Sex Transm Dis 48 (9): e122-e123, 2021. doi: 10.1097/OLQ.0000000000001344 Diagnosis of Chlamydia For C trachomatis, nucleic acid-based testing For C pneumoniae, culture or nucleic acid-based testing For C psittaci, serologic tests or polymerase chain reaction (PCR; where available) (See also the CDC's 2021 Sexually Transmitted Infections Treatment Guidelines: Chlamydial Infections.)