Achilleas Tsoumanis

This thesis explores the impact of STI screening and treatment strategies on gonorrhea, chlamydia, and antimicrobial resistance among MSM in Belgium by integrating systematic review, empirical data analysis, and network modelling. It begins with a review of existing evidence on the effects of screening, identifying key gaps that motivate the need for improved modelling. A mathematical model is then developed to assess the impact of screening coverage on gonorrhoea prevalence. Limitations in key behavioural parameters are identified, such as partnership duration and homophily. These therefore necessitate empirical estimation. Using primary data, these parameters are refined to enhance model accuracy. The improved model is then applied to evaluate the effects of different gonorrhoea treatment strategies on antimicrobial-resistant gonorrhoea and chlamydia, as well as the impact of different screening strategies on STI prevalence. The findings highlight the importance of optimizing screening and treatment policies to balance infection control with resistance prevention, providing valuable insights for public health interventions.

Background: Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are two of the most common bacterial sexually transmitted infections (STIs) among men who have sex with men (MSM). Screening for CT and NG has been promoted as an intervention to reduce the prevalence of these STIs. We aimed to evaluate the effect of different screening intensities on the prevalence of CT, NG and the emergence of azithromycin-resistant NG (AR-NG) in an MSM population. Methods: We developed a network-based model for CT and NG transmission among MSM in Belgium to estimate the prevalence of CT, NG and AR-NG in the population. The model simulates transmission of CT/NG among three anatomical sites in a population of 10 000 MSM, divided into high-activity and low-activity groups, over 10 years. The effect of different screening frequencies and coverage was evaluated in terms of CT, NG and AR-NG prevalence. Results: Gonorrhoea prevalence ranged between 12% and 16% in scenarios screening 0–80% of the population. Screening among the low-activity MSM (LA-MSM) group had little effect on NG prevalence but increased the risk of AR-NG. Infrequent screening (less than every 180 days) with high coverage (over 40%) resulted in the highest risk for the spread of AR-NG in the population. Screening up to 40% of low-activity (HA-MSM) every 90 days and up to 20% of LA-MSM reduced NG prevalence to 14% without selecting for AMR. Screening coverage and frequency had little impact on CT prevalence in all scenarios. Conclusions: Our model suggests that NG/CT screening has a modest effect in controlling the prevalence of these infections in the MSM population in Belgium. Screening efforts should move away from LA-MSM. Screening alone would not be sufficient to control the CT/NG epidemic, and future models should incorporate the impact of additional interventions such as vaccination and doxycycline post-exposure prophylaxis.

Background: Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) are 2 of the most common bacterial sexually transmitted infections. The prevalence of azithromycin resistance in NG (AR-NG) has increased from 1% to 47.9% in the past 10 years among men who have sex with men (MSM) in Belgium. Dual therapy with ceftriaxone and azithromycin was until recently the standard-of-care in Belgium. Our objective was to reproduce the azithromycin-resistance epidemic among MSM in Belgium using dual therapy and to evaluate the counterfactual scenario of using ceftriaxone monotherapy on the emergence of AR-NG. Methods: We developed a network-based model for CT and NG transmission among MSM in Belgium to estimate the prevalence of CT, NG, and AR-NG in the population. The model simulates transmission of NG among 3 anatomical sites in a population of 10 000 MSM over 10 years. The effect of different treatment strategies was evaluated in terms of CT, NG, and AR-NG prevalence as well as antibiotic consumption. Results: Our model captured adequately well the observed azithromycin-resistance epidemic over a 10-year period in Belgium, with AR-NG increasing from 0% to 44%. Antibiotic consumption, and prevalences of NG and AR-NG decreased when ceftriaxone monotherapy was used against NG, while CT prevalence increased, compared to dual therapy. In the ceftriaxone monotherapy scenario, the prevalence of AR-NG was approximately half of that in the dual-therapy scenario (23%). Conclusions: Switching from dual to monotherapy was associated with a halving of the prevalence of AR-NG. These results provide further evidence to favor mono- over dual therapy for the treatment of gonorrhea.

Background: Clade Ib, a new strain of the Clade I monkeypox virus, emerged in Eastern Democratic Republic of the Congo, sparking an international outbreak. Comprehensive studies are needed to assess its transmission dynamics and clinical presentation. Methods: We conducted a prospective observational cohort study at Kamituga General Hospital in South Kivu, DRC, between May 2 and October 9, 2024. Sociodemographic, exposure and clinical data were collected from mpox suspected cases. Cases confirmed by Xpert® Mpox PCR were presumed Clade Ib infections (awaiting Clade confirmation) and followed through hospitalization and on days 29 and 59 post-diagnosis to assess clinical progression and outcomes. Findings: Of 511 included suspected cases, 431 (84%) tested PCR positive; with 205 being women (47%). Age distribution was bimodal, with 279 (65%) individuals aged 15-34 years, and 63 (15%) children under five. Most cases (59%) reported contact with a suspected or confirmed mpox case; among adults, this was primarily a spouse, colleague or sexual partner, while for children, the primary contacts were parents or siblings. Comorbidities were rare (4%), including six (1%) HIV infections. Prodromal symptoms were present in 346 (88%) patients, active skin lesions in 414 (96%), mucosal lesions in 338 (82%), and lymphadenopathy in 295 (71%). In adults, lesions were more concentrated in the genital area, with 90% of adults presenting lesions in this region. In contrast, only 39% of children had genital lesions, with lesions more frequently found elsewhere on the body. Among 427 hospitalized patients, two deaths (0·5%) occurred. Among 315 patients with detailed hospital follow-up, complications were primarily genito-urinary (55%) or cutaneous (40%). Four of six pregnant women with recorded outcome (67%) had adverse pregnancy outcomes. Significant sequelae at days 29 and 59 were rare. Interpretation: Clade Ib MPXV infections presented differently from previously reported Clade Ia and Clade IIb infections. In adults, the disease primarily affected the genito-urinary system, compatible with sexual transmission, while children mostly manifested extragenital lesions. Funding: European & Developing Countries Clinical Trials Partnership (EDCTP2 and EDCTP3); Belgian Directorate-General Development Cooperation and Humanitarian Aid; Research Foundation – Flanders

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.

Mathematical modelling is widely used for describing infection transmission and evaluating interventions. The lack of reliable social parameters in the literature has been mentioned by many modelling 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 literature. Our study addresses this lack of information by providing a method to estimate crucial parameters for network specification.

Introduction Autistic individuals identify with a wider range of sexual orientations than non-autistic individuals, including higher rates of bisexual orientation in autistic men. Gay, bisexual and other men who have sex with men are at greater risk for HIV. Prevalence data of autistic traits in people living with HIV or using Pre-Exposure Prophylaxis (PrEP) for HIV are lacking so far. Such data, combined with insights in barriers and facilitators for safer sex in autistic people living with HIV or using PrEP, are a first step to improve health support for autistic people in HIV clinics. This support is crucial since autistic individuals have worse physical and mental health outcomes. The objective of this research is to determine the prevalence of autistic traits within the group of people living with HIV or using PrEP in Belgium and to describe specific facilitators and barriers for sexual safer behaviour in people living with HIV and PrEP users with autistic traits. Methods and analysis The research is a cross-sectional, observational and multicentre study with recruitment of individual participants. The research consists of two phases. In phase 1, adults coming for HIV/AIDS care or HIV PrEP in participating Belgian HIV Reference Centres will be invited to fill in the validated Autism Spectrum Quotient questionnaire. In phase 2, participants with a score above the predefined cut-off for autistic traits (>26), who agreed to be informed about this score, will be invited to complete an additional survey, inquiring facilitators and barriers for sexual safer behaviour. Ethics and dissemination of results Institutional Review Board Institute of Tropical Medicine Antwerp, 25 July 2022, REF 1601/22 and University Hospital of Antwerp, 12 September 2022, Project ID 3679: BUN B3002022000111. Study results will be published in peer-reviewed journals and presented to Belgian HIV Reference Centres and at conferences.

Thibaut Vanbaelen, Achilleas Tsoumanis, Chris Kenyon; Total antimicrobial consumption in doxyPEP cohorts depends on the intensity of screening for bacterial sex

No randomized controlled trial (RCT) has compared the impact on the resistome of ceftriaxone (CRO) plus azithromycin (AZM) vs CRO for the treatment of Neisseria gonorrhoea (NG). This was an open-label, single-center, RCT comparing the effect on the resistome of CRO plus AZM vs CRO for the treatment of NG. Men who have sex with men (MSM) with genital, anorectal, or pharyngeal NG infection were randomized into the CRO/AZM and CRO arms. Oral rinse and anorectal samples were taken for culture and resistome profiling at 2 visits (baseline and day 14). The primary outcome was the ratio of mean macrolide resistance determinants in anorectal samples from day 14 between arms. Twenty individuals were randomized into the CRO/AZM arm and 22 into the CRO arm. We found no significant difference in the mean macrolide resistance determinants in the day 14 anorectal samples between arms (ratio, 1.05; 95% CI, 0.55–1.83; P = .102). The prevalence of baseline macrolide resistance was high (CRO/AZM arm = 95.00%; CRO arm = 90.91%). We could not demonstrate a significant effect of dual CRO/AZM therapy on the resistome compared with CRO alone, likely due to a high baseline resistance to AZM. Interventions to prevent the emergence of antimicrobial resistance in MSM are needed.