Similar to N gonorrhoeae, Chlamydia trachomatis causes infections of the pharynx, urethra, and rectum in MSM. Chlamydia is better recognized as an asymptomatic or minimally symptomatic infection. Recent data on rectal chlamydial infections in MSM show increases over the past 5 years and a 10% prevalence of asymptomatic infection. Additionally, studies in MSM show that chlamydia may cause up to 20% of cases of nongonococcal urethritis (NGU), similar to the proportion of NGU attributable to chlamydia in heterosexual men. In asymptomatic populations of MSM undergoing urine screening for urethral chlamydial infection at anonymous HIV testing sites, 0.5% had chlamydial infection in Denver and 3% in San Francisco. Data on pharyngeal chlamydia suggest the prevalence is low, ranging from 0.5% to 2%. (more…)