Q Fever

Q fever, caused by Coxiella burnetii, is a bacterial zoonosis with a wide clinical spectrum that can be life-threatening and, in some cases, can become chronic.

Epidemiology

In recent years in Europe, there has been an increase in the number of reported cases. In the Netherlands in particular, between 2007 and 2010 there were more than 4,000 cases reported.

Clinical description

Q fever affects all ages, but is mostly reported in those aged 30-70 years. The incubation period is 2-3 weeks. Approximately 60% of cases are asymptomatic. The most common symptoms of acute Q fever are high fever, severe headache, myalgia, chills, and cough. It may also be associated with pneumonia or hepatitis. Pneumopathy is mostly moderate but pleural effusion or acute respiratory distress may occur. Symptoms may last 10-90 days. Rarely, patients may have neurological (ex. meningitis), cardiac (pericarditis, myocarditis) or dermatological manifestations (maculopapular eruption, erythema nodosum). Children often suffer from gastrointestinal manifestations and skin rash (in up to 50% of diagnosed children). The infection may evolve to a chronic form (<5% of cases) in persons with a predisposition (ex. heart valve or vascular defect), months or years after initial infection. Chronic manifestations include endocarditis, vascular infections and osteomyelitis, or less commonly, fever with hepatitis evolving to hepatic fibrosis or cirrhosis. During pregnancy, a primary infection may cause spontaneous abortion, prematurity, low birth weight, fetus infection or recurrent miscarriages. Chronic Q fever after delivery may be associated with cardiac involvement.

Etiology

Coxiella burnetii, is an intracellular gram-negative bacterium now classified in the gamma group of Proteobacteria. Most infections are due to inhalation of aerosols or dust contaminated with dried birth fluids or excreta from infected animals. Less frequent routes of infection include ingesting contaminated milk, tick bite, or fomite transmission. Person-to-person and mother-to-fetus transmission has been reported.

Diagnostic methods

Diagnosis of acute Q fever is confirmed by serologic evidence of a fourfold increase in phase II immunoglobulin (Ig) G via an immunofluorescent assay test between paired sera taken 3-6 weeks apart. PCR testing on blood or serum may be useful in the first 2 weeks of symptom onset and before antibiotic administration. A single high serum phase II IgG titer in the convalescent stage may be considered as evidence of probable infection. Confirmation of chronic Q fever is based on an increasing phase 1 IgG titer (typically ≥1:1024) and an identifiable nidus of infection (e.g., endocarditis, vascular infection, osteomyelitis, chronic hepatitis). Liver enzyme levels are commonly increased.

Differential diagnosis

Differential diagnosis includes any disease with fever and other constitutional symptoms such as Brucellosis (see this term) and influenza.

Management and treatment

Prophylactic strategies are based on vaccination (in Australia) and appropriate hygiene measures. Adherence to standard precautions during care of patients prevents transmission. Symptomatic patients with acute Q fever should be treated for 2 weeks with doxycycline. A pregnancy test should be performed before commencing treatment in women of child-bearing age. Children aged younger than 8 with mild illness, pregnant women, and patients allergic to doxycycline can be treated with trimethoprim-sulfamethoxazole. Chronic Q fever is treated with a combination of doxycycline and hydroxychloroquine for a minimum of 18 months.

Prognosis

Acute Q fever is often a mild or self-limiting illness with a low risk for death. Untreated chronic Q fever endocarditis or vascular infection is often fatal. In treated patients with chronic Q fever endocarditis, the 10-year mortality rate is 19%.