Chlamydophila pneumoniae or psittaci

Chlamydophila is a genus of bacteria in the Chlamydiaceae family that causes atypical pneumonias, which may become life threatening.

Epidemiology

Incidence – C. pneumophilia – 100/100,000 in U.S.
Age
- C. pneumoniae – peak incidence is late childhood to young adulthood
  - ~50% of young adults in the U.S. will have evidence of past infection by age 20
  - Reinfection throughout life is common
Transmission
- C. pneumoniae – respiratory secretions
  - May produce epidemics in close-quarter settings such as military barracks
- C. psittaci – respiratory inhalation during exposure to infected birds (zoonoses)
  - Does not require prolonged contact with infected bird
  - May be an occupation-related disease

Organism

C. psittaci and C. pneumoniae are obligate intracellular gram-negative bacteria

Clinical Presentation

C. pneumoniae
- Incubation – 7-10 days
- Constitutional – leukocytosis and fever are often lacking; may resemble Mycoplasma pneumoniae infections
- Pulmonary – bronchitis, pneumonia, exacerbations of chronic bronchitis and asthma
- Upper respiratory tract – laryngitis, otitis media, sinusitis, pharyngitis
- Dermatologic – erythema nodosum
- Neurologic – meningitis (uncommon)
- Cardiac – endocarditis, myocarditis (uncommon)
C. psittaci
- Incubation – 7-14 days
- Constitutional – fever, chills, headache, myalgias
- Pulmonary – cough, pleural rub, rales, dyspnea, pneumonia
- Gastrointestinal – diarrhea, nausea, anorexia, abdominal pain
- Hepatitic – hepatitis
- Dermatologic – faint macular rash may occur (Horder spots), erythema multiforme, erythema nodosum
- Neurologic – cranial nerve palsies, cerebellar involvement, transverse myelitis, meningitis
- Cardiac – endocarditis, myocarditis, pericarditis

Treatment

Antibiotic treatment is effective and curative

Indications for Testing

C. pneumoniae – atypical pneumonia presentation
C. psittaci – atypical pneumonia and a history of bird exposure

Laboratory Testing

Initial testing – CBC with differential
Serology
- Order serologies for C. pneumoniae, M. pneumoniae and Legionella pneumophila concurrently; routine diagnostic tests to identify etiologic agent of outpatient pneumonia in adults is optional (Infectious Disease Society of America/American Thoracic Society)
- Confirmed by paired serology for C. pneumoniae (four-fold elevation)
- Order antibody panel if suspicious of C. psittaci
- Performed using complement fixation, microimmunofluorescence, enzyme immunoassay
PCR – much more sensitive than culture; positive culture confirms diagnosis
Culture – difficult on atypical agents

Imaging Studies

Chest x-ray – no distinctive chest x-ray pattern

Differential Diagnosis

Respiratory tract infections
- Mycoplasma pneumoniae
- Legionella pneumophila
- Coxiella burnetii (Q-fever)
- Influenza virus
- Parainfluenza 1, 2, 3
- Hantavirus
- Respiratory syncytial virus (RSV)
- Bordetella pertussis (whooping cough)
- Adenovirus
Hepatitis – viral
Myocarditis
Myocardial infarction
Connective tissue disease
- Polymyositis
Erythema nodosum/erythema multiforme

Tests generally appear in the order most useful for common clinical situations

Test name: CBC with Platelet Count & Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count with Flow Cell Differential

Use:

May help to differentiate between bacterial and viral pneumonias

Test name: Chlamydia pneumoniae by PCR

ARUP #: 0060715

Methodology: Qualitative Polymerase Chain Reaction

Use:

Confirm C. pneumoniae as infectious agent in nasal wash, nasopharyngeal aspirate, bronchoalveolar lavage (BAL) or pleural fluid

More sensitive than IFA

Test name: Chlamydia Antibody Panel, IgG & IgM by IFA

ARUP #: 0065100

Methodology: Semi-Quantitative Indirect Fluorescent Antibody

Use:

Differentiate among Chlamydophila species (C. psittaci, C. pneumoniae)

Differentiate early IgM response to infection from persistent low-level titer

Because of cross-reactivity, a C. pneumoniae-specific reaction will exhibit titers two-fold or greater than C. trachomatis or C. psittaci serology

Limitations:

Anti-chlamydial IgM antibody is very cross-reactive and will often represent titers to multiple, non-infecting chlamydial species

Follow-up: If results are equivocal, retest sera 2-3 weeks after first test

Test name: Mycoplasma pneumoniae Antibodies Seroconversion Panel, IgG & IgM

ARUP #: 0050697

Methodology: Semi-Quantitative Enzyme Immunoassay

Use:

Testing to evaluate for acute Chlamydia infection

Because of cross-reactivity, a C. pneumoniae-specific reaction will exhibit titers two-fold or greater than C. trachomatis or C. psittaci serology

Test name: Legionella pneumophila Antigen, Urine

ARUP #: 0070322

Methodology: Qualitative Enzyme-Linked Immunosorbent Assay

Use:

Rapid diagnostic test for Legionella

Additional Tests Available

Test name: Chlamydia Antibody Panel, IgG by IFA

ARUP #: 0065139

Methodology: Semi-Quantitative Indirect Fluorescent Antibody

Comments:

Test name: Chlamydia Antibody Panel, IgM by IFA

ARUP #: 0065105