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Journal of Clinical Microbiology, February 2009, p. 475-476, Vol. 47, No. 2
0095-1137/09/$08.00+0     doi:10.1128/JCM.01975-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Clinic-Based Evaluation of a Rapid Point-of-Care Test for Detection of Chlamydia trachomatis in Specimens from Sex Workers in Escuintla, Guatemala{triangledown}

M. Sabidó,1,2,3* G. Hernández,4 V. González,5 X. Vallès,1 A. Montoliu,3,5 J. Figuerola,1 V. Isern,5 B. Viñado,6 L. Figueroa,7 and J. Casabona1,2,3,5

Fundació Sida i Societat, Barcelona, Spain,1 PhD Programme in Public Health and Methodology of Biomedical Research, Department of Paediatrics, Obstetrics and Gynaecology, and Preventive Medicine, Universitat Autònoma de Barcelona, Bellaterra 08193, Barcelona, Spain,2 CIBER Epidemiología y Salud Pública, (CIBERESP), Spain ,{dagger},{dagger} Fundació Sida i Societat, Escuintla, Guatemala,4 Center for Epidemiological Studies on HIV/AIDS and STI of Catalonia (CEEISCAT), ICO/Health Department, Badalona, Spain,5 Clinical Laboratory of Primary Health Bon Pastor, Barcelona, Spain,6 Primary Health Care Centre, Escuintla, Guatemala7

Received 13 October 2008/ Accepted 22 November 2008


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ABSTRACT
 
We evaluated a rapid point-of-care test for the detection of Chlamydia trachomatis in specimens from 278 sex workers attending sexually transmitted infection clinics in Guatemala. The sensitivity and the specificity of the test compared to the results of PCR were 62.96% and 99.60%, respectively. The test performed moderately well as a screening tool in a context in which clinical follow-up visits are infrequent.


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TEXT
 
Laboratory screening has been suggested to be an effective strategy for reducing the prevalence of Chlamydia trachomatis infection in sex workers (SWs) (11). Rapid point-of-care (POC) tests can be a cost-effective strategy for increasing the impact of screening interventions for sexually transmitted infections (STIs) in both SWs and their clients (14). Their greatest value is that they can yield the results at the time of the initial patient visit and do not require patient follow-up (6), the rate of failure of which is as high as 50% among STI clinic populations (10). The use of rapid POC tests of moderate sensitivity combined with immediate on-site treatment may lead to the treatment of more infected women than the use of PCR alone when the return rate is low (3). The currently available rapid tests for the detection of C. trachomatis have reasonable specificities, but they are relatively insensitive compared to other methods (7). Their reported sensitivities and specificities for endocervical swab specimens are 49.7% to 95% and 97.9% to 100%, respectively, compared with the results of PCR (4, 5, 7, 8, 9, 17). The Sexually Transmitted Diseases Initiative claimed as a priority the evaluation of rapid C. trachomatis tests that can be used to screen high-risk populations (16). Our aim was to evaluate the performance of a rapid C. trachomatis test compared with that of the current "gold standard" assay (PCR) with specimens from female SWs in the context of its specific application.

Study setting and populations. The study was conducted in three STI clinics located in the province of Escuintla, Guatemala. The clinics were set up by the Fundació Sida i Societat, a nonprofit organization that has been offering to SWs regular screening and treatment for human immunodeficiency virus infection and STIs since 2004. Between April and August 2007, we recruited consecutive female SWs attending the clinics who were at least 18 years of age, willing to participate, and not currently menstruating and who had not used antibiotics within the previous 3 weeks. The women were interviewed, and specimens were collected by trained medical doctors. Testing for C. trachomatis is included in the regular screening for SWs, for which written consent is obtained. Therefore, consent specifically for this study was considered unnecessary.

Specimen collection, transport, and processing. Two cervical swab specimens were collected from each participant and were always collected in the same sequence (a sample was collected for the rapid test, followed by collection of a sample for PCR). We used a Dacron swab to collect samples for the rapid C. trachomatis test, and the samples were tested at the local laboratories on the day of their collection. The specimens used for PCR testing were obtained with a Cervex-Brush (Rovers Medical Devices B.V., Oss, The Netherlands), and after the specimens were collected the brushes were immediately suspended in PresrvCyt solution (Cytyc Corp., Marlborough, MA). The specimens were stored at 4 to 8°C degrees until their shipment and processing at the laboratory of Bon Pastor in Barcelona, Spain. We performed the rapid test with a Chlamydia test card and PCR, as described below.

