Epidemiology
Epidemiologic studies demonstrate that history of an STD, including syphilis, is associated with an increased risk of HIV disease among both gay men (7,9) and heterosexuals (8) because sexual behaviors that increase the risk of acquiring STDs also increase the risk of acquiring HIV. Furthermore, genital ulcerations and inflammation caused by STDs are implicated as cofactors for acquiring or transmitting HIV infection.(9-11) Recent data suggest that when they already have other STDs, individuals are 3 to 5 times more likely to acquire HIV if exposed to the virus through sexual contact.(10)
In U.S. areas reporting high rates of syphilis infection in the early 1980s, the percentage of early syphilis cases occurring among gay and bisexual men decreased from 50% to 70% in the late 1970s to 5% to 15% in 1990.(53) These data were thought to reflect changes in sexual practices that reduced the risk of HIV infection among gay and other men who have sex with men (MSM) and suggested that education efforts encouraging safer-sex practices were effective. During the 1990s, the geographic distribution of heterosexual HIV transmission closely paralleled that of syphilis. Most of the health districts with the highest rates of syphilis in 1995 were concentrated in the southern United States, where the HIV prevalence among childbearing women also was highest. Therefore, increases in the incidence of STDs in any population may presage future increases in HIV, illustrating the importance of STD diagnosis and treatment as an HIV preventive strategy.
Despite significant decreases in cases of syphilis in the United States in the 1990s, as well as the CDC's initiative to eliminate the disease domestically by 2005, syphilis incidence has risen dramatically since 2000, particularly among MSM.(3,54-60) (See the CDC's Syphilis Surveillance Project Annual Report for a detailed epidemiologic update.) In 2004, 7,980 cases of primary and secondary syphilis were reported nationally, representing an 11.2% increase over 2003 and a 33% increase over the previous decade's nadir of 5,979 cases, reported in 2000.(61) A number of states have experienced particularly large recent increases in syphilis, concentrated among MSM. In 2005 in California, for instance, 1,489 cases of primary and secondary syphilis were reported, representing an increase of more than 700% from 1999. Of the 2005 cases, 79% were MSM and of those, 61% were HIV positive by self-report, and a majority (60%) reported multiple anonymous sex partners.(62) Recently, the Syphilis Elimination Effort has been launched as a national initiative to bring together health care providers, policy makers, community leaders, and state and local public health agencies to reduce syphilis rates in the United States.
Suggested causes of this resurgence in syphilis among MSM include increases in the number of anonymous sex partners, decreases in condom use, use of the Internet for meeting sex partners, and more widespread use of methamphetamine and proerectile agents, among other drugs.(4,63-67) Oral sex has been implicated in 14% of syphilis infections in a large U.S. city.(68) Moreover, the indirect contribution of antiretroviral treatment (ART) to higher syphilis transmission rates among those infected with HIV has been well described.(69) These epidemiologic trends underscore the importance of clinicians' awareness of key behavioral risk factors, their consideration of syphilis in the differential diagnosis of similarly presenting disorders, and their familiarity with current recommendations regarding risk assessment, screening, and clinical management of syphilis.
Limited epidemiologic data suggest that neurosyphilis remains an uncommon infection in HIV-infected patients. A retrospective surveillance investigation of neurosyphilis trends in San Francisco from 1985 through 1992 found no evidence of increasing rates of neurosyphilis during the study interval.(70) Reports of symptomatic neurologic involvement totaled 2 to 5 cases per year. No cases of early neurosyphilis were identified in HIV-uninfected patients. More recent surveillance has confirmed a consistently low incidence of neurosyphilis in San Francisco, found in 2.7% (33/1,232) of all syphilis cases (all stages) in 2002 to 2003.(71)
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