Can Q fever cause pneumonia?

Q Fever Pneumonia

Yes, Q fever definitively causes pneumonia and is an important, underrecognized cause of community-acquired pneumonia that should be considered in patients presenting with fever, severe headache, and nonproductive cough, particularly those with livestock exposure or residence in rural areas. 1

Clinical Significance

Pneumonia is one of the three cardinal manifestations of acute Q fever, occurring alongside nonspecific febrile illness and hepatitis after a 2-3 week incubation period. 1 The CDC guidelines emphasize that Coxiella burnetii may be an underrecognized cause of community-acquired pneumonia, with historical data showing Q fever accounted for 2.3% of hospitalized community-acquired pneumonia cases in North America. 1

Key Clinical Features to Recognize Q Fever Pneumonia

Cardinal Symptoms

• Fever lasting a median of 10 days untreated (range 5-57 days), with most cases defervescing within 72 hours of doxycycline treatment 1
• Severe, debilitating headache that may be retroorbital with photophobia or radiate to the jaw, sometimes misdiagnosed as migraine or dental infection 1, 2
• Nonproductive cough present in approximately 50% of patients, though cough may be absent despite radiographic pneumonia 1
• Myalgia and fatigue among the most frequently reported symptoms 1, 2

Distinguishing Characteristics

• Upper respiratory signs are notably absent in Q fever pneumonia compared to other etiologies 1
• Normal white blood cell count despite significant illness 3
• Elevated liver enzymes in approximately 45% of cases, even when hepatitis is not the primary manifestation 3

Important Caveat

Q fever pneumonia cannot be distinguished clinically, radiologically, or by routine laboratory evaluation from other causes of community-acquired pneumonia, making serologic testing essential for diagnosis. 1

Epidemiologic Risk Factors

Consider Q fever pneumonia in patients with:

• Livestock exposure, particularly cattle, sheep, or goats, especially during parturition 1
• Rural residence or living within 10 miles of a farm 1, 2
• Occupational animal contact (veterinarians, farmers, slaughterhouse workers) 1

Critical Pitfall

Absence of direct animal contact should NOT exclude Q fever from consideration, as airborne transmission can occur over considerable distances, and 60% of reported U.S. cases occur in patients without reported livestock contact. 1

Diagnostic Approach

Serologic Testing (Gold Standard)

• Paired serum samples showing fourfold change in IgG antibody titer to C. burnetii phase II antigen by immunofluorescence assay 2
• Single IgG titer ≥1:128 to phase II antigen in a patient ill >1 week indicates probable acute infection 2

PCR Testing

• Perform on whole blood or serum during the first 2 weeks of symptoms for early diagnosis 2

Treatment Recommendations

First-Line Therapy

Doxycycline is the treatment of choice for Q fever pneumonia, as explicitly indicated in FDA labeling for Q fever caused by Rickettsiae. 4 The standard regimen is doxycycline 100 mg twice daily for 10 days. 5

Evidence Supporting Doxycycline

• Superior to erythromycin with faster fever reduction (3 days vs 4.3 days) and significantly fewer side effects (2 patients vs 11 patients, p<0.01) 5
• Early treatment within the first 3 days of symptoms is most effective, and treatment should not be delayed while awaiting laboratory confirmation if Q fever is strongly suspected 2

Treatment Response

The majority of cases defervesce within 72 hours of doxycycline administration, providing a useful clinical marker of appropriate therapy. 1

Clinical Course and Prognosis

• Mortality is <2% in acute Q fever, making it generally a self-limited disease 1
• Radiographic resolution occurs in nearly all patients by day 40 of illness 5
• Age affects fever duration: 60% of patients >40 years have fever lasting >14 days compared to 29% of patients <40 years 1

Special Populations

Children

• Q fever pneumonia is usually moderate with mild cough in children 1
• Children have milder illness than adults and are less likely to be symptomatic 1
• Rash is more common in children (up to 50%) compared to adults (5-21%) 1

Pregnant Women

• May be less likely to have symptoms compared to other adults 1
• Require antibiotic treatment if infected during pregnancy due to risk of adverse pregnancy outcomes 1

Risk of Chronic Disease

<5% of acute Q fever patients develop chronic disease, most commonly endocarditis in patients with pre-existing valvular disease, vascular grafts, or arterial aneurysms. 1 Patients with these risk factors require clinical assessment and consideration for prolonged follow-up after acute infection. 1