Evaluation of ligase chain reaction for the non-cultural detection of rectal and pharyngeal gonorrhoea in men who have sex with men

Objectives: To compare a nucleic acid amplification test ( ligase chain reaction) with culture for detecting rectal and pharyngeal gonorrhoea in men who have sex with men ( MSM). Methods: Duplicate rectal and throat swabs from MSM attending a genitourinary medicine clinic were collected for culture on modified New York City medium and detection of gonococcal nucleic acid by the Abbott ligase chain reaction ( LCR) utilising probes based on opa 1 gene sequences. LCR positive culture negative specimens were tested by a second LCR utilising probes based on pilin gene sequences. Patients with rectal and/ or pharyngeal cultures yielding Gram negative diplococci confirmed as Neisseria gonorrhoeae by biochemical and immunological methods were diagnosed with rectal and/ or pharyngeal gonorrhoea. The criteria for diagnosing rectal and pharyngeal infection by LCR included a positive opa LCR with a positive culture from the same site or, in the case of a negative culture, a positive opa LCR and a positive pilin LCR. Results: Duplicate rectal samples were obtained from 227 MSM. The results of LCR and culture were concordant in 219 samples ( 96.5%). The prevalence of rectal gonorrhoea by LCR and culture was 7.0% ( 16/ 227) and 4.0% ( 9/ 227), respectively. Duplicate throat samples were obtained from 251 MSM. The results of LCR and culture were concordant in 230 ( 91.6%) cases. The prevalence of pharyngeal gonorrhoea by LCR and culture was 12.7% ( 32/ 251) and 6.0% ( 15/ 251), respectively. The specificity of LCR was 99.5% ( 210/ 211) for rectal and 98.2% ( 215/ 219) for pharyngeal specimens. Conclusions: The high prevalence and asymptomatic nature of pharyngeal and rectal gonococcal infection suggests that routine screening for infection at these sites by a nucleic acid amplification test method such as LCR should be considered as part of the overall strategy to control gonorrhoea in MSM.