Results of a 25-year longitudinal analysis of the serologic incidence of syphilis in a cohort of HIV-infected patients with unrestricted access to care

Abstract

Background: The well-described biologic and epidemiologic associations of syphilis and HIV are particularly relevant to the military, as service members are young and at risk for sexually transmitted infections. We therefore used the results of serial serologic testing to determine the prevalence, incidence, and risk factors for incident syphilis in a cohort of HIV-infected Department of Defense beneficiaries.

Methods: Participants with a positive nontreponemal test at HIV diagnosis that was confirmed on treponemal testing were categorized as prevalent cases, and participants with an initial negative nontreponemal test who subsequently developed a confirmed positive nontreponemal test were categorized as incident cases.

Results: At HIV diagnosis, the prevalence of syphilis was 5.8% (n = 202). A total of 4239 participants contributed 27,192 person-years (PY) to the incidence analysis and 347 (8%) developed syphilis (rate, 1.3/100 PY; [1.1, 1.4]). Syphilis incidence was highest during the calendar years 2006 to 2009 (2.5/100 PY; [2.0, 2.9]). In multivariate analyses, younger age (per 10 year increase hazard ratio [HR], 0.8; [0.8-0.9]), male gender (HR, 5.6; [2.3-13.7]), non-European-American ethnicity (African-American HR, 3.2; [2.5-4.2]; Hispanic HR, 1.9; [1.2-3.0]), and history of hepatitis B (HR, 1.5; [1.2-1.9]) or gonorrhea (HR, 1.4; [1.1-1.8]) were associated with syphilis.

Conclusions: The significant burden of disease both at and after HIV diagnosis, observed in this cohort, suggests that the cost-effectiveness of extending syphilis screening to at-risk military members should be assessed. In addition, HIV-infected persons continue to acquire syphilis, emphasizing the continued importance of prevention for positive programs.

Figure 1

Flow diagram describing participant selection for the Incidence and Prevalence analyses

Figure 2A. Syphilis Testing Rates by calendar year

The solid and dotted lines represent the local linear robust fit smoothing line and the pointwise 95% confidence intervals respectively for the prevalence of syphilis at HIV diagnosis. The shaded bars represent testing rates by year.

Figure 2B. Syphilis Testing Rates at HIV Diagnosis by calendar year

The solid and dotted lines represent the local linear robust fit smoothing line and the pointwise 95% confidence intervals respectively for the prevalence of syphilis at HIV diagnosis. The shaded bars represent testing rates by year.

Figure 3. Prevalence of syphilis cases at the time of HIV diagnosis and by calendar year

The solid and dotted lines represent the local linear robust fit smoothing line and the pointwise 95% confidence intervals respectively for the prevalence of syphilis at HIV diagnosis. The dark shaded bars represent subjects with early disease.

Figure 4A. Incidence of syphilis after HIV diagnosis and by calendar year

The solid and dotted lines represent the local linear robust fit smoothing line and the pointwise 95% confidence intervals respectively for the incidence of syphilis after HIV diagnosis.

Figure 4B. Distribution of incident syphilis cases diagnosed with early disease by calendar year

The solid and dotted lines represent the local linear robust fit smoothing line and the pointwise 95% confidence intervals respectively for the incidence of early syphilis cases after HIV diagnosis.

Figure 4C

Incidence of syphilis cases after HIV diagnosis among African Americans and European Americans in the NHS