Changes in demographics and risk behaviors of persons with early syphilis depending on epidemic phase

BACKGROUND: Syphilis incidence has been rising in the United States since 2000. Shifts in syphilis epidemic phases may be associated with changes between or within high-risk populations. OBJECTIVES/GOAL: To determine whether shifts in syphilis epidemic phases are associated with changes between or within high-risk populations. STUDY DESIGN: Using surveillance data collected from Baltimore, MD, 1994-2004, we retrospectively defined epidemic phases and compared epidemiologic profiles of syphilis cases infected during epidemic phase. RESULTS: We defined 3 epidemic phases. The shift between hyperendemic and decline phases was not associated with demographic or behavioral changes among persons with syphilis. Compared to the decline phase, men infected with syphilis during the growth phase were 5 times [odds ratio (OR) 5.32 P <0.001] more likely to report having had sex with men (MSM) or women. Men and women infected during the growth phase were less likely to be >25 years of age (men: OR 0.60, P <0.001; women: OR 0.60, P <0.001), and more likely to be non-African American (men: OR 6.21 P <0.001; women: OR 7.76, P <0.001). Demographic trends persisted when we restricted the analysis to MSM and then restricted to young (age ≤25 years), non-IDU (injecting drug-using) women. Additionally, young, non-IDU women infected in the growth phase were significantly more likely to report ≥5 recent sex partners (OR 4.30, P <0.01) than those in the decline phase. CONCLUSIONS: We verified that the shift from a decline to growth phase in Baltimore was mostly because of increases in morbidity among non-African American MSM and young, non-IDU women with ≥5 recent sex workers. Although syphilis control activities have been targeted towards these groups, our analysis underscores the need for real-time investigation of potential tipping points to ensure interventions are properly focused at the beginning of any potential growth phase.