Chlamydia infections

Last updated: September 15, 2023

Summarytoggle arrow icon

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., cervicitis, 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. Ocular manifestations are discussed in more detail in the “Bacterial conjunctivitis” and “Neonatal conjunctivitis” articles.

Generaltoggle arrow icon

General characteristics

Life cycle

  • First phase: elementary bodies (small and dense bodies that characterize the infectious stage of Chlamydiaceae; stable in the extracellular environment and almost inactive metabolically) [1]
    1. Attachment of extracellular elementary bodies to target cells (mostly on the respiratory or urogenital epithelium)
    2. Endocytosis
    3. Transformation into reticulate bodies in the endosome
  • Second phase: reticulate bodies (represent the obligate intracellular, replicative, and metabolically active form of Chlamydiaceae)
    1. Replication by fission and aggregation of various reticulate bodies in the endosome (at which point they are called inclusion bodies)
    2. Transformation of reticulate bodies into elementary bodies
    3. Lysis of endosomes
    4. Release of newly formed elementary bodies and exit from cell
    5. New start of 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

Chlamydial pneumoniatoggle arrow icon

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

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 infectionstoggle arrow icon

Chlamydia trachomatis predominantly affects the genitourinary tract although it can cause pneumonia and neonatal conjunctivitis in infants born vaginally to infected mothers. Disease presentation depends on the serotype involved. Serotypes D–K cause genitourinary chlamydia (nonlymphogranuloma venereum), which presents with urethritis, proctitis, cervicitis, pelvic inflammatory disease, epididymitis, and prostatitis; serotypes L1–L3 cause lymphogranuloma venereum, which presents with either rectal infection (proctitis) or ulceration and inguinal lymphadenopathy.

Genitourinary chlamydia (Nonlymphogranuloma venereum)toggle arrow icon



Clinical features [17]

Perinatal transmission can cause neonatal chlamydial conjunctivitis or infant pneumonia due to C. trachomatis.

Diagnostics of genitourinary chlamydia [16]

  • Preferred test: Nucleic Acid Amplification Test (NAAT)
    • Detects Chlamydia trachomatis RNA or DNA, e.g., by PCR [15]
    • Specimen collection: [16]
      • Individuals with female genitalia: vaginal swab (preferred), cervical swab, or first-void urine
      • Individuals with male genitalia: first-void urine (preferred) or urethral swab
      • Suspected exposure from rectal intercourse: rectal swab
  • Other diagnostic tests: not routinely recommended; a culture may be preferred over NAAT in select circumstances. [18]

Management of genitourinary chlamydia [16]


Doxycycline is contraindicated in pregnancy; pregnant patients should be treated with azithromycin. [16]

Consider child sexual abuse and human trafficking in adolescents presenting with genitourinary chlamydia.

Antibiotic therapy

Patients with gonorrhea coinfection should be treated with oral doxycycline plus a single dose of intramuscular ceftriaxone. [16]

If nonadherence to treatment is a concern, directly observed therapy with azithromycin (given as a single dose) is preferred. [16]

Follow-up [16]

  • Follow-up of pregnant patients with chlamydia
  • Follow-up of nonpregnant patients with chlamydia
    • Consider retesting at 4 weeks if any of the following are present:
      • Persistent symptoms
      • Concern for reinfection
      • Concern for poor adherence to treatment regimen
    • Otherwise, retest at 3 months.

Complications [16][18]

Screening for chlamydia [15][16]

Screen patients using NAAT.

