Introduction Although routine diagnostic methods for detection of Chlamydia trachomatis (CT) are based on Nucleic Acid Amplification Tests (NAAT) the detection of antibodies can also be used as an additional tool, especially for surveillance. People with a CT infection develop serum IgG and IgA, which are a marker for past infection and in women are correlated with infertility. Although seroprevalence of CT has been well studied in women, little is known about the seroprevalence of CT in men, especially in the high risk group men who have sex with men (MSM). The aim of this study is to assess the seroprevalence of CT in MSM and the development of seroconversion over time.
Methods A seroprevalence study was conducted in 291 MSM visiting the STI clinic of the Public Health Service South Limburg, the Netherlands, at least twice between January 2011 and December 2013. Sera from the last consultation (T2) were tested for the presence of IgG and IgA (Medac, Germany). Individuals with positive serology at T2 were additionally tested one year before (T1) to determine seroconversion. Prevalence data were calculated from the number of IgG and IgA positive sera at T2 and incidence data were calculated from the seroconversion rates between T1 and T2.
Results Thirty-one percent (n=91/291) of MSM was NAAT CT positive in the study period.
In 98% (286/291) MSM sera were available for testing. In total, 32% of MSM (91/286) were IgG positive and 17% were IgA positive (48/286), of which 44 were positive for both. The overall prevalence was 33% based on the presence of IgG and/or IgA antibodies (n=95). Seroconversion rate between T1 and T2 showed that 3,8% (n=11) seroconverted for IgG and 4,5% (n=13) for IgA, of which 1.7% (n=5) seroconverted for both. The overall incidence rate was 6,6% (n=19) based on seroconversion of IgG and/or IgA.
Conclusion This study showed that one third of MSM visiting an STI clinic were seropositive for CT. The incidence rate was about 6%. Association of CT seropositivity with sexual behaviour determinants and actual CT positivity will be further studied.
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