DNA amplification assays: A new standard for diagnosis of Chlamydia trachomatis infections

Chlamydia trachomatis infection is one of the most common causes of sexually transmitted infections in the world. Due to their significant morbidity, their economic impact, and the fact that they are often asymptomatic, recommendations have been made that widespread screening of those individuals at most risk be performed. However, screening for C. trachomatis infections has been hampered in the past by the lack of sensitive, specific, and simple laboratory procedures. Until recently in vitro culture was considered to be the 'gold standard' for detection of chlamydia, but it was expensive, technically complex, and was known to be only 50-85% sensitive compared to nucleic acid amplification assays. With the introduction of new DNA amplification techniques, such as polymerase chain reaction (PCR) and ligase chain reaction (LCR) assays, there are now commercial tests that have sensitivities of 90-96% and specificities of 98-100%. These assays are especially attractive since they can be used with either cervical and urethral specimens, or urine which offers a non-invasive approach for large scale screening programs. Although the commercial assays utilise a chlamydial plasmid gene for amplification, the gene encoding the major outer membrane (omp1), has been used to generate PCR products for both nucleic acid sequencing and restriction fragment length polymorphism (RFLP), in order to better define the molecular epidemiology of C. trachomatis. Other DNA amplification assays, such as Q-beta replicase and transcription-mediated amplification (TMA), are also currently being developed for detection of C. trachomatis infections. PCR and LCR are both useful for detection of C. trachomatis in other types of clinical specimens, such as ocular specimens, tissue from cases of reactive arthritis, salpingitis, and tubal factor infertility. DNA amplification assays offer a valuable method to supplement chlamydia control programs by increasing the sensitivity and specificity of detection and treatment.