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BACKGROUND: The Massachusetts Department of Public Health examined economic disparities in the incidence of infectious syphilis in Massachusetts by small-area analysis. There was a seven-fold increase in infectious syphilis incidence between 2001 and 2013 statewide. This analysis relies on methods used in previous studies of HIV/AIDS prevalence and poverty in Massachusetts.
METHODS: Using U.S. census tract socioeconomic data and population counts and Massachusetts syphilis data, the incidence of syphilis from 2001 to 2013 was analyzed with respect to the poverty level of census tracts in which patients resided. Geocoding was performed using ArcGIS. Data were stratified by age, sex, and race/ethnicity to study trends over time.
RESULTS: There were 4,472 cases of primary, secondary, and early latent syphilis reported 2001 - 2013. Five percent (233) were not geocoded because of homelessness, incarceration, missing street address or address of congregate living facility. Of the remaining 4,239 domiciled cases, 95% (4,239) were successfully geocoded. The incidence per 100,000 of syphilis among African Americans was 15.10, among Hispanics 10.92, and among white non-Hispanics 3.56. Other racial/ethnic groups had unstable rates due to a small number of cases. From 2001 to 2013, the overall incidence per 100,000 was 15.48 in census tracts where 40 - 100% of the population lived below the poverty level, 12.58 where 20-39% of the population lived below the poverty level, 8.38 where 10-19% of the population lived below the poverty level, 5.33 where 5-9% of the population lived below the poverty level, and 3.00 where 0-4% of the population lived below the poverty level. The highest incidence rates for each racial/ethnic group (black, Hispanic, and white), gender, and age group were in the poorest census tracts. Disparities in syphilis incidence by census tract poverty level were small in 2001. While syphilis incidence has increased in all census tract groups during this time period, the disparity between groups by poverty level has also increased over time. The largest disparities have occurred since 2010.
CONCLUSIONS: Greater socioeconomic disparities by area poverty level have been identified even as syphilis incidence has increased in all census tract groups over the past decade.