Background: The Indianapolis MSA (District 5) has had a steady rise in syphilis for several years and comprises the largest share of morbidity in the state, reporting 133 P&S cases and 119 early latent cases in 2015. A review of literature yielded minimal publications that assessed syphilis reinfection rates by year of diagnosis. Studies ranged from a reinfection rate of 5.9% within two years (California 2002-2006) to 20% (Baltimore 2010-2011).
Methods: Extraction of reported morbidity for primary, secondary, and early latent syphilis in District 5 from 2008-2015 came from Indiana’s STD reporting database, SWIMSS. Individuals were included in 5-year cohorts from the entrance of the patient into the dataset to allow enough time for reinfection to occur while minimizing bias. SAS analysis, including Chi-squared and logistic regression, was used to examine differences in age, race, sex, orientation, HIV status, and syphilis staging diagnosis.
Results: Of the 1,362 reported cases of early syphilis, the overall reinfection rate for 2008-2015 was 15.27%. Reinfection rates have increased over time as 2015 alone had a 31% reinfection rate. Of the 208 total patients with repeat syphilis infections, 78% experienced 2 infections, 1.98% had 3 infections, and 1.40% had ≥ 4 infections. In 2015, significant risks for reinfection included MSM orientation (76.2 vs. 93.7%, p=.0019) and HIV+ status (37.0 vs 79.5%, p<.0001). Logistic regression showed that the risk of reinfection was only significant in the HIV+ patients (OR=5.192 [2.526, 10.671]).
Conclusions: In our analysis, 15.27% of patients experienced more than one syphilis infection. Those with HIV were more likely to have a repeat infection, and the occurrence of repeat infections seems to be increasing over time. Analysis and prevention of repeat syphilis infections is a challenging but important step for enhanced public health efforts to address the groups at highest risk of reinfection.