Background Sexually transmitted proctitis occurs among persons who participate in receptive anal intercourse and is a risk factor for HIV acquisition. N. gonorrhoeae, C. trachomatis(including LGV), T. pallidum, and Herpes Simplex Virus (HSV) are the most common pathogens identified. The distribution of microbiologic aetiology of proctitis has implications for empiric treatment guidelines. Methods: We describe the microbiologic aetiology of clinical proctitis among men who have sex with men seen at the municipal STD clinic in San Francisco. N. gonorrhoeaeand C. trachomatiswere tested using a nucleic acid amplification assay, HSV was tested using polymerase chain reaction, and T. pallidum was tested using a non-treponemal antibody test, with T. pallidum particle agglutination confirmation. Results: Between January 1, 2004 and December 31, 2012, there were 1271 men diagnosed with clinical proctitis at the clinic. The number of cases of proctitis diagnosed annually did not increase over this interval, despite increasing rates of rectal gonorrhoea and Chlamydia. Overall, 820 (65%) of the cases had no microbiologic aetiology identified and nearly half were among HIV-infected men. Two-hundred sixty-three (21%) had gonorrhoea, 205 (16%) had Chlamydia, 53 (4.2%) had both gonorrhoea and Chlamydia, 28 (2.2%) had syphilis and 105 (8.3%) had herpes. Cases in which no microbiologic aetiology was identified were not more likely to have a repeat clinic visit within 14 days of diagnosis compared with those with Gonorrhea or Chlamydia (6.3% vs. 6.8%).

Conclusion STD clinics can be sentinel sites to assess proctitis trends. No microbiologic diagnosis was identified in almost half of proctitis cases evaluated during the study interval and these cases were not more likely to experience treatment failure, suggesting that current empiric treatment guidelines are effective. Future studies should use advanced molecular techniques to evaluate the role of novel and emerging pathogens in the aetiology of proctitis.