**4. The journey of diagnostics for chlamydia**

The diagnostic methodology of chlamydia has undergone a transformative change over the last two decades spanning from the traditional culture to high throughput NAAT (nucleic acid amplification test)/NGS (next generation gene sequencing). Testing for chlamydia infection is indicated for patients having ocular, urogenital and anorectal symptoms. Close contacts of such patients should also be tested for chlamydia and other sexually transmitted infections along with medico legal cases destined for such testing.

Laboratory investigations include both direct and indirect methods. Direct methods depend on detection of the antigen or nucleic acid. It includes culture, antigen tests (Enzyme Immune Assay, direct fluorescent antibody (DFA), and immune chromatographic RDTs), nucleic acid hybridization and amplification tests. Indirect methods detect antibodies against CT and have a role in diagnosing chronic and invasive infection like pelvic inflammatory disease (PID), lymphogranuloma venerum (LGV) and post infectious complications, like sexually acquired reactive arthritis (SARA) [33]. As *C. trachomatis* crosses the epithelial barrier and may no longer be detectable in swabs in these chronic/invasive infections. However, serology is not recommended for diagnosis of acute genitourinary infections, as the antibody response comes into play only after weeks to months of infection and the titers are usually insignificant.
