Comparative Analysis of Smear Testing, In-house PCR and Commercial Real-time PCR for Genital Chlamydia Detection

Introduction: Genital infection caused by Chlamydia trachomatis serovars D-K is the commonest bacterial sexually transmitted disease (STD) with the highest prevalence seen among youth. The objectives of the study were to determine the effectiveness of smear testing in diagnosing chlamydia infection, provide an alternative diagnostic test (in-house conventional polymerase chain reaction) for the detection of chlamydia, and compare it with a commercial rt-PCR as the reference test.
Methods: The study was a cross-sectional, descriptive study enrolling 216 female and 252 male consecutive adult attendees of the Central STD Clinic, Colombo. Gram stain of cervical smear, urethral smear, and urine was carried out and compared with the reference standard of COBAS® TaqMan® CT v2.0 rt-PCR on endocervical swabs from females and urine from males. In addition, a comparative study was conducted on 50 endocervical swabs to compare the commercial real-time (rt)PCR with the conventional in-house PCR.
Results: Cervical smears , urethral smears in females and males, and urine deposits in males had sensitivity of 10-50% and specificity of 0-99.4% compared to the reference test. The in-house PCR had sensitivity, specificity, positive and negative predictive values, diagnostic accuracy, positive likelihood ratio, and negative likelihood ratio of 91.3%, 96.3%, 95.4%, 92.8%, 94%, 24.6 and 0.09, respectively, when compared to the reference test.
Conclusion: This study concluded that smear tests are not effective in diagnosing genital chlamydia infection. The PCR assay evaluated in this study can significantly improve the sensitivity and specificity of diagnosing genital chlamydia infection in the local setting.