(i) Chlamydia test card. The Chlamydia test card (Ultimed Products, GmbH, Germany) was the test used by the STI clinics at the time of the study. This is a rapid chromatographic immunoassay whose results are interpreted visually. Chlamydial antigen is extracted from the specimen by inserting the swab in an extraction tube with extraction buffer. The extracted antigen solution is added to the sample window containing an antibody to Chlamydia coated onto particles. The results can be read after 15 min.

(ii) PCR. The Amplicor CT/NG test (Roche Molecular Systems, Inc., Branchburg, NJ) was used to perform the PCR assay. For each amplification assay, a 250-µl sample was transferred into a 2-ml propylene tube. The tubes were centrifuged at 12,000 x g for 10 min. The supernatants were discarded, and the cellular pellet was used for DNA extraction. CT/NT Amplicor lysis buffer (250 µl) was added to the pellet. The contents were mixed well by vortexing. After 15 min of incubation at room temperature, 250 µl of CT/NG specimen diluent was added to the lysate. After another vortexing of the treated sample, 50 µl of the treated sample was used to perform the PCR assay, according to the manufacturer's instructions.

Data analysis. Data were analyzed with the Stata/SE (version 9.0) program (Stata, College Station, TX). The performance characteristics (sensitivity, specificity, and positive and negative predictive values) were calculated by standard methods and are presented with the 95% confidence intervals (CIs), calculated by an exact method (2). Specimens with indeterminate results by the rapid POC test were considered negative.

We recruited 278 female SWs. However, two specimens were excluded from the performance evaluation as there was insufficient sample for the PCR analysis. All participants were asymptomatic. The sensitivity and specificity of the C. trachomatis rapid tests compared to the results of PCR were 62.96% (17/27 specimens; 95% CI, 42.47 to 79.92) and 99.60% (248/249 specimens; 95% CI, 97.43 to 99.98), respectively. The positive and negative predictive values were 94.44% (17/18 specimens; 95% CI, 70.62 to 99.71), and 96.12% (248/258 specimens; 95% CI, 92.77 to 98.02), respectively.

The rapid test performed moderately well in detecting Chlamydia infection among asymptomatic persons who have a low rate of return for follow-up (13). Only 38% of the SWs testing positive for Chlamydia returned for treatment within the agreed-upon time of 7 days. This study reinforces the view that rapid POC tests do have practical utility as screening tools in some settings.

The results of the present study are consistent with those obtained in previous validations of similar assays conducted in the laboratory setting (8) and the clinical setting (3) with specimens from women at high risk for C. trachomatis infection. However, some recent studies of other rapid tests with cervical swab specimens conducted in reference STI clinic settings in developing countries found the sensitivities of rapid tests compared with the results of PCR to be poor (49.7% to 53.5%) (9, 17). The specificity of the rapid POC test was excellent and in the range found in previous evaluation studies in which PCR was used as the reference test (97.9% to 100.0%) (3, 4, 5, 8, 9, 17).

The main limitations of the present study are that the detection of C. trachomatis by use of the rapid test is dependent on the number of organisms present in the specimen and that the detection of the organism may be affected by patient factors, such as vaginal douching, which is a common practice among SWs, and being asymptomatic (17). Although the PCR assay is highly sensitive and specific (1), it can be affected by contamination (12) or inhibitors (15). The rapid tests have been performed in batches by experienced laboratory staff and may not necessarily reflect the performance of the tests in a physician's office. Evaluations that provide the results of the rapid test on a while-you-wait basis need to be performed.


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ACKNOWLEDGMENTS
 
We thank the National AIDS Programme in Guatemala and the CEEISCAT for their trust and support.

The authors have no interest in the manufacturer of the rapid C. trachomatis test, and the authors have no conflict of interest to declare.


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FOOTNOTES
 
* Corresponding author. Mailing author: Fundació Sida i Societat, 179-181 1-1B, Barcelona 08036, Spain. Phone: 34 933 967 820. Fax: 34 932 412 271. E-mail: msabido{at}sidaisocietat.org Back

{triangledown} Published ahead of print on 3 December 2008. Back

http://www.ciberesp.es/. Back


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Journal of Clinical Microbiology, February 2009, p. 475-476, Vol. 47, No. 2
0095-1137/09/$08.00+0     doi:10.1128/JCM.01975-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Gaydos, C. A (2009). Can we climb out of the "pit" of poorly performing rapid diagnostic tests for chlamydia?. Sex. Transm. Infect. 85: 158-158 [Full Text]  

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