 75.5%; chlamydia, 68.0%), followed by extreme gradient boosting (71.1%, 82.2%, 70.3%, 66.4%), random forest (72.0%, 81.9%, 67.2%, 64.3%), deep learning (75.8%, 81.0%, 67.5%, 65.4%) and MLR (69.8%, 80.1%, 67.2%, 63.2%). GBM models demonstrated the ten greatest predictors collectively explained 62.7-73.6% of variations in predicting HIV/STIs. STIs symptoms, past syphilis infection, age, time living in Australia, frequency of condom use with casual male sexual partners during receptive anal sex and the number of casual male sexual partners in the past 12 months were most commonly identified predictors.

CONCLUSIONS

Machine learning approaches are advantageous over multivariable logistic regression models in predicting HIV/STIs diagnosis.