Introduction: Mycoplasma genitalium (MG) is increasingly seen as a clinically relevant sexually transmitted infection (STI), with a clinical spectrum similar to Chlamydia trachomatis (CT) and Neisseria gonorhoeae, including pelvic inflammatory disease and adverse reproductive outcomes. In the Netherlands, MG testing is not currently recommended for first-line STI screening despite a~4% background prevalence. Very little is known about co-infections with CT or NG as patients are usually only tested after negative CT/NG tests. We therefore studied the co-occurrence of MG and CT in both low- and high-prevalence populations.

Methods 1024 CT-positive participants from the Dutch general population (participants in the Chlamydia Screening Intervention-study) (60.3%; 462 ♀) and STI-clinic in South Limburg, the Netherlands (39.6%; 259 ♀) were retrospectively tested for MG. Men provided urine samples and women self-collected vaginal swabs. Samples were tested for human cells to ensure adequate sampling. CT/MG co-infections were investigated and correlated to symptoms. Statistical testing was performed using Chi-square test.

Results Of 1024 CT-positive patients, 5.5% had a co-infection with MG. CT/MG co-infections were present in 6.3% of the general population, compared to 4.2% of STI-clinic visitors. 3.9% of STI-clinic women had a CT/MG co-infection, compared to 7.4% in the general population. STI-clinic and general population men had a similar MG prevalence of 3.2% and 4.7%. Symptoms were reported by 37.3% of patients; 37.2% in single CT-infections and 39.3% in CT/MG co-infections.

Conclusion CT/MG co-infections are at least as common (5.5%), and in some populations more common (up to 7.4%), than in the general (CT-negative) population. As MG-testing is currently not routine practice in most clinics, these women go undiagnosed and receive inferior treatment, which likely contributes to current 30%–45% azithromycin resistance in MG. However, the higher prevalence of MG in the general population and the similar frequency of symptoms in both groups questions the clinical relevance of this pathogen.