CHLAMYDIA IS THE MOST commonly notified sexually transmitted infection (STI) in Australia, with an annual notification rate of 160.7 infections per 100,000 persons in 2003: 40% of infections are diagnosed among men.1 In contrast with earlier opinion,2 a recent review of prospective studies investigating the effectiveness of condom use in preventing STIs found that condom use was associated with statistically significant protection of men and women against chlamydia.3 However, none of these studies reported on the effectiveness of condom use against STI transmission among men who have sex with men (MSM), nor did these studies explicitly assess the effectiveness of condoms against STI transmission during anal intercourse.
The Melbourne Sexual Health Centre (MSHC) is a large, public STI clinic in an Australian capital city, providing free anonymous human immunodeficiency virus and STI testing. We undertook an analysis of its computerized client records to investigate the association of condom use with chlamydia infection in men.
Computerized records for all attendances at the MSHC between July 1, 2002, and June 30, 2003, by men were included in the analysis. Abstracted data included age, number of male and female sexual partners in the last 3 months, use of condoms for vaginal or anal sex in the last 3 months, and chlamydia test result.
Specimens routinely collected from MSM include either a urethral swab or urine specimen and a rectal swab, if indicated in accordance with the Australasian College for Sexual Health Physicians Guidelines for the Management of STIs in Men Who Have Sex With Men.4 Specimens routinely collected from men with heterosexual contact only include either a urethral swab or a urine specimen. All specimens were analyzed for Chlamydia trachomatis using BD ProbeTec Strand Displacement Amplification (SDA).
Separate analyses were performed for men reporting male-to-male sexual contact (MSM) and for men reporting heterosexual contact only (non-MSM). Self reported condom use was classified as never, less than 50% of the time, more than 50% of the time, or always. The rate of chlamydia diagnosis per 100 consultations was calculated for MSM and non-MSM who reported at least 1 sexual partner in the preceding 3 months. Site-specific rates (rectal, urethral, or pharyngeal) were calculated based on individuals who were tested at that specific site. Associations between age, condom use, and number of partners with chlamydia were assessed using general estimating equations, adjusting for multiple visits from an individual. All analyses were conducted using Stata.5
During the study period, there were 4105 consultations with men reporting at least 1 sexual partner in the last 3 months during which a chlamydia test was conducted (1248 MSM and 2857 non-MSM). The age distribution of men at consultation was similar for MSM and non-MSM, with an average age of 33 years at consultation.
Among MSM, genital chlamydia (rectal, urethral, or pharyngeal) was diagnosed during 103 consultations, with a rate of 8.6 cases per 100 consultations (95% CI, 7.1–10.3). The numbers and rates per 100 consultations of rectal, urethral, and pharyngeal chlamydia were 47 (6.2; 95% CI, 4.6–8.1), 59 (5.1; 95% CI, 3.9–6.6) and 7 (1.3; 95% CI, 0.5–2.6). Chlamydia was isolated from 2 or more sites during 9 consultations.
Among non-MSM, urethral chlamydia was diagnosed during 195 consultations, with a rate of 6.8 cases per 100 consultations (95% CI, 5.9–7.8).
Among men who have sex with men (MSM), condom use was associated with a lower odds of rectal chlamydia, but not urethral, infection (Table 1). Among men reporting heterosexual contact only (non-MSM), condom use was associated with lower odds of urethral chlamydia (Table 2).
We found that consistent condom use was protective against acquiring rectal chlamydia infection in MSM. These data make a significant contribution to the evidence base about the effectiveness of condoms against rectal chlamydia in MSM as there is very little published literature.
We did not find an association between chlamydial urethritis and condom use among MSM. This interesting finding raises the possibility that oral sex may play an important role in chlamydial urethritis among men attending MSHC. With the exception of 1 study of STIs in heterosexual men in the United Kingdom that reported 1 case of chlamydial urethritis acquired from oral sex,6 there is little published evidence about oral sex as an independent risk factor for chlamydial urethritis, although pharyngeal chlamydia is well documented.6–12 Oral sex is, however, a recognized means of transmitting gonococcal and nonchlamydial, nongonococcal urethritis in both homosexual and heterosexual men. A cross-sectional study of MSM attending an STI clinic in the United States found that oral insertive sex was independently associated with urethral gonorrhoeae (OR = 4.4) and nonchlamydial, nongonococcal urethritis (OR = 2.2) and that oral sex may account for up to half of all urethral infections in MSM.13 An analysis of the heterosexual men attending the same STI clinic did not find any association between oral sex and urethritis, but the authors concluded that limitations in their analysis did not exclude such an association.14 Others have found that oral sex is the most likely cause of gonococcal or nonchlamydial, nongonococcal urethritis in men.9,15–18
Consistent condom use was protective against acquiring urethral chlamydia in non-MSMs. Similar findings have been reported in another cross-sectional study of heterosexual men and women attending an urban STI clinic in the United States19 and in a recent review of prospective studies investigating the effectiveness of condom use in preventing STIs.3
We did not find an association between the number of sexual partners reported by MSM and rectal infection but did for urethral infection. This may be because a significant number of sexual acts in MSM do not involve anal sex but do involve oral sex, and our data do not differentiate between oral sex and anal sex partners. Furthermore, the association between urethral chlamydia and the number of sexual partners further supports the hypothesis that oral sex may be important in the transmission of urethral chlamydia.
There are a number of limitations in our study design which must be considered when interpreting the results. First, condom use based on self-report is subject to both recall and social desirability bias and does not factor in condom failure or incorrect use.20 Second, we were unable to differentiate between condom use for insertive versus receptive anal intercourse and between regular or casual partners. Finally, we could not determine the infection status of partners, leading to an underestimate of condom effectiveness by including subjects in the analysis not actually exposed to chlamydia. However, this is a significant limitation in many studies of condom effectiveness.21
Despite these limitations, this analysis provides valuable information about the effectiveness of condoms against chlamydia transmission in men, particularly as it differentiates between MSM and non-MSMs. The findings suggest that condoms do provide some protection against rectal chlamydia infection in MSM and chlamydial urethritis in non-MSM but that other factors such as oral sex may play an important role in the transmission of chlamydial urethritis in MSM. Further research is necessary to study the role of oral sex in the transmission of chlamydial urethritis.
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