What is Chlamydia?

Three Chlamydia species infect humans: C. trachomatis, C. pneumoniae and C. psittaci. C. trachomatis is the leading bacterial sexually transmitted infection, often asymptomatic but capable of causing pelvic inflammatory disease, infertility and neonatal infections. It also causes trachoma, a major source of preventable blindness. C. pneumoniae causes respiratory illnesses and may be linked to cardiovascular disease. Chlamydial infections occur worldwide, with trachoma concentrated in poorer regions. Globally, about 89 million new sexually transmitted cases arise annually.

By Robert Belland, David M. Ojcius & Gerald I. Byrne

https://www.nature.com/articles/nrmicro931

The numbers indicate WHO estimates of the prevalence of sexually transmitted Chlamydia infections among adults in 1999.