Print
Clinical Features
Following the usual incubation period of 2-14 days, Q fever generally occurs as a fever illness lasting 2 days to 2 weeks. The incubation period varies according to the numbers of organisms inhaled, with longer periods between exposure and illness with lower numbers of inhaled organisms (up to forty days in some cases).
The disease appears as an acute non-differentiated febrile illness, with headaches, fatigue, and muscle aches are prominent symptoms. Physical examination of the chest usually reveals no abnormalities. Pneumonia, manifested by an abnormal chest x-ray, occurs in half of all patients, but only around half of these, or 28% of patients, will have a dry cough. Chest pain occurs in about one-fourth of patients with Q fever pneumonia. Chest radiograph abnormalities, when present, are patchy infiltrates that may resemble viral or mycoplasma pneumonia. Rounded opacities and glandular disease have also been described.
Approximately 33% of Q fever cases will develop acute hepatitis. This can appear with fever and abnormal liver function tests with the absence of pulmonary signs and symptoms. Uncommon complications include chronic hepatitis, culture-negative endocarditis, aseptic meningitis, encephalitis and osteomyelitis. Most patients who develop heart inflammation have pre-existing valvular heart disease.
Diagnosis
Q fever usually appears as a non-specific fever illness, or a primary atypical pneumonia, it may be difficult to distinguish from viral illnesses and must be differentiated from pneumonia caused by Mycoplasma pneumonia, Legionella pneumophila, Chlamydia psittaci, and Chlamydia pneumonia (TWAR). More rapidly progressive forms of Q fever pneumonia may look like bacterial pneumonias such as tularemia or plague. Significant numbers of casualties (from the same geographic area) appearing over a one to two week period with a nonspecific fever illness, and associated pulmonary symptoms in about a quarter of cases, may indicate the possibility of an attack with aerosolized Q fever. The final diagnosis will depend on the clinical and epidemiologic picture in the context of a possible bioterrorism attack.
Laboratory Diagnosis
An abnormal increase in the number of white blood cells may be present in one third of those infected. Most patients with Q fever have a mild elevation of liver enzymes levels. Isolation of the organism is impractical, as the organism is difficult to culture and a significant hazard to laboratory workers.
Medical Management
Standard Precautions are recommended for healthcare workers. Most cases of acute Q fever will eventually resolve without antibiotic treatment, but all suspected cases of Q fever should be treated to reduce the risk of complications.
Successful treatment of Q fever endocarditis is much more difficult. Tetracycline or doxycycline given in combination with trimethoprim-sulfamethoxazole (TMP-SMX) or rifampin for 12 months or longer has been successful in some cases. However, valve replacement is often required to achieve a cure.
Preventative Measures
A vaccine is available for immunization of at-risk personnel is licensed in Australia. Vaccination with a single dose provides complete protection against naturally occurring Q fever, and greater than 95% protection against aerosol exposure. Protection lasts for at least 5 years.
The use of this vaccine in immune individuals may cause severe local hardening around the site of injection, sterile abscess formation, and even necrosis at the inoculation site.
Antibiotics
ChemoPrevention using Tetracycline 500 mg every 6 hours or doxycycline 100 mg every 12 hours for 5-7 days is effective if begun 8-12 days post exposure.
WARNING! Drug therapy is not effective and may only prolong the onset of disease if given immediately (1 to 7 days) after exposure.