Basics
Description
Chlamydiae are obligate intracellular organisms classified as bacteria, but which possess qualities of both bacteria and viruses. They cause a variety of infections from the respiratory to the urogenital tract. The genus has been divided into Chlamydia (Chlamydia trachomatis, others) and Chlamydophila (Chlamydophila pneumoniae, Chlamydophila psittaci, others). Three species are known to affect humans:
- C. trachomatis: a leading cause of sexually transmitted infections in the United States, which can be vertically transmitted during childbirth
- C. pneumoniae: an important cause of respiratory infections in the school-aged child
- C. psittaci: a zoonosis, primarily an avian pathogen, causing the disease psittacosis in exposed humans
Epidemiology
- Spread person to person by respiratory droplets; no specific seasonality
- Asymptomatic carriage and prolonged nasopharyngeal shedding occurs.
- Peak ages of infection are 5-15 years.
- Coinfection with other respiratory pathogens is common.
- Serum antibodies are positive in about 50% of adults by age 20 years.
Risk Factors
School-aged children are at highest risk.
General Prevention
Cough etiquette (coughing into elbow or tissue) and proper hand hygiene are important control measures.
Pathophysiology
- Chlamydiae exist in two forms:
- Elementary body (EB): infectious form
- Reticulate body (RB): reproductive form
- Life cycle:
- EB is taken into cell by endocytosis and reorganizes into a RB to replicate.
- After replication, RB transformed to EB and are released by exocytosis or cytolysis.
- Cycle between endocytosis and release is 2-3 days, explaining need for prolonged treatment.
Diagnosis
History
- C. pneumoniae incubation period is approximately 21 days.
- Most commonly presents with prolonged cough (2-6 weeks), developing into atypical pneumonia
- Sore throat may precede onset of cough.
- Patients are mild to moderately ill; infection may be asymptomatic.
- Severe illness occurs in immunocompromised hosts.
Physical Exam
- Nasal discharge
- Nonexudative pharyngitis
- Laryngitis, otitis media, and sinusitis may be present.
- Lung exam may be notable for wheezing and rales.
Diagnostic Tests & Interpretation
Lab
- No FDA-approved, reliable PCR test available.
- Serologic testing and culture are available, but empiric treatment is recommended.
- Other lab findings are nonspecific including the following:
- Elevated liver enzymes
- Left-shifted CBC without neutrophilia
Imaging
Chest radiography
- May have focal or diffuse infiltrates
- Pleural effusion may occur.
Differential Diagnosis
- Atypical pneumonia due to Mycoplasma pneumoniae
- Viral pneumonia
- Influenza
- Parainfluenza
- Adenovirus
- Respiratory syncytial virus (RSV)
- Less frequently
- Coxiella burnetii
- Legionella pneumophila
Treatment
Medication (Drugs)
First-line therapy is recommended based on national guidelines, as antimicrobial therapy is usually initiated empirically when suspicion is high for atypical pathogens. Alternative therapies are targeted at C. pneumoniae.
- First line
- Azithromycin 10 mg/kg (max 500 mg) for 1 day followed by 5 mg/kg (max 250 mg) for 4 days
- In hospitalized patients, if clinical picture may also be consistent with typical pathogens, add ampicillin IV 150-200 mg/kg/24 h divided every 6 hours or amoxicillin 90 mg/kg/24 h divided every 12 hours (max 4,000 mg/day) if tolerating oral medications.
- Alternatives:
- If >8 years, doxycycline
- Levofloxacin if unable to tolerate macrolides
- Appropriate length of antimicrobial therapy in C. pneumoniae infections is unclear.
Ongoing Care
Prognosis
For C. pneumoniae, full recovery is expected in general.
Complications
Immunocompromised individuals including those with cystic fibrosis and sickle cell disease can experience a fulminant course.
Additional Reading
- Bradley JS, Byington CL, Shah SS, et al. The management of community-acquired pneumonia in infants and children older than 3 months of age: clinical practice guidelines. Clin Infect Dis. 2011;53(7):e25-e76. [View Abstract]
- Burillo A, Bouza E. Chlamydophila pneumoniae. Infect Dis Clin North Am. 2010;24(1):61-71. [View Abstract]
- Centers for Disease Control and Prevention. Sexually transmitted disease guidelines, 2010. MMWR Recomm Rep. 2010;59(RR-12):1-114. [View Abstract]
Codes
ICD09
- 079.88 Other specified chlamydial infection
ICD10
- A70 Chlamydia psittaci infections
SNOMED
- 429586004 Chlamydophila psittaci infection