Incidence and Duration of Pharyngeal Chlamydia Among a Cohort of Men Who Have Sex With Men
Christine M. Khosropour, Olusegun O. Soge, Matthew R. Golden, James P. Hughes, Lindley A. Barbee
Abstract
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.