Recommended screening for chlamydia [16]
Frequency Specimen collection
Sexually active women
  • Annual screening for patients: [15][16]
  • Preferred: vaginal swab
  • Alternative: cervical swab, or first-void urine
  • Patients with a history of anal sex: A rectal swab should be additionally obtained.
Prenatal screening for Chlamydia trachomatis
Sexually active young men
  • No recommended set intervals
  • Consider screening in clinical settings with a high prevalence of chlamydial infections. [16]
  • Preferred: first-void urine
  • Alternative: urethral swab
  • Obtain samples from sites of potential exposure in the last year (except oropharyngeal), in patients with a history of: [16]
    • Insertive intercourse: first-void urine (preferred) or urethral swab
    • Receptive anal intercourse: rectal swab

Best practices for screening transgender individuals have not been established; tailor screening to the patient's anatomy. See also “Principles of transgender health care.” [16][17]

Screening is typically performed simultaneously with screening for gonorrhea.

Lymphogranuloma venereumtoggle arrow icon

Etiology [16]

C. trachomatis serotypes L1-L3 cause Lymphogranuloma venereum.


  • Globally: more common in tropical and subtropical regions [19]
  • In high-income countries: increasing incidence among MSM [22]

Clinical features [16][19]

  • Rectal infection (most common): proctitis or proctocolitis
    • ∼ 50% of cases may be asymptomatic or mild. [22]
    • Mild symptoms: constipation, mucous streaking of stool [23]
    • Severe symptoms: rectal pain, bleeding, and discharge; tenesmus, and systemic symptoms [16]
  • Genital or anal infection: genital and inguinal disease [19]
    • Primary infection (after approx. 1 week)
      • Small, painless genital ulcers (herpetiform) that heal spontaneously within a few days
      • May be accompanied by mucopurulent discharge
    • Secondary infection (2–6 weeks after onset of primary infection)
  • Oral infection: oral ulceration, which may be followed by cervical lymphadenopathy [16]

Ulcers may have healed by the time patients present with painful lymphadenopathy. [16]

Diagnostics [16]

If clinical suspicion for LGV is high, start antibiotic treatment immediately rather than waiting for the results of diagnostic testing. [16]

Management [16]


Antibiotic therapy [16]

Bubo drainage [16][19]

Follow-up [16]

  • Regularly reassess the patient until signs and symptoms have resolved.
  • Retest for C. trachomatis after completion of treatment.
    • Pregnant women: at 4 weeks
    • Other patients: at 3 months (up to 12 months, if necessary) [16]

Differential diagnoses of LGV

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

Complications [16][19]

Complications represent a tertiary stage of the disease. [19]

