The aim of our study, therefore, was to explore the ability of MSM patients to perform both pharyngeal and rectal testing for gonorrhea and chlamydia by evaluating the concordance of patient- and provider- administered testing results. We designed the study so that both patients and trained providers performed testing using Gen-Probe’s APTIMA Combo 2 (AC2) kits at pharyngeal, rectal, or both sites, depending on the patient’s recent sexual practices. As discussed, prior studies suggested that concordance would be good for rectal swab specimens. But only one study had examined pharyngeal swab concordance in addition to rectal, and it led to concerns about patient-generated false positives. We wanted our study to evaluate whether patient-administered testing produced accurate results for both pharyngeal and rectal specimens, and whether patient testing behaviors led to cross-contamination and subsequent false-positives when performing both tests.
METHODS
Patient recruitment and eligibility
We recruited patients from STI testing clinics and from primary and HIV care clinics at the Whitman-Walker Clinic in Washington, DC from September 15, 2009 to April 19, 2011. Eligible participants were men who’d had sex with men in the last 6 months and who wanted testing for gonorrhea and chlamydia. The presence of symptoms, reports of condom use during sex, and HIV status did not affect eligibility.
Interested patients signed a consent form and completed a behavioral questionnaire, which included questions about demographics and sexual behavior. A patient’s responses to this questionnaire determined whether he was eligible to participate and the type of testing needed. For example, if a patient had had only oral or anal sex but not both, we limited testing to either pharyngeal or rectal swabbing.
Testing procedures
We randomized patients to either perform self-testing first or to have provider-administered testing first. When patients were ready to self-administer the swabs, we gave them placards that explained how to properly collect samples23 and Gen-Probe AC2 testing kits (Hologic Gen-Probe, San Diego, Calif) for each test they needed to perform. The provider remained in the room while the patient performed the testing to ensure that the patient made an attempt at screening and to identify any common problems with the instructions. If the provider observed problems with how the patient performed the screening, he or she recorded that on a spreadsheet after the patient left.
The 4 providers who performed testing (a nursing student, a medical student, and 2 clinical research assistants) had all been previously trained in STI testing techniques by clinic MDs. When these providers performed testing, they swabbed the patient twice at each site. One of these swabs was stored for research testing, and the other went immediately to the clinic laboratory for testing so that the patient could receive the standard of care antibiotic treatment if the test was positive. The designated research samples were tested in a Gen-Probe laboratory in California.
Statistical methods
Based on a previous study by Lampinen et al that examined concordance between patient- and provider-obtained rectal swabs, we planned on a total sample of 360 patients to achieve 80% power in detecting a difference in positive tests of 5% between patients and clinicians at a one-sided 5% significance level.24 This plan assumed that the percentage of discordant pairs would be 15%, where one pair consists of one test result each from a clinician and a patient at the same site. We performed sample-size calculations in nQuery Advisor version 6.0 (Statistical Solutions, Saugus, Mass). Ultimately, we enrolled 374 men in the study. We tested 5 patients twice, but only their first screening was included in the primary analyses.
We entered demographic and behavioral data from the patient questionnaires into an online database. We also generated descriptive statistics for demographics and baseline characteristics from the questionnaires.
We performed an exact McNemar’s test for each anatomic site and STI to evaluate whether there were significant differences between patient- and provider-performed swabs. We also calculated Kappa coefficients for each site and STI as a measure of concordance. We regarded as positive any test results that were equivocal, because in clinical practice a provider would likely provide treatment. However, we also performed McNemar testing and Kappa calculations with these results excluded and classified as negative to ensure that no significant differences resulted. We evaluated statistical significance at the 0.05 level (2-sided), and performed all analyses in SAS software version 9.2 (SAS Institute, Cary, NC).
RESULTS
The patients who enrolled in the study represented a wide range of ages and ethnic backgrounds, with a median age of 33 years and with Caucasian patients accounting for 54.8%. Patients who had had sex with only men in the past year accounted for 89.8% of the sample, while 8.6% had both male and female partners (the final 1.6% had either no sex partners or missing data). The average number of male partners in the last 2 months was 2. As for sexual practice, 86.9% had insertive oral intercourse in the past year, 70.8% had insertive anal intercourse, 87.2% had receptive oral intercourse, and 67.9% had receptive anal intercourse (TABLE 1).