Chlamydia beyond the genital tract: a major contributor to community-acquired pneumonia

Chlamydial pneumonia is a respiratory infection caused by three distinct species of obligate intracellular pathogens that include Chlamydia pneumoniae, C. psittaci, and C. trachomatis. Although they differ morphologically and are transmitted by distinct routes, all three organisms can elicit a complex clinical spectrum that ranges from acute pneumonia to chronic inflammation and extrapulmonary disease. Globally, chlamydial pneumonia represents a significant proportion of community-acquired pneumonia (CAP) cases, with species-specific prevalence varying by population and diagnostic method. However, diagnosis can be challenging due to the non-specific nature of its clinical presentation. Although serological testing is available for laboratory diagnosis, empirical antibiotic therapy based on clinical assessment is often sufficient for cure. The clinical course is generally mild, and the disease responds well to appropriate antibiotic treatment. This review summarizes the etiology, epidemiology, pathogenesis, and clinical manifestations of chlamydial pneumonia. We critically evaluate current diagnostic and therapeutic approaches, and discuss the associated public health burden. By synthesizing the latest evidence across these domains, this analysis aims to advance scientific understanding and provide a robust foundation for optimizing prevention, diagnostic accuracy, and therapeutic strategies against these complex infections.