Referencestoggle arrow icon

  1. Pammi M, Hammerschlag MR. Chlamydia trachomatis infections in the newborn. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. Last updated: September 21, 2016. Accessed: September 25, 2016.
  2. Falkow S, Rosenberg E, Schleifer K-H, Stackebrandt E. The Prokaryotes: Vol. 7: Proteobacteria: Delta and Epsilon Subclasses. Deeply Rooting Bacteria. Springer Science & Business Media ; 2006: p. 749
  3. Chlamydial Infections - 2015 Sexually Transmitted Diseases Treatment Guidelines. . Accessed: June 19, 2020.
  4. Mishra K, Bhardwaj P, Mishra A, Kaushik A. Acute Chlamydia trachomatis respiratory infection in Infants. Journal of Global Infectious Diseases. 2011; 3 (3): p.216.doi: 10.4103/0974-777x.83525 . | Open in Read by QxMD
  5. Chlamydia pneumoniae Infection. Updated: February 7, 2014. Accessed: September 25, 2016.
  6. Zaleznik DF. Pneumonia caused by Chlamydia pneumoniae in adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. Last updated: May 3, 2016. Accessed: September 25, 2016.
  7. Baron EJ, Miller JM, Weinstein MP, et al. A Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2013 Recommendations by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM)a. Clinical Infectious Diseases. 2013; 57 (4): p.e22-e121.doi: 10.1093/cid/cit278 . | Open in Read by QxMD
  8. Psittacosis. Updated: July 7, 2016. Accessed: September 25, 2016.
  9. Balsamo G, Maxted AM, Midla JW, et al. Compendium of Measures to ControlChlamydia psittaciInfection Among Humans (Psittacosis) and Pet Birds (Avian Chlamydiosis), 2017. J Avian Med Surg. 2017; 31 (3): p.262-282.doi: 10.1647/217-265 . | Open in Read by QxMD
  10. Stewardson AJ, Grayson ML. Psittacosis. Infect Dis Clin North Am. 2010; 24 (1): p.7-25.doi: 10.1016/j.idc.2009.10.003 . | Open in Read by QxMD
  11. Stanberry LR, Bernstein DI. Sexually Transmitted Diseases. Academic Press ; 2000
  12. Bentaleb I, Abdelghani KB, Rostom S, Amine B, Laatar A, Bahiri R. Reactive Arthritis: Update. Curr Clin Micro Rpt. 2020; 7 (4): p.124-132.doi: 10.1007/s40588-020-00152-6 . | Open in Read by QxMD
  13. Hammerschlag MR, Kohlhoff SA, Gaydos CA. Chlamydia pneumoniae. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 2015: p.2174-2182.e2.doi: 10.1016/b978-1-4557-4801-3.00184-3 . | Open in Read by QxMD
  14. Faris R, Andersen SE, McCullough A, Gourronc F, Klingelhutz AJ, Weber MM. Chlamydia trachomatis Serovars Drive Differential Production of Proinflammatory Cytokines and Chemokines Depending on the Type of Cell Infected. Front Cell Infect Microbiol. 2019; 9.doi: 10.3389/fcimb.2019.00399 . | Open in Read by QxMD
  15. Davidson KW, Barry MJ, et al. Screening for Chlamydia and Gonorrhea. JAMA. 2021; 326 (10): p.949.doi: 10.1001/jama.2021.14081 . | Open in Read by QxMD
  16. Workowski KA, Bachmann LH, Chan PA, et al. Sexually Transmitted Infections Treatment Guidelines, 2021. MMWR. Recommendations and Reports. 2021; 70 (4): p.1-187.doi: 10.15585/mmwr.rr7004a1 . | Open in Read by QxMD
  17. Yonke N, Aragón M, Phillips JK. Chlamydial and Gonococcal Infections: Screening, Diagnosis, and Treatment. Am Fam Physician. 2022; 105 (4): p.388-396.
  18. Centers for Disease Control and Prevention.. Recommendations for the laboratory-based detection of Chlamydia trachomatis and Neisseria gonorrhoeae 2014. MMWR Recomm Rep. 2014; 63 (RR-02): p.1-19.
  19. de Vries HJC, de Barbeyrac B, de Vrieze NHN, et al. 2019 European guideline on the management of lymphogranuloma venereum. J Eur Acad Dermatol Venereol. 2019; 33 (10): p.1821-1828.doi: 10.1111/jdv.15729 . | Open in Read by QxMD
  20. Reporting and Confidentiality. Updated: July 22, 2021. Accessed: June 17, 2022.
  21. AAP Committee on Infectious Diseases. Red Book: 2021–2024 Report of the Committee on Infectious Diseases. American Academy of Pediatrics ; 2021
  22. Williamson DA, Chen MY. Emerging and Reemerging Sexually Transmitted Infections. N Engl J Med. 2020; 382 (21): p.2023-2032.doi: 10.1056/nejmra1907194 . | Open in Read by QxMD
  23. Vries HJC, Nori AV, Kiellberg Larsen H, et al. 2021 European Guideline on the management of proctitis, proctocolitis and enteritis caused by sexually transmissible pathogens. J Eur Acad Dermatol Venereol. 2021; 35 (7): p.1434-1443.doi: 10.1111/jdv.17269 . | Open in Read by QxMD
  24. Stoner BP, Cohen SE. Lymphogranuloma Venereum 2015: Clinical Presentation, Diagnosis, and Treatment. Clin Infect Dis. 2015; 61 (suppl 8): p.S865-S873.doi: 10.1093/cid/civ756 . | Open in Read by QxMD

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