How reliable is self-testing for gonorrhea and chlamydia among men who have sex with men?
Our study shows that patients who collected their own rectal and pharyngeal samples had test results that were of equal or better accuracy than those of clinical providers.
Considering only provider-identified positives, 5.1% of the patients tested positive for rectal gonorrhea, 11.6% for rectal chlamydia, 6.3% for pharyngeal gonorrhea, and 0.8% for pharyngeal chlamydia (TABLE 2). Considering both provider- and patient-identified positives, 8.0% of patients tested positive for rectal gonorrhea, 9.3% for pharyngeal gonorrhea, 12.7% for rectal chlamydia, and 1.3% for pharyngeal chlamydia. Five equivocal results were identified—2 for a patient rectal gonorrhea test, one for a patient pharyngeal gonorrhea test, one for a provider pharyngeal gonorrhea test, and one for a provider rectal chlamydia test.
In only one case did a provider identify a positive result when the patient’s result was negative. In 23 cases, however, the patient identified a positive result when the provider’s result was negative. Patients identified significantly more positives for rectal and pharyngeal gonorrhea than providers, but there were no significant differences in patient and provider results for the chlamydia tests.
Even with these 24 discordant results, there was ≥75% concordance between patient and provider results on all tests, with very strong concordance (95%) for rectal chlamydia results (TABLE 2). When we re-ran the McNemar tests and the Kappa coefficients with equivocal results considered missing and negative, there were no statistically significant differences when compared with the calculations done with equivocal results considered positive.
Some difficulties observed with self-testing. Observing providers noted anecdotally that there were minor difficulties with the self-administered testing instructions. Three patients spilled the preservative liquid in which swabs are placed, 5 patients used the incorrect swab to perform testing, and 2 other patients had samples that were noted as compromised by the provider. None of these documented problems involved the 24 discordant cases.
TABLE 1
Characteristics of men participating in the study
| Demographic | N=374 |
|---|---|
| Age, y | |
| Median | 33 |
| Range | 18-70 |
| n (%) | |
| Race/ethnicity | |
| White/non-Hispanic | 205 (54.8) |
| Black/non-Hispanic | 85 (22.7) |
| Latino/Hispanic | 40 (10.7) |
| Asian | 13 (3.5) |
| Mixed | 8 (2.1) |
| Other | 19 (5.1) |
| Missing data | 4 (1.1) |
| Modes of GC/CT testing | |
| Rectal and pharyngeal | 272 (72.7) |
| Rectal only | 5 (1.3) |
| Pharyngeal only | 97 (25.9) |
| Sexual partner(s) in the last 12 months | |
| Men | 336 (89.8) |
| Men and women | 32 (8.6) |
| None | 1 (0.3) |
| Missing data | 5 (1.3) |
| Number of male sexual partners in the past 30 days | |
| 0-1 | 178 (47.6) |
| 2-3 | 130 (34.8) |
| 4 or more | 64 (17.1) |
| Missing data | 2 (0.5) |
| Number of male sexual partners in the past 60 days | |
| 0-1 | 104 (27.8) |
| 2-3 | 135 (36.1) |
| 4 or more | 133 (35.6) |
| Missing data | 2 (0.5) |
| Practiced insertive oral intercourse in past 12 months | |
| Yes | 325 (86.9) |
| No | 20 (5.4) |
| Missing data | 29 (7.7) |
| Practiced insertive anal intercourse in past 12 months | |
| Yes | 265 (70.8) |
| No | 78 (20.9) |
| Missing data | 31 (8.3) |
| Practiced receptive oral intercourse in past 12 months | |
| Yes | 326 (87.2) |
| No | 20 (5.3) |
| Missing data | 28 (7.5) |
| Practiced receptive anal intercourse in past 12 months | |
| Yes | 254 (67.9) |
| No | 90 (24.1) |
| Missing data | 30 (8.0) |
| CT, Chlamydia trachomatis; GC, Neisseria gonorrhoeae. | |
TABLE 2
Comparison of provider and patient testing results for GC/CT by anatomic site reveals ≥75% concordance on all tests
| Patient test result | Total tests, N | Provider positive test result, n (%) | Provider negative test result, n (%) | P value | Kappa coefficient |
|---|---|---|---|---|---|
| Rectal GC Patient positive test result Patient negative test result | 276 | 14 (5.1) 0 | 8 (2.9)* 254 (92) | <.01 | 0.76 |
| Pharyngeal GC Patient positive test result Patient negative test result | 367 | 23 (6.3) 1 (0.3)* | 10 (2.7)* 333 (90.7) | .01 | 0.79 |
| Rectal CT Patient positive test result Patient negative test result | 276 | 32 (11.6) 0 | 3 (1.1)* 241 (87.3) | .25 | 0.95 |
| Pharyngeal CT Patient positive test result Patient negative test result | 367 | 3 (0.8) 0 | 2 (0.5)* 362 (98.7) | .50 | 0.75 |
| CT, Chlamydia trachomatis; GC, Neisseria gonorrhoeae. *Discordant patient-provider test results. | |||||
DISCUSSION
The prevalence of gonorrhea and chlamydia in this study population was similar to what has been observed in previous studies of MSM,1-4 which confirms the need for improved detection of infections. Self- administered testing is one possible means of increasing the number of patients who are screened and treated, as the results of this study suggest it is equally or more accurate than provider-administered testing at detecting cases of gonorrhea and chlamydia.
Patient and provider results were equivalent for chlamydia detection, and patients appeared to identify more cases of gonorrhea, although interpretation of the significance of this finding is difficult given the relatively small number of cases. However, it is likely that the 23 cases in which patients identified positives that providers did not were true positives, given the sensitivity (84%-100%) and specificity (≥99.4%) of the AC2 test for detecting GC and CT.25
Assuming that our population has a similar prevalence of these STIs as prior studies, we would expect positive predictive values of approximately 100% for rectal GC, 95% for pharyngeal GC, 86.4% for rectal CT, and 71.4% for pharyngeal CT.26
Possible explanations for patients achieving better results than providers in some cases. The most likely explanation for better patient performance on some of the tests is that patients swabbed more meticulously and contacted more surface area.
This was also seen in a study that compared the ability of patients and physicians to identify human papillomavirus infection in swabs taken from areas where skin scraping had been performed. Patients were found to collect an appropriate sample significantly more often, which was thought to be due to physician hesitation to thoroughly scrape the patient’s skin.27 In our study, patients were anecdotally observed to be less likely to gag on a self-administered throat swab and to have less visible tensing of the rectal sphincter on self-administered rectal swab, which could have contributed to improved results.
