How reliable is self-testing for gonorrhea and chlamydia among men who have sex with men?

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Original Research

How reliable is self-testing for gonorrhea and chlamydia among men who have sex with men?

J Fam Pract. 2013 February;62(2):70-78

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References

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16. Lippman SA, Jones HE, Luppi CG, et al. Home-based self-sampling and self-testing for sexually transmitted infections: acceptable and feasible alternatives to provider-based screening in low-income women in Sao Paulo, Brazil. Sex Transm Dis. 2007;34:421-428.

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20. van der Helm JJ, Hoebe CJ, van Rooijen MS, et al. High performance and acceptability of self-collected rectal swabs for diagnosis of Chlamydia trachomatis and Neisseria gonorrhoeae in men who have sex with men and women. Sex Transm Dis. 2009;36:493-497.

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22. Alexander S, Ison C, Parry J, et al. Self-taken pharyngeal and rectal swabs are appropriate for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae in asymptomatic men who have sex with men. Sex Transm Infect. 2008;84:488-492.

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26. Ota KV, Tamari IE, Smieja M, et al. Detection of Neisseria gonorrhoeae and Chlamydia trachomatis in pharyngeal and rectal specimens using the BD Probetec ET system, the Gen-Probe Aptima Combo 2 assay and culture. Sex Transm Infect. 2009;85:182-186.

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30. Chernesky MA, Hook EW, 3rd, Martin DH, et al. Women find it easy and prefer to collect their own vaginal swabs to diagnose Chlamydia trachomatis or Neisseria gonorrhoeae infections. Sex Transm Dis. 2005;32:729-733.

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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.