Background:
Public health data from case-reports are used to monitor trends in the disease incidence to identify outbreaks, target and evaluate public health responses. Recently behavioral surveillance activities have been added to public health programs to inform disease control efforts. Understanding the complex relationship between disease and behavior could help predict changes in the epidemiology of diseases allowing for earlier intervention and focused prevention efforts.

Objective:
Describe trends in syphilis and sexual risk behavior.

Method:
We reviewed syphilis surveillance data from 1996 to 2005 and compared trends in disease incidence with population-based data on sexual risk behavior during the same period.

Result:
The rate of new syphilis infections in men who have sex with men (MSM) began increasing in the 3rd quarter of 1999, peaked in the 2nd quarter of 2003, leveled and then began to decline in 1st quarter 2005. The mean number of sex partners in the prior 2 months reported by MSM visiting the municipal STD clinic increased from 4.3 in 1996 to 6.1 in 2002 then declined to 5.7 in 2005. Rates of any unprotected anal sex in MSM in the prior 6 months reported by gay men in serial monthly street-intercept surveys increased from 22% in 1996 to 38% in 2001 and declined or leveled off to 35% in 2004.

Conclusion:
Between 1996 and 2005 there were significant and substantial increases in syphilis and sexual risk behavior followed by declines. An ecologic analysis precludes determining if an association between syphilis and sexual behavior exists; however, it is reasonable to hypothesize that the trends may be linked.

Implications:
Sexually transmitted disease control efforts should continue to monitor and attempt to reduce sexual risk behavior in populations at risk for increased disease transmission.