Coxiella burnetii - Q-Fever

Epidemiology

• Incidence – <50/year in U.S.
• Age – highest prevalence in 30s-60s
• Sex – M>F
  • Women and children more commonly asymptomatic
• Transmission
  • Main 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
    • Inhalation of contaminated dust particles and aerosols
    • Handling/ingestion of 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 – farming, veterinary medicine, abattoir work, military work
• Underlying valve disease – risk factor for endocarditis
• Ingestion of unpasteurized dairy products

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 second week of symptoms
• Chronic disease
  • Subsequent testing shows high levels of antibodies to phase I antigens and constant or decreasing levels of antibodies to phase II antigens
    • Because antibodies to phase I antigens generally require more time to appear, consistently 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%)
  • Defined as infection lasting >6 months
  • Presence of endocarditis – pathognomonic for chronic disease
  • Occurs in patients with preexisting 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 affected, resulting in hepatitis, vascular infection, osteomyelitis, lymphadenitis