Q Fever
Summary
Q fever is a zoonotic infection caused by Coxiella burnetii, an obligate intracellular bacterium. It is acquired primarily through inhalation of contaminated aerosols from farm animals, especially sheep, goats, and cattle during lambing/calving. Acute Q fever presents as a flu-like illness, atypical pneumonia, or hepatitis. Most cases are self-limiting, but a minority progress to chronic Q fever, which typically manifests as culture-negative endocarditis — a major diagnostic challenge. Treatment of acute disease is with doxycycline; Chronic Q fever requires prolonged combination therapy (doxycycline + hydroxychloroquine for ≥18 months).
Key Facts
- Organism: Coxiella burnetii (obligate intracellular)
- Source: Farm animals (sheep/goats especially during lambing)
- Transmission: Inhalation of contaminated aerosols
- Acute: Flu-like, Atypical pneumonia, Hepatitis
- Chronic: Culture-negative endocarditis (can occur years later)
- Treatment: Doxycycline (acute); Doxycycline + Hydroxychloroquine (chronic)
Clinical Pearls
"Q for Query": Named because the cause was initially unknown ("query fever").
"Lambing Season = Risk": Q fever outbreaks peak during lambing (spring). One infected placenta can infect people miles away.
"Culture-Negative Endocarditis": Q fever is a top cause. Always consider in BCNE.
"Hydroxychloroquine Makes Doxy Work": Hydroxychloroquine alkalinises the phagolysosome, allowing doxycycline to be effective against this intracellular organism.
Incidence
- Underdiagnosed (many mild cases)
- Outbreaks linked to farms
Geography
- Worldwide except New Zealand
- UK: Endemic, especially rural areas
Risk Groups
| Group | Notes |
|---|---|
| Farmers | Especially sheep/goat farmers |
| Vets | Occupational exposure |
| Abattoir workers | |
| Laboratory workers | Highly infectious |
| Visitors to farms | Especially during lambing |
Organism
- Coxiella burnetii
- Obligate intracellular
- Survives in environment (highly resistant)
Transmission
- Inhalation of aerosols from infected birth products, urine, faeces
- Can travel >1 km in wind
- Rarely: Ingestion (unpasteurised milk), Tick bite, Person-to-person (rare)
Pathogenesis
- Infects alveolar macrophages
- Survives in phagolysosome (acidophilic)
- Spreads haematogenously
- Chronic infection: Persists in heart valves, vascular grafts
Acute Q Fever (60% have symptoms)
| Feature | Notes |
|---|---|
| Flu-like illness | Fever, Headache, Myalgia |
| Atypical pneumonia | Cough, CXR infiltrates |
| Hepatitis | Elevated transaminases |
| Asymptomatic | 40% |
Chronic Q Fever (<5%)
| Feature | Notes |
|---|---|
| Endocarditis | Culture-negative; On prosthetic or abnormal valves |
| Vascular graft infection | |
| Osteomyelitis | |
| Hepatitis | Granulomatous |
At-Risk for Chronic
| Factor | Risk |
|---|---|
| Pre-existing valve disease | High |
| Prosthetic valve | Very high |
| Vascular graft | |
| Pregnancy | Fetal loss, Chronic infection |
| Immunosuppression |
Acute
- Fever
- Hepatomegaly (hepatitis)
- Lung signs (pneumonia)
Chronic (Endocarditis)
- Fever of unknown origin
- New/changing murmur
- Splenomegaly
- Osler nodes, Janeway lesions (rare)
Serology (Diagnosis)
| Test | Notes |
|---|---|
| Phase II IgG | Acute infection (>00 indicates recent infection) |
| Phase I IgG | Chronic infection (>00 indicates chronic Q fever) |
Other
| Test | Findings |
|---|---|
| LFTs | Raised transaminases |
| CXR | Patchy infiltrates (pneumonia) |
| Blood cultures | NEGATIVE (organism cannot be cultured routinely) |
| Echo | Vegetations (endocarditis) |
| PCR | Tissue or blood |
Treatment Approach
┌──────────────────────────────────────────────────────────┐
│ Q FEVER MANAGEMENT │
├──────────────────────────────────────────────────────────┤
│ │
│ ACUTE Q FEVER: │
│ • Doxycycline 100mg BD for 14 days │
│ • Alternative: Azithromycin, Fluoroquinolones │
│ • Most recover without treatment, but Doxycycline │
│ shortens illness and may prevent chronic infection │
│ │
│ CHRONIC Q FEVER (Endocarditis): │
│ • Doxycycline 100mg BD + Hydroxychloroquine 200mg TDS │
│ • Duration: ≥18 months (often longer) │
│ • Hydroxychloroquine alkalinises phagolysosome, │
│ allowing Doxycycline to work intracellularly │
│ • Regular monitoring: Serology, Eye checks (HCQ toxicity│
│ │
│ PREGNANCY: │
│ • Co-trimoxazole throughout pregnancy │
│ • Doxycycline + HCQ postpartum │
│ • High risk of fetal loss and chronic infection │
│ │
│ PREVENTION: │
│ • Restrict access to lambing areas │
│ • PPE for farmers/vets │
│ • Pasteurise milk │
│ • Vaccine available in Australia │
│ │
└──────────────────────────────────────────────────────────┘
Acute
- Meningitis (rare)
- Myocarditis
- Acute hepatitis
Chronic
- Culture-negative endocarditis
- Vascular graft infection
- Osteomyelitis
- Death (if untreated)
Acute
- Most recover fully (with or without treatment)
Chronic
- High mortality if untreated (up to 60%)
- Good outcomes with prolonged treatment
Key Resources
- CDC: Q Fever Information
- PHE: Q Fever Guidance
Key Evidence
Doxycycline + Hydroxychloroquine
- Reduces mortality in chronic Q fever
- Duration ≥18 months
What is Q Fever?
Q fever is an infection caused by bacteria called Coxiella burnetii. It is spread by breathing in dust contaminated by farm animals, especially sheep and goats during lambing.
What Are the Symptoms?
Most people have a flu-like illness with fever, headache, and muscle aches. Some develop a cough or liver problems.
Is It Serious?
Usually not. Most people recover. However, a small number develop a long-term (chronic) form that can cause heart valve infection (endocarditis).
How is It Treated?
- Acute: Antibiotics (doxycycline) for 2 weeks
- Chronic: Long-term antibiotics (18+ months)
Who is at Risk?
- Farmers, vets, and people who work with livestock
- Pregnant women (higher risk of complications)
Primary Resources
- CDC. Q Fever. cdc.gov/qfever
Key Studies
- Raoult D, et al. Treatment of Q fever endocarditis. Arch Intern Med. 1999;159(2):167-173. PMID: 9927100