Recent Increase in Early Syphilis Among Heterosexuals in Philadelphia, 2006-2009

Background: In Philadelphia, from 2006-2008, reported early syphilis cases remained relatively stable.  Approximately 163 cases were reported every 6 months with most being among men who have sex with men (MSM), which has been the trend in Philadelphia since 2002. Between January and June, 2009, reported early syphilis cases increased substantially (225 cases).

Objectives: To assess demographic and geo-spatial trends in early syphilis in Philadelphia from 2006-2009.

Methods: Counts of early syphilis cases in the first 6 months of 2009 were compared to the average of 6 months periods in 2006-08. Variables of interest included gender, age, race/ethnicity, and MSM status. ZIP code level geo-mapping of residence was utilized.

Results: In the first 6 months of 2009, reported early syphilis increased by 37.9% (+62 cases) compared to the average 6 month-case reports from the preceding years. While reported cases among MSM increased (14.6% - +13 cases), a more notable increase occurred among women (52.1% - +12 cases) and heterosexual males (88.2% - +30 cases). In the first 6 months of 2009, the median age of early syphilis cases declined from 34 years to 30 years. Female cases had the largest decline in median age from 32.5 years to 25 years. Compared to the historical average, the proportion of cases identifying as Black increased (65.6% vs. 75.1%). Geo-mapping showed several areas of interest, but none were consistent over time. Whereas early syphilis cases among heterosexual men and women increased in 2009, reported cases of congenital syphilis increased in 2007.

Conclusions: In addition to the on-going MSM outbreak, there appears to be a new outbreak of early syphilis infection among heterosexuals.

Implications for Programs, Policy, and/or Research: The changing demographics of the syphilis outbreak in Philadelphia requires adjustments to syphilis prevention, provider education and screening priorities, which have focused on MSM in recent years.