US investigators have found a high incidence of recent HIV infection amongst men diagnosed with primary or secondary syphilis. In a study published in the February 1st edition of the Journal of Acquired Immune Deficiency Syndromes HIV incidence was 11% amongst gay men with early forms of syphilis. The investigators suggest “intensive and integrated HIV/STD testing, care and prevention services are needed for men diagnosed with syphilis.”
Since the late 1990s numerous outbreaks of syphilis have been recorded amongst gay men in industrialised countries. There are concerns that these outbreaks could have implications for the spread of HIV amongst gay men. This is because syphilis infection can be a marker of risky sexual behaviour and because syphilis can facilitate the transmission and acquisition of HIV.
Some research from the US has found a high incidence of HIV amongst gay men with syphilis. To gain a better understanding of the relationship between incident HIV infections and primary and secondary syphilis infection, investigators analysed data from men diagnosed with the sexually transmitted infection at sexual health clinics in Atlanta, Los Angeles and San Francisco between January 2004 – January 2006.
Blood samples used to diagnose syphilis were tested for HIV infection. Samples which were HIV-positive were then further analysed to see if the HIV infection was recent.
A total of 457 cases of syphilis were identified in the three cities, but the investigators restricted their analysis to the 357 men with primary or secondary syphilis. These men had a median age of 35 years and were ethnically diverse (37% white, 30% black and 25% Hispanic). Most of the men (85%) were gay.
Consistent with other research, the investigators found a high prevalence of HIV infection (45%) amongst men with primary and secondary syphilis.
This infection was well-established in most of the men, with 61% having a record of a positive HIV antibody test six or more or a history of antiretroviral therapy six months before their syphilis diagnosis.
But further blood tests showed that eleven men, ten of whom were gay, had evidence of recent HIV infection. The investigators calculated that HIV incidence amongst men with early syphilis was 10% per year for all men and 11% per year for gay men.
Further analysis showed that HIV incidence varied according to age. Amongst men with early syphilis aged under 30 incidence was 14% per year, 8% for men aged 30 – 39, and 5% for men aged 40 and above. Incidence also appeared to differ according to ethnicity, with an incidence of 14% per year amongst white men, 7% amongst black men and 6% amongst Hispanic men.
“In this population of consecutive men diagnosed with early syphilis in STD clinics in Atlanta, San Francisco, and Los Angeles, we found a high incidence of HIV infection during 2004 and 2005,” write the investigators.
The investigators work supports earlier research from the US that found that syphilis outbreaks were concentrated in gay men, many of whom are HIV-positive and were engaging in high-risk sexual behaviours.
“In these sexual networks, HIV-uninfected men acquiring syphilis are simultaneously at a high risk of HIV acquisition for multiple reasons”, suggest the investigators. They go on to explain “recent syphilis infection…facilitates HIV acquisition because syphilitic ulcers disrupt epithelial and mucosal barriers and local inflammation may lead to the recruitment of CD4 target cells to the site of ulceration.”
Furthermore, because these HIV-negative men are sexually active within networks that have a high prevalence of HIV-positive men “their probability of encountering an HIV-infected partner is increased.” Finally, HIV-positive men in these networks with syphilis are more likely to transmit HIV because their “viral load may be elevated in early syphilis infection.”
The investigators recommend that HIV-negative men diagnosed with syphilis should have follow-up appointments at sexual health clinics three and six months after their treatment for syphilis to verify that this treatment was successful and “for repeat HIV antibody testing, risk reduction education, and linkage to HIV care in the event of seroconversion.”
Buchacz K et al. HIV incidence among men diagnosed with early syphilis in Atlanta, San Francisco, and Los Angeles, 2004 – 2005. J Acquir Immune Defic Syndr 47: 234 – 240, 2008.