• Clinical science

Chlamydia infections


Chlamydiaceae is a family of gram-negative, obligate intracellular bacteria that includes 3 organisms pathogenic to humans: Chlamydia trachomatis, Chlamydophila pneumoniae, and Chlamydophila psittaci. C. trachomatis can be differentiated into serotypes A–C, D–K, and L1–L3. Serotypes A–C mainly affect the eyes and cause trachoma. An infection with serotypes D–K can result in genitourinary infections (e.g., vaginitis, PID, urethritis), conjunctivitis, and infant pneumonia. Serotypes L1–L3, in turn, lead to sexually transmitted lymphogranuloma venereum. While both C. pneumoniae and C. psittaci primarily affect the respiratory system, C. psittaci also causes psittacosis. Chlamydial infections are mostly diagnosed based on clinical presentation and are treated with doxycycline or macrolides. In all cases of sexually transmitted chlamydial infection, expedited partner therapy should also be initiated as soon as possible. All ocular manifestations are discussed in more detail in the “Conjunctivitis” article.


General characteristics

Life cycle

Elementary bodies survive in the Environment, Enter the cell via Endocytosis, and Evolve into reticulate bodies.

Reticulate bodies Replicate in the cell and Reorganize to elementary bodies.


Characteristics of Chlamydiaceae
Bacteria Serotypes Organ Transmission Disease
Chlamydia trachomatis A–C
  • Eyes
  • Smear infection via discharge from the eyes or nose of infected persons
  • Can be transmitted by direct contact, clothes, or insects
  • Eyes
  • Genitourinary tract
  • Lungs
  • Sexual intercourse
  • Vaginal birth (in which the mother is infected)
  • Sexual intercourse
Chlamydophila pneumoniae
  • Person-to-person transmission of respiratory secretions via aerosols
Chlamydophila psittaci
  • Airborne transmission (pathogens in the feces and dander of birds)

Chlamydial pneumonia

Infant pneumonia due to Chlamydia trachomatis (serotypes D–K)

  • Transmission: perinatal transmission during delivery via contact with the genital flora of an infected mother [4]
  • Incubation period: 4–12 weeks after delivery [5]
  • Clinical features [4]
  • Diagnostics [6]
  • Prevention: maternal screening and treatment before birth
  • Treatment: oral erythromycin; (drug of choice), azithromycin [4]
  • Complications: respiratory failure

Chlamydophila pneumoniae

Chlamydophila psittaci (psittacosis , "parrot fever" , or ornithosis ) [11]

Chlamydophila psittaci accumulates in parrots and other birds and causes atypical pneumonia.

Psittacosis is a notifiable disease and should be reported in most of the states.

Sexually transmitted infections

Chlamydial genitourinary infections

Lymphogranuloma venereum [22]

  • Pathogen: Chlamydia trachomatis serotypes L1–L3 (see “Sexually transmitted infections”)
  • Epidemiology
    • Most common in tropical and subtropical countries
    • Increasing incidence among men who have sex with men
  • Clinical features
    • Primary infection; (after approx. one week): small, painless genital ulcers (herpetiform) that heal spontaneously within a few days
    • Secondary infection; (after approx. 3 weeks): painful swelling of the lymph nodes in the inguinal region (buboes) with abscess formation (pus discharge) and systemic symptoms
  • Diagnostics: NAAT using swabs of the anogenital lesions, rectal mucosa, and/or lymph node specimens [23]
  • Treatment: doxycycline or erythromycin
  • Complications

C. trachomatis serotypes L1-L3 cause Lymphogranuloma venerum.

Lymphogranuloma venereum (pathogen: Chlamydia trachomatis serotypes L1–L3) should not be mistaken for granuloma inguinale or donovanosis (pathogen: Klebsiella granulomatis).