In 2019, investigators observed a 178-fold difference in syphilis incidence among individuals with HIV compared with those without HIV. These findings were based on the screening of 194,322 individuals undergoing care at a Veterans Health Administration facility and were published in Open Forum Infectious Diseases.

The investigators identified treponemal and nontreponemal tests, HIV status, and demographic data in VHA patients between 2009 and 2019. Syphilis testing rates and incident diagnoses defined by a laboratory algorithm were then stratified against HIV status.

Between 2009 and 2019, the rate of testing for syphilis declined; however, the percentage of tested individuals with a syphilis diagnosis remained stable at 0.9% in 2009 and 1.2% in 2019. For people with HIV, testing rates were higher and were found to have increased by 11% during this time period. In 2019, testing rates for people with HIV were 20 times those for HIV-negative individuals, for whom testing rates decreased by 16% over the study period. The percentages of tested individuals with a positive syphilis diagnosis in 2009 and 2019 were 4.1% and 6.1% for HIV-positive individuals and 0.6% and 0.7% for HIV-negative persons, respectively.


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In total, 2283 individuals were diagnosed with syphilis in 2019, 46% of whom were HIV positive. Over the 10-year period, the incidence of syphilis diagnoses increased 17% (from 30/100,000 in 2009 to 35/100,000 in 2019). The incidence of a syphilis diagnosis was 3381/100,000 for people with HIV and 19/100,000 for those without. Between the years of 2009 and 2019, the incidence of syphilis in the HIV-negative cohort remained stable while it increased 61% over the same period among the HIV-positive group. Across all racial groups, HIV was associated with higher incidences of syphilis diagnosis. Incidence by age, however, differed by HIV status to the point that in older people who represent the lowest-risk HIV-positive group, the incidence was higher than in younger people who represent the highest-risk non-HIV group. For individuals aged 18 to 24 years with HIV, the incidence of syphilis in 2019 was 14,414/100 000 compared with 48/100,000 for HIV-negative individuals of the same age.

This study has several limitations, including the lack of data on men having sex with men and the definition of incident syphilis relied on laboratory results and did not include patient-level clinical review. The sample comprised predominantly male individuals and is not generalizable to women, and the testing and diagnoses in this analysis may not be representative of individuals outside of the VHA.

According to the investigators, based on these data from the largest provider of HIV care in the United States, the incidence of syphilis diagnoses in people with HIV is far greater than in HIV-negative individuals. They believe the results are concerning because the incidence among people with HIV in 2019 was approximately 8 times greater than the often-cited peak incidence in the last century, which occurred during World War II. The researchers stress the need for national data that include information on HIV status and sexual orientation in order to verify these findings, inform potential syphilis screening indications and intervals among HIV-positive people, and guide future research.

Reference

Maier MM, Gylys-Colwell I, Lowy E, et al. Differences in syphilis incidence using a laboratory algorithm in people with and without HIV in an 11-year nationwide cohort study. Open Forum Infect Dis. 2021;8(2):ofab030. doi:https://doi.org/10.1093/ofid/ofab030