Objectives: We assessed the epidemiology of primary and secondary syphilis in the United States and estimated the percentages of cases occurring among men who have sex with men (MSM).
Methods: We reviewed US syphilis surveillance data from 1990 through 2003. We estimated the number of cases occurring among MSM by modeling changes in the ratio of syphilis cases among men to cases among women.
Results: During 1990 through 2000, the rate of primary and secondary syphilis decreased 90% overall, declining 90% among men and 89% among women. The overall rate increased 19% between 2000 and 2003, reflecting a 62% increase among men and a 53% decrease among women. In 2003, an estimated 62% of reported cases occurred among MSM.
Conclusions: Increasing syphilis cases among MSM account for most of the recent overall increase in rates and may be a harbinger of increasing rates of HIV infection among MSM. National efforts are under way to improve monitoring of syphilis trends, better understand factors associated with the observed increases, and improve efforts to prevent syphilis transmission.