From July 2003 through February 2007, 441 test sets were collected from 377 individuals. Of these test sets, 375 gonococcal test sets were contributed by 334 eligible individuals, and 387 chlamydial test sets were contributed by 351 individuals that were evaluable for the purposes of analysis. Among the 66 excluded rectal gonorrhea test sets, 22 (33.3%) were excluded because one or more tests in the set contained a result that was neither positive nor negative (i.e., unevaluable results for PCR [17 sets], TMA [three sets], or SDA [two sets]), nine (13.6%) sets were excluded due to incomplete collection of the set, 12 (18.2%) were excluded because they were recollections immediately following a positive test, and 12 (18.2%) were excluded due to collection <30 days following a previously negative test set for gonorrhea at the rectal site. Among the 54 excluded rectal chlamydial test sets, 17 (31.5%) were recollections following a positive test, 12 (22.2%) were excluded because one or more tests in the set contained a result that was neither positive nor negative (i.e., nine sets due to unsatisfactory or inconclusive culture, and one set each for unevaluable PCR, TMA, and SDA results), eight (14.8%) sets were excluded due to incomplete collection of the set, and six (11.1%) were excluded due to collection <30 days following a previously negative test set for chlamydia at the rectal site. Eleven sets from both the gonococcal and chlamydial test sets were excluded due to lack of rectal exposure within the defined 2-month time frame (16.7% and 20.4%, respectively).
The study population (Table ) differed significantly by gender in terms of age, racial group, and recruitment site. As specified by enrollment criteria, all of the men reported rectal exposure. Among women, rectal exposure was reported by 40.4%. Among the 99 female patients, 26 (27.3%) reported contact with gonorrhea, chlamydia, or NGU, while 36 (36.4%) were enrolled because they presented to clinic with untreated gonorrhea and/or chlamydia (Table ). Seven (25.9%) women reporting contact with STD, and two (7.4%) women presenting with untreated chlamydial infection also reported rectal sexual activity (data not shown). Symptoms consistent with rectal infection were reported in a minority of the study population (11.6% of men and 3% of women).
Test sensitivity was first calculated using a rotating standard which compared each test under evaluation with a performance standard defined as any two positive tests of three comparator tests (two-of-three standard). A second standard was applied in which each test was consecutively compared to a performance standard defined as three positive tests of three comparator tests (three-of-three standard). Based on a rotating gold standard of two of three comparator tests being positive, test sensitivity for the detection of N. gonorrhoeae was 66.7% (95% confidence interval [CI], 49.0% to 81.4%) for culture and, for the NAATs, ranged from 91.4% (95% CI, 76.9% to 98.2%) for PCR to 100% (95% CI, 89.4% to 100%) for TMA (Table ). Specificities were high at 100% (95% CI, 98.9% to 100%) for culture and greater than 98% for all three NAATs. Using the three-of-three reference standard, test sensitivities were 71.9% (95% CI, 53.3% to 86.3%) for culture, 95.8% (95% CI, 78.9% to 99.9%) for PCR, and 100% (95% CI, 85.2% to 100%) for TMA and SDA. Specificities remained high—99.7% (95% CI, 98.4% to 100%) for culture—but were substantially lower—95.5% (95% CI, 92.7% to 97.4%) to 96.0% (95% CI, 93.4% to 97.8%)—for the NAATs (Table ).
Estimates of SDA, PCR, TMA, and culture sensitivities and specificities for detection of N. gonorrhoeae or C. trachomatis by reference standard
Similarly, when the performance for C. trachomatis detection was calculated, test sensitivity was only 36.1% (95% CI, 24.2 to 49.4%) for culture but, for NAATs, ranged from 80.7% (95% CI, 68.1% to 90.0%) for PCR to 100% (95% CI 92.5 to 100%) for TMA, utilizing the two-of-three reference standard, and, utilizing the three-of-three reference standard, was only 45.7% (95% CI, 30.9% to 61.0%) for culture but 95.5% (95% CI, 77.2% to 99.9%) for PCR and 100% (95% CI, 83.9% to 100%) for TMA and SDA. Specificities of the NAATs ranged from 95.6% (95% CI, 92.8% to 97.5%) to 98.5% (95% CI, 96.5% to 99.5%) when the two-of-three standard was utilized and from 88.8% (95% CI, 85.1% to 91.8%) to 91.8% (95% CI, 88.5% to 94.4%) for the three-of-three reference standard and were higher for culture with each standard (Table ).
We calculated the prevalences of N. gonorrhoeae and C. trachomatis based on a composite test measure, with infection defined as a positive culture and/or two or more positive NAATs. Among men, all of whom reported rectal exposure, the prevalence of rectal N. gonorrhoeae infection was 7.9% (95% CI, 5.0 to 11.7%) based on the composite standard, and the prevalence of C. trachomatis infection was 10.3% (95% CI, 7.1 to 14.4%) (Table ). Prevalence of N. gonorrhoeae in females ranged from 5.6% (95% CI, 0.7 to 18.7%) in women with rectal exposure to 19.2% (95% CI, 6.6 to 39.4%) in women reporting contact with an STD. C. trachomatis prevalence in women was 23.1% (95% CI, 11.1 to 39.3%) in women engaging in rectal sex and over 50% in women presenting for treatment for a previously diagnosed STD (Table ).
Rectal N. gonorrhoeae and C. trachomatis prevalence by reason for enrollment
One hundred fifty-one men and 84 women received chlamydial and/or gonococcal genital testing. With genital infection defined as a positive standard of care test and rectal infection defined as a positive culture and/or two or more positive NAATs, 19 gonococcal infections and 19 chlamydial infections were identified at the rectal and/or genital site in male participants (Table ), with 63.2% of gonococcal infections and 84.2% of chlamydial infections present at the rectal site only. Among female participants with genital and rectal test results available, 3 (15.8%) of the 19 with gonococcal infection and 7 (23.3%) of the 30 with chlamydial infection were infected only at the rectal site. Compared to females without rectal exposure, females reporting rectal sex were more frequently infected only at the rectal site. However, only 4 of the 19 females with gonococcal infection and 7 of the 30 females with chlamydial infection reported rectal exposure.
Gonococcal or chlamydial infection by site among enrollees tested at both genital and rectal sites and infected at one or both sites