Chlamydia in the U.S.: First Reported Cases (1938)

The first documented cases of Chlamydia trachomatis infection in the United States were identified in California and Colorado in 1938 by Dr. T.E. McGibbon. At the time, the organism was classified as a virus (known as "TRIC agent" or "PLT agent"); its bacterial nature was confirmed in the 1960s.

Chlamydia became a nationally notifiable disease in 1984. Today, it is the most commonly reported bacterial STI in the U.S., with over 1.6 million cases reported annually (CDC), though actual incidence is estimated to be 2–3 times higher due to asymptomatic infections.

Key milestones: introduction of nucleic acid amplification tests (NAATs) in the 1990s revolutionized screening; single-dose azithromycin (1990s) simplified treatment; expedited partner therapy (EPT) expanded in 2000s.