What is Q fever?

Q fever is a highly infectious zoonosis (human infection of animal origin) caused by the organism Coxