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It is important that all men who have sex with men (MSM) accessing sexual healthcare are tested for Neisseria gonorrhoeae (GC) and Chlamydia trachomatis (CT) at all anatomical sites where they may be at risk of infection. In the United Kingdom, culture is considered the diagnostic gold standard for GC at extragenital sites owing to its high specificity, while nucleic acid amplification tests (NAATs) are preferred for CT. However, sometimes rectal CT testing is only offered to symptomatic patients and often testing for pharyngeal CT infection is not performed at all because of both technical and financial concerns.1
In this issue of STI Ota et al present the results of a study examining the performance of culture and NAATs for the detection of CT and GC in extragenital sites in a high-prevalence group of MSM.2 Worryingly, very low sensitivity data for both CT and GC culture in rectal sites (21% and 41.4% respectively) and pharyngeal sites (0% for both agents) are reported. While the authors stress that their culture facilities may be suboptimal they are probably representative of many clinical settings and this highlights the problems with using culture as a diagnostic test. This is particularly relevant when using culture to detect STIs in extragenital sites where the infectious agents are fastidious in nature, present in low numbers and may be masked by high levels of commensal bacteria. To date the highest reported sensitivity data for culture in the rectum are 27% (CT) and 86.4% (GC), and in the pharynx they are 44% (CT) and 41% (GC), so even with the best culture facilities available a significant number of infections will go undetected.3 4 An undiagnosed reservoir of CT and …
Competing interests: None.