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, , 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.
- Gram-negative organisms, that Gram stain poorly
- Obligate intracellular bacteria (unable to produce its own ATP)
- Absent peptidoglycan () in the cell wall, which makes beta-lactam antibiotics ineffective
- Visible as cytoplasmic inclusion bodies on Giemsa stain or fluorescent antibody-stained smear
- Very difficult cultivation
- First phase: elementary bodies (small and dense bodies that characterize the infectious stage of Chlamydiaceae; stable in the extracellular environment and almost inactive metabolically) 
- Second phase: reticulate bodies (represent the obligate intracellular, replicative, and metabolically active form of Chlamydiaceae)
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|
|Chlamydia trachomatis||A–C|| || |
|D–K|| || |
|L1–L3|| || || |
|Chlamydophila pneumoniae|| || |
|Chlamydophila psittaci|| |
Infant pneumonia due to Chlamydia trachomatis (serotypes D–K)
- Transmission: perinatal transmission during delivery via contact with the genital flora of an infected mother 
- Incubation period: 4–12 weeks after delivery 
- Clinical features 
- Diagnostics 
- Prevention: maternal screening and treatment before birth
- Treatment: oral erythromycin; (drug of choice), azithromycin 
- Complications: respiratory failure
- Transmission: person-to-person transmission of respiratory secretions via aerosols 
- Incubation period: 3–4 weeks
- Clinical features
- Diagnostics 
- Complications 
Chlamydophila psittaci (psittacosis , "parrot fever" , or ornithosis ) 
- Airborne; (pathogens from feces and/or dander of infected birds)
- Mainly affects individuals in contact with free-ranging birds or pets, or occurs as an occupational disease
- Incubation period: 5–14 days 
- Clinical features: Symptoms can vary greatly.
- Culture of respiratory specimens (e.g., sputum, pleural fluid)
- Polymerase chain reaction (PCR) of respiratory specimens
- Serology for Chlamydophila psittaci IgG and IgM with the complement-fixation test (CFT) or micro-immunofluorescence (MIF); diagnosis requires either of the following:
- Complications 
Chlamydophila psittaci accumulates in parrots and other birds and causes atypical pneumonia.
Sexually transmitted infections
Chlamydial genitourinary infections
- Pathogen: Chlamydia trachomatis serotypes D–K (see “”)
- Types of infections
- The majority of infected individuals are asymptomatic, which leads to a delay in seeking treatment, and thus increases the risk of disease transmission.
- (Muco)purulent vaginal discharge; and/or intermenstrual/postcoital bleeding
- Possible dysuria, pollakiuria, polyuria, dyspareunia
- See “ ” for more information.
- NAAT: gold standard
- Antigen detection
- Other diagnostic tests 
- Culture: rarely used nowadays
- Serology: may be helpful in the diagnosis of chronic and invasive infections; not performed routinely
- Azithromycin or doxycycline 
- Expedited partner therapy is recommended in most cases of STIs, particularly chlamydia and gonorrhea.
- Asymptomatic patients should also be treated to prevent serious complications (e.g., PID and infertility) and further spreading. 
- Screening for chlamydia (USPSTF recommendations)
Lymphogranuloma venereum 
- Pathogen: Chlamydia trachomatis serotypes L1–L3 (see “”)
- 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 
- Treatment: doxycycline or erythromycin
C. trachomatis serotypes L1-L3 cause Lymphogranuloma venerum.