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

Infections caused by Chlamydia trachomatis are among the most common bacterial sexually transmitted infections in the world with an estimated 50 million new cases occurring each year. Since the prevalence of chlamydial infections range from 3%-5% among asymptomatic men and women to 20%-25% among adolescents attending sexually transmitted disease (STD) clinics, widespread screening for this infection has been recommended. With the advent of DNA amplification technology, several assays have become commercially available which have high sensitivity and specificity, and can utilise convenient, non-invasive specimens such as urine. Using the endogenous plasmid of C trachomatis as target DNA, polymerase chain reaction (PCR) and ligase chain reaction (LCR) have demonstrated sensitivities of 90% to 96%, with specificities of 98% to 100%. In contrast, culture, the previous gold standard for C trachomatis detection, had sensitivities of 50% to 70% for male urethral specimens and 60% to 80% for female endocervical specimens when compared to confirmed PCR and LCR. DNA sequencing and restriction fragment length polymorphisms (RFLP) of amplified target DNA from the major outer membrane protein gene (OMPI) of C trachomatis has been performed to verify specificity and to study the molecular epidemiology of C trachomatis. Nucleic acid amplification assays have proven to be effective in the detection of chlamydia in other clinical specimens including ocular specimens from patients with trachoma, epididymitis, salpingitis, and reactive arthritis. Urine-based screening of both men and women by LCR or PCR provides a unique sensitive method for widespread population-based screening for C trachomatis, a necessary tenet of chlamydia control programmes.