<prompt> A 30-year-old woman presented with 3 days HO mucopurulent cervical discharge. On gram stain of the discharge, numerous pus cells were seen but no organism was seen. Investigation of choice for diagnosis of this infection?Saline mountCulture in Thayer main mediaNucleic acid amplification testSerum antibody testing using IF  <response>: Based on the clinical history, the most likely diagnosis is acute cervicitis and as gram stain does not show any organism so gonococcal infection is less likely; hence, Chlamydia trachomatis is the most likely organism. For C. trachomatis, investigation of choice and the most sensitive investigation is nucleic acid amplification test NAAT. Reference: Ananthanarayan and Paniker;s Textbook of Microbiology Tenth edition 