Q-Fever - Coxiella burnetii

Diagnosis

Indications for Testing

• Flu-like illness with appropriate risk factors
• Presence of blood culture-negative endocarditis

Laboratory Testing

• CDC laboratory confirmation of C. burnetii
• Nonspecific testing – acute disease
  • CBC – 25% have thrombocytopenia
  • Serum transaminases – moderately elevated in many patients
  • Patients with endocarditis
    • Sedimentation rate, C-reactive protein – elevated
    • CBC – anemia, thrombocytopenia
    • Urinalysis – hematuria
• Antibody titers by IFA, ELISA
  • Acute disease
    • Phases I and II – IgM increased
    • Phase II, IgG increased
    • May take 2-4 weeks after onset of symptoms to rise
    • May be detected up to 12 weeks after illness onset
  • Chronic disease
    • Phase I – IgG persistently increased
    • Endocarditis – IgG titer ≥1:800 is diagnostic 
• PCR – helpful in patients where disease is suspected and titers are low
• Immunohistochemical staining – not widely available
• Culture tests – not recommended
  • Lack sensitivity
  • Available only in research laboratories

Imaging Studies

• Echocardiogram

Monitoring

Clinical Background

Q-fever, a worldwide zoonosis, is caused by Coxiella burnetii and is named for a 1985 disease outbreak in Queensland, Australia.

Epidemiology

• Incidence – <50/year in U.S.
• Age – highest prevalence in 30s-60s
• Sex – M>F
  • Women and children more commonly asymptomatic
• Transmission
  • Important reservoirs of C. burnetii include cattle, sheep, and goats, as well as the rodents, cats, and birds that feed on them
  • Infection in these animals is enzootic and usually asymptomatic
  • Bacteria infects humans via
    • Inhaling contaminated dust particles and aerosols
    • Handling/ingesting infected raw meat or milk

Organism

• Gram-negative coccobacillus
• Obligate intracellular bacterial pathogen (family Coxiellaceae; order Legionellales) with worldwide distribution
• Classified as a class B bioterrorism agent

Risk Factors

• Occupational – farmers, veterinarians, abattoir workers, military personnel
• Ingestion of unpasteurized dairy products
• Underlying valve disease – risk factor for endocarditis

Pathophysiology

• C. burnetii exists in two antigenic phases (phases I and II) – antigenic difference is important to diagnosis
  • Antibodies to both phase I and II antigens may persist for months or years after initial infection
• Acute disease
  • Antibody levels to phase II antigens are usually higher (often by several orders of magnitude) than those for phase I antigens and are usually detected during the second week of symptoms
• Chronic disease
  • Subsequent testing shows high antibody levels to phase I antigens and constant or decreasing levels of antibodies to phase II antigens
    • Because antibodies to phase I antigens generally require longer to appear, consistent high levels may indicate continued exposure to the bacteria
  • Signs and symptoms of inflammatory disease

Clinical Presentation

• Incubation period – ~2-6 weeks
• Acute disease symptoms
  • Most cases are self-limiting, flu-like illnesses
    • Fever peaks in 2-4 days near 40°C, then gradually declines over period of 1-2 weeks
  • Constitutional – malaise, anorexia, myalgias, weakness, intense headache
  • Pneumonia or bronchitis – tachypnea, rales, rhonchi, cough, wheezing
  • Hepatitis – nausea, vomiting, diarrhea, anorexia, elevated transaminases, rarely jaundice
  • Myocarditis, pericarditis
  • During pregnancy – abortion, prematurity, low birth weight
• Chronic disease symptoms – rare (<1%)
  • Presence of endocarditis – pathognomonic for chronic disease
    • Occurs in patients with pre-existing heart valve damage (usually aortic and mitral valves), immunosuppression, or chronic renal disease
    • May result in culture-negative endocarditis
    • Symptoms – low-grade fever, cardiac failure, hepatosplenomegaly, clubbing of digits
  • Other organs may be involved – hepatitis, vascular infection, osteomyelitis, lymphadenitis

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Click the plus sign to expand the table of additional tests.

Test Name and Number	Comments
Antimicrobial Susceptibility - Bactericidal Assay 0060204 Method: Broth Microdilution
Coxiella burnetii (Q-Fever) Antibody IgG, Phase II by IFA 0050464 Method: Semi-Quantitative Indirect Fluorescent Antibody