Trends in Chlamydia trachomatis IgG seroprevalence in the general population of the Netherlands over 20 years.

OBJECTIVES: To report sex and age-specific Chlamydia trachomatis (Ct) seroprevalence estimates in the general population of the Netherlands between 1996 and 2017 and identify risk factors associated with Ct seropositivity. METHODS: Participants (n=5158, aged 15-59 years) were included from three independent nationwide population-based serosurveillance studies in 1996, 2007 and 2017. Participants completed a questionnaire on demographics and sexual behaviour. Serum antibodies were analysed using Medac Ct IgG ELISA test. Census weights were assigned to achieve seroprevalence estimates representative of the general Dutch population. Weighted seroprevalence estimates were stratified by gender, age and birth cohort. Trends and risk factors in men and women were identified using multivariable logistic regression. RESULTS: Weighted overall Ct seroprevalence was 10.5% (95% CI: 9.2% to 12.0%) in women and 5.8% (95% CI: 4.7% to 7.0%) in men. Among women <25 years, there was a non-significant increase in seroprevalence from 5.9% (95% CI 3.7% to 9.2%) in 1996, to 7.6% (95% CI 5.1% to 11.1%) in 2007 and 8.8% (95% CI 5.5% to 13.9%) in 2017. Among women ≥25 years, the seroprevalence significantly decreased from 15.6% (95% CI: 12.2% to 19.7%) in 1996 to 9.5% (95% CI: 7.2% to 12.4%) in 2007 but did not further drop (11.2% (95% CI 8.1% to 15.3%) in 2017). In men, we did not observe trends between study rounds. In both men and women, having a non-Western migration background was a risk factor for seropositivity. In women, having had a prior sexually transmitted infection and ≥2 recent sex partners were risk factors for seropositivity as well. CONCLUSIONS: We have not found evidence for a decrease in population seroprevalence in those under 25 years old despite decades of intensified testing-and-treatment efforts in the Netherlands. This suggests further monitoring of Ct burden in the general population is needed. If serum banks are used for this, specifically individuals <25 years old and with diverse migration backgrounds should be included.

Sexual risk behaviour trajectories among MSM at risk for HIV in Amsterdam, the Netherlands.

OBJECTIVE: Sexual risk behaviour changes during a person's life course. Insights in sexual risk behaviour trajectories of MSM may provide starting points for the timing of HIV prevention methods. We aimed to study longitudinal trajectories of sexual risk behaviour predictive of HIV acquisition from sexual debut onwards. DESIGN: A longitudinal study among 815 HIV-negative participants of the Amsterdam Cohort Studies (ACS) who completed extensive questionnaires about their sexual behaviour every 6 months between 2007 and 2017. METHODS: A comprehensive behavioural risk score predictive of HIV seroconversion was developed. On the basis of this risk score, linear trajectories of sexual risk behaviour and MSM group membership were estimated using latent class growth mixture modelling. Associations between longitudinal trajectories and demographic and psychosocial factors were examined. RESULTS: Three trajectories of sexual risk behaviour were identified, which were labelled Low risk (90.3% of the sample), Falling high risk (6.5%) and Rising high risk (3.3%). MSM following the Falling high risk (20.5%) and Rising high risk (25.0%) trajectories were more likely to acquire HIV during follow-up. The Falling high risk trajectory was associated with younger age at sexual debut, fewer steady partnerships and high percentages of substance use. The Rising high-risk trajectory was associated with increasing percentages of substance use over time. CONCLUSION: MSM follow different trajectories of changing sexual risk behaviour over time. Early identification of MSM following a trajectory of falling or rising high-risk behaviour and adequate timing of individual-based preventive interventions may reduce HIV transmission.

Reinfection by untreated partners of people treated for Chlamydia trachomatis and Neisseria gonorrhoeae: mathematical modelling study.

OBJECTIVES: Reinfection after treatment for Chlamydia trachomatis or Neisseria gonorrhoeae reduces the effect of control interventions. We explored the impact of delays in treatment of current partners on the expected probability of reinfection of index cases using a mathematical model. METHODS: We used previously reported parameter distributions to calculate the probability that index cases would be reinfected by their untreated partners. We then assumed different delays between index case and partner treatment to calculate the probabilities of reinfection. RESULTS: In the absence of partner treatment, the medians of the expected reinfection probabilities are 19.4% (IQR 9.2-31.6%) for C trachomatis and 12.5% (IQR 5.6-22.2%) for N gonorrhoeae. If all current partners receive treatment 3 days after the index case, the expected reinfection probabilities are 4.2% (IQR 2.1-6.9%) for C trachomatis and 5.5% (IQR 2.6-9.5%) for N gonorrhoeae. CONCLUSIONS: Quicker partner referral and treatment can substantially reduce reinfection rates for C trachomatis and N gonorrhoeae by untreated partners. The formula we used to calculate reinfection rates can be used to inform the design of randomised controlled trials of novel partner notification technologies like accelerated partner therapy.

Insights into the timing of repeated testing after treatment for Chlamydia trachomatis: data and modelling study.

OBJECTIVES: The objective of this study was to determine the optimal time interval for a repeated Chlamydia trachomatis (chlamydia) test. METHODS: The authors used claims data for US women aged 15-25 years who were enrolled in commercial health insurance plans in the MarketScan database between 2002 and 2006. The authors determined the numbers of initial positive and negative tests that were followed by a repeated test and the positivity of repeated tests. The authors used a dynamic transmission pair model that reflects the partnership formation and separation processes in 15-25 year olds to determine the time course of repeated infections in women under different levels of notifying the current partner. The authors then explored the additional impact of repeated testing uptake on reducing chlamydia prevalence. RESULTS: 40% (4949/12 413) of positive tests were followed by a repeated test compared with 22% (89 119/402 659) of negative tests at any time. Positivity of repeated tests followed by an initial positive test was high: 15% (736) after a positive test versus 3% (2886) after a negative test. The transmission model showed a peak in repeated infections between 2 and 5 months after treatment. For a chlamydia testing uptake of 10% per year, the additional impact of repeated testing on reducing chlamydia population prevalence was modest. CONCLUSIONS: The mathematical model predictions support the recommended interval for repeat chlamydia testing. This study provides information that can be used to design randomised controlled trials to determine more effective interventions to prevent chlamydial reinfection.