We also found that rectal chlamydia or gonorrhea positivity varied by age, with the levels highest among those in the youngest age groups (Table 2). Furthermore, rectal STI positivity varied by behavioral risk factors. In STD clinic visits by young women (≤25 years), rectal chlamydia or gonorrhea was more prevalent based on reported sex partner characteristics. Specifically, visits in which women reported a recently incarcerated sex partner (21.1% vs. 15.3%, P = 0.05), a sex partner with injection drug use (46.5% vs. 15.5%, P < 0.01), or an HIV-positive sex partner (66.7% vs. 15.8%, P = 0.02) had a higher percent positivity for rectal chlamydia or gonorrhea. Likewise, the proportion of women visits with a positive rectal test result was higher among those with a concurrent urogenital infection as compared with those without a urogenital infection (54.2% vs. 6.6%, P < 0.01). In visits by women older than 25 years, no differences were noted in rectal chlamydia or gonorrhea percent positivity by sexual risk behaviors, except for substance use (Table 2). Specifically, 10.6% of women visits with reported substance use had a positive rectal chlamydia or gonorrhea test result as compared with 5.8% of visits in which substance use was not reported (P < 0.01). Similar to younger women, the proportion of positive rectal chlamydia or gonorrhea was higher in visits where a concurrent urogenital infection was identified (55.3% vs. 4.0%; P < 0.01).
On the basis of multivariable analyses, factors associated with rectal chlamydia or gonorrhea varied by age group (Table 3). Among women in the younger age group, after controlling for the presence of a concurrent urogenital chlamydia or gonorrhea infection, those who reported a sex partner with injection drug use were nearly five times as likely to test positive for rectal chlamydia or gonorrhea (adjusted odds ratio [AOR], 4.78; 95% confidence interval [CI], 1.02–22.45). Likewise, having an HIV-positive sex partner was also associated with rectal chlamydia or gonorrhea (AOR, 4.85; 95% CI, 1.02–22.93). Among women 26 years or older, after adjusting for a concurrent urogenital infection, those who reported substance use were more likely to have rectal chlamydia or gonorrhea as compared with those who did not report substance use (AOR, 1.77; 95% CI, 1.04–3.02).
Findings from this study indicate that rectal chlamydia and gonorrhea positivity among women who report AI is similar to that of urogenital infections. We also found that up to one third of cases—more so for chlamydia than gonorrhea—would be missed in the absence of rectal testing. Furthermore, the relatively large study population and high occurrence of rectal chlamydia and gonorrhea allowed us to further explore factors associated with these infections. To our knowledge, this is one of the first studies to report an independent association between sexual risk behaviors and rectal chlamydia and gonorrhea among women even after controlling for multiple other known risk factors for STIs. In addition, we were able to demonstrate that factors predictive of rectal STIs among women varied by age.
Consistent with the few studies that have been published thus far, we found that rectal chlamydia and gonorrhea positivity among women was comparable with that of urogenital infections.13–15 Previous studies have demonstrated the importance of extragenital testing among MSM, with evidence indicating that a third and as much as 64% of gonorrhea infections and 53% of chlamydia infections would be missed in the absence of rectal testing.9,19 In these studies, the prevalence of rectal-only infections was high, and the proportion of infections that were dual infections at both urethral and rectal sites were low. These findings are different from our study, which show a higher level of concordance between rectal and urogenital infections. This difference may partly be explained by sexual and risk behavior differences when comparing MSM with women but also anatomical differences, which limit the potential for spread of contaminated secretions and fluids from the urogenital site to the rectum. Although rectal testing data on women have been limited, in a study among women attending an STD clinic in San Francisco, rectal swabs were collected from women receiving a pelvic examination, regardless of whether they reported AI. In this study, the overall prevalence of rectal and urogenital chlamydia/gonorrhea was 6.0% and 6.7%, respectively, and rectal testing increased chlamydia and gonorrhea case finding by 14.8%, which is substantially lower than the 23% to 34% noted in our study.14 This difference is likely because the San Francisco study included women who did not report AI and were therefore at lower risk of rectal infection. Our findings support the author’s suggestion that the utility of rectal screening is likely to be higher in a population with a higher overall prevalence of chlamydia and gonorrhea.
In fact, the personal and public health benefits of rectal testing in women are unclear. First, although rectal infections among women may result from unprotected AI, it is possible that infected vaginal secretions may result in a false-positive rectal test result.20,21 Second, screening and treating women for urogenital tract infections with chlamydia and gonorrhea has been proven to reduce the incidence of pelvic inflammatory disease and other reproductive health sequelae such as ectopic pregnancy, infertility, and chronic pelvic pain.22–24 In contrast, the health benefit of rectal screening for women has yet to be determined. However, given that all the women in this study reported anal intercourse and many reported additional high-risk behaviors, testing and treating these women not only has implications in reducing HIV risk25,26 but in the absence of testing/treatment, the opportunity for chlamydia or gonorrhea transmission to partners and re-infection of these women seem great.
We also found that rectal chlamydia and gonorrhea positivity was higher among those who were younger, with positivity as high as 21.3% among those in the youngest age group. Furthermore, among those 25 years or younger, rectal positivity was significantly higher among women who had a sex partner who reported injection drug use or was HIV positive. The association remained even after controlling for the potential overlap in risk factors associated with having a urogenital infection. This finding is not surprising given that the prevalence of sexual risk behaviors and STIs are much higher among both injection drug users and those who are HIV positive.27–30 This suggests that women with rectal chlamydia or gonorrhea likely belong to sexual risk networks with very high STI and HIV transmission probabilities. Although none of the women in this study were HIV positive, these findings highlight the importance of rectal testing and stress the importance of specific counseling messages for women related to the risks associated with unprotected AI.
Our findings should be interpreted in light of some of the limitations of this study. Owing to the sensitivity of nucleic acid amplification testing, it is possible that some positive test results were not true rectal infections but rather were caused by cross contamination in women with urogenital chlamydia or gonorrhea. This would have resulted in a higher estimate of overall rectal disease prevalence but should not significantly impact the rectal-only disease prevalence nor its contribution to increased case finding. Assessment of AI and other sexual risk behaviors was based on self-report and assessed by clinic staff using face-to-face interview methods. Although this information was collected in the context of health care, interview-based data on socially stigmatized or illicit activities may suffer from reliability and validity issues. During an interview, patients may be reluctant to disclose information regarding sensitive, socially stigmatized, or illegal activities, resulting in response bias and a potential underestimation of these behaviors.31–33 Given that rectal swabs are only collected from women who report AI, the potential underreporting of AI may have biased our estimates of rectal chlamydia and gonorrhea. Furthermore, not all women reporting AI had a rectal swab collected. Although there were no differences in sexual risk behaviors, the difference in rectal testing by age may have also biased our estimates of rectal chlamydia and gonorrhea. Finally, this study was based on participants who attended public STD clinics and therefore may not be generalizable to other populations.
Our results indicate that levels of rectal chlamydia and gonorrhea among women at STD clinics who report recent AI are similar to that of urogenital infections. Furthermore, our findings highlight the fact that a relatively large number of infections in this population would be missed in the absence of rectal testing. We also found that women with rectal chlamydia or gonorrhea were more likely to report individual and sexual network characteristics that place them at high risk for continued transmission and acquisition of STIs including HIV. These results have implications for those who provide medical care to clients at STD clinics and highlight the need for rectal screening recommendations for women, specific patient counseling messages related to condom use for AI, the risks associated with unprotected AI and substance use, and the increased risk for the transmission or acquisition of HIV and other STIs.
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