Background: Men who have sex with men (MSM) have high rates of gonococcal infection. In San Francisco, more than one half of these infections occur in MSM, and previous cross-sectional studies have reported a prevalence of up to 15.3 percent in this group. Many cases of pharyngeal gonorrhea are believed to be undiagnosed because of inadequate screening, although the Centers for Disease Control and Prevention (CDC) recommends at least annual screening in MSM. Because oral sex has been associated with a greater risk of urethral gonorrhea, asymptomatic pharyngeal infections may serve as an unrecognized reservoir for transmission. Morris and colleagues studied MSM in San Francisco to determine the incidence and prevalence of gonorrhea infection in this population.

The Study: Participants in the longitudinal study were 18 years and older, were negative for human immunodeficiency virus (HIV) antibodies at baseline, had more than one sex partner within the previous two years, and had anal sex with at least one man within the previous year.

Participants were interviewed and examined semiannually over 28 months. They were asked about recent oral sex behavior including number of episodes, whether ejaculation occurred, number of insertive (having a partner's penis in his mouth) or receptive (having his penis in a partner's mouth) partners, and how many sore throats they had within the previous three months. They were also asked whether they knew the HIV status of recent partners. Pharyngeal swabs were obtained at each visit for gonorrhea testing, and consenting participants were screened for rectal and urethral gonorrhea.

Results: The 603 participants had a mean age of 36 years, and 71 percent were white. Participants attended 97 percent of scheduled follow-up visits. Twenty-four participants were excluded because of HIV seroconversion during the study. High-risk sexual behavior was common: two thirds of participants reported that within the six months before the study they had had unprotected anal sex; 45 percent had had unprotected anal sex with partners who were HIV-positive or who were unaware of their status; and 41 percent reported having had unprotected receptive oral sex with ejaculation during this period.

During the study, 18 percent of participants had at least one positive pharyngeal gonorrhea test, and 20 percent of these participants had more than one case of gonorrhea. There was no association between pharyngeal symptoms and a pharyngeal gonorrhea diagnosis. Overall, 2,475 pharyngeal swabs, 1,374 urethral swabs, and 851 rectal swabs were obtained for testing. The prevalence and incidence of pharyngeal gonococcal infection was significantly higher than rectal or urethral gonococcal infections (see accompanying table).

A pharyngeal gonorrhea diagnosis was associated with younger age, having had more insertive oral-sex partners within the previous three months, and having at least one HIV-positive partner. Black men were less likely to contract gonorrhea than white men, although the reason for this is unclear. Multivariate analysis showed that not allowing partners to ejaculate in the mouth was not associated with any protective effect.

Conclusion: The authors conclude that pharyngeal gonorrhea is often asymptomatic, is more common than rectal or urethral gonorrhea in MSM, and may serve as an important reservoir for genital infection. This study supports the CDC's 2002 sexually transmitted disease screening guideline for MSM, which recommends pharyngeal gonorrhea screening at least annually and every three to six months in patients with multiple anonymous partners or in those who use illicit drugs while having sex.