From 2000 through mid-2010, 15% of New York City men already diagnosed with syphilis were infected with HIV, according to results of a population-level analysis. Among men who have sex with men (MSM), more than 5% with syphilis had HIV infection within a year.
In New York City and other North American and European cities, men -- and predominantly MSM -- generally account for the lion's share of HIV and other sexually transmitted disease (STD) infections. Epidemiologic studies indicate that people with syphilis run a high risk of HIV infection. Researchers in the New York City Department of Health conducted this study to measure HIV incidence in men following a diagnosis of primary or secondary syphilis in order to identify high-risk groups who may benefit from HIV-blocking interventions such as preexposure prophylaxis (PrEP).
The investigators used an algorithm to match cases of syphilis and HIV reported in men in the NYC HIV/AIDS and STD surveillance registries. Matching involved 36 combinations of patient information, such as name, birth date and social security number. Among men diagnosed with syphilis from 2000 through June 2010, the researchers calculated HIV incidence. They used Cox proportional hazards models to identify risk factors for incident HIV infection.
From January 2000 through June 2010, the registries showed 6,053 men with syphilis, of whom 3,081 (51%) had an HIV diagnosis before January 2000. Another 167 men were diagnosed with HIV within 60 days of their syphilis diagnosis. To calculate HIV incidence, the researchers focused on the remaining 2,805 men with syphilis who did not have prior or concurrent HIV infection. Median age of these 2,805 men was 33 years (range 14 to 86), and approximately one-third were black, one-quarter white and one-quarter Hispanic. Two-thirds were MSM.
During an average follow-up time of 4.2 years, 423 of these 2,805 men with syphilis (15.1%) were diagnosed with HIV infection. Time to HIV diagnosis ranged from 60 days to 8.6 years (median 1.6 years). Annual HIV incidence measured 3.61% and did not vary greatly across major racial/ethnic groups. But HIV incidence was substantially higher in MSM (5.56%) than in men who have sex with women (1.20%) and other risk groups (0.46%). Men with a bacterial STD diagnosed after syphilis had a higher HIV incidence (7.89%) than men with only syphilis (2.89%) or those with a concurrent bacterial STD (3.44%).
Cox models identified three independent predictors of newly diagnosed HIV infection in men with syphilis: MSM compared with men who had other, unknown, or injection drug use risk of HIV (adjusted hazard ratio [aHR] 8.88, 95% confidence interval [CI] 5.20 to 15.18), secondary syphilis versus primary syphilis (aHR 1.37, 95% CI 1.10 to 1.72) and concurrent or subsequent STD versus only syphilis (aHR 2.03, 95% CI 1.65 to 2.50).
The authors say their findings "point to the need for more effective primary HIV prevention efforts among all men with P&S [primary and secondary] syphilis and especially for MSM and men with syphilis followed by other bacterial STD." Previous work determined that an HIV incidence of 2.4% -- more than 1% lower than the rate in this study -- means 41% of men HIV-negative at age 18 will be positive by age 40.
The NYC team proposes that clinicians and health authorities consider "promising HIV prevention strategies" such as PrEP and "existing effective interventions" such as frequent repeat HIV testing to stem the spread of HIV among men with syphilis.
Mark Mascolini is a freelance writer focused on HIV infection.