Prevalence, incidence and predictors of anal Chlamydia trachomatis, anal Neisseria gonorrhoeae and syphilis among older gay and bisexual men in the longitudinal Study for the Prevention of Anal Cancer (SPANC)

Abstract

Objectives: Sexually transmitted infection (STI) notifications are increasing among older individuals. Many older gay and bisexual men (GBM) are sexually active and have multiple partners. We aimed to investigate the prevalence, incidence and predictors of anal chlamydia, anal gonorrhoea and syphilis in older GBM.

Methods: The Study for the Prevention of Anal Cancer (SPANC) was a prospective cohort study of HPV infections and related anal lesions among community-recruited GBM age ≥ 35 years in Sydney, Australia. At baseline and subsequent annual visits, recent STI diagnoses were collected via questionnaire ('interval diagnoses') and STI testing occurred ('study visit diagnoses'). Baseline STI prevalence was calculated using study visit diagnoses. Incidence of anal chlamydia and gonorrhoea was calculated using interval and study visit diagnoses. Syphilis incidence was calculated using interval diagnoses. Univariate and multivariate analysis using Cox proportional hazards were undertaken to investigate the association between risk factors and incident STI.

Results: Among 617 GBM, the median age was 49 years (range 35-79) and 35.8% (n=221) were HIV-positive. At baseline, STI prevalence was: anal chlamydia 2.3% (n=14); anal gonorrhoea 0.5% (n=3) and syphilis 1.0% (n=6). During 1428 person-years of follow-up (PYFU), the incidence (per 100 PYFU) of anal chlamydia, anal gonorrhoea and syphilis was 10.40 (95% CI 8.82 to 12.25), 9.11 (95% CI 7.64 to 10.85) and 5.47 (95% CI 4.38 to 6.84), respectively. In multivariate analysis, HIV-positivity, higher number of recent condomless receptive anal intercourse partners and baseline methamphetamine use were associated with each STI. Sex with 'fuck-buddies' was associated with anal chlamydia and gonorrhoea. Age was not associated with any STI.

Discussion: There was a high incidence of STI among SPANC participants. Age should not be used as a proxy for sexual risk and older GBM require a detailed sexual behaviour and recreational drug use history. Interventions that specifically target STI risk among older GBM should be considered.

Keywords: chlamydia trachomatis; gay men; neisseria gonorrhoea; sexual behaviour; syphilis.