Objectives Numbers of newly diagnosed HIV infections among men who have sex with men (MSM) in Germany increased after the year 2000. We sought to explore trends in STI co-infections around the time of HIV seroconversion in patients from the German HIV-1 seroconverter cohort from 1996–2007.

Methods MSM from the cohort were included for secondary analysis, if seroconversion occurred between 1996 and 2007 and if a blood sample taken within 2 y after HIV infection was available for further testing. Samples were tested for antibodies against Treponema pallidum and HSV-2. A classification system was developed to assign the chronology of syphilis and HIV-1 infection.

Results Data of 1052 MSM were eligible for analysis. Overall seroprevalence of syphilis markers was 26%, increasing from 10% (1996–1999) to 35% (2005). Among HIV seroconverters with positive syphilis antibodies, 32% (n=88) were rated as having had coincident infections with HIV and syphilis. Coincident syphilis infection at HIV diagnosis increased substantially (p<0.001) from 2.3% in 2000 to 16.9% in 2003; and thereafter declined to 4.3% in 2007. Mean HSV-2 antibody prevalence was 40.5%, mean anti-HSV-2 IgM prevalence was 11.2%, with no significant change over time.

Discussion We found a stable prevalence of HSV-2 infection and increasing prevalence of syphilis infection around the time of HIV acquisition among MSM in Germany. Time course and rate of co-infections suggest that a re-emerging syphilis co-epidemic among MSM after 2000 could have contributed to an increase of HIV incidence by enhancing HIV transmission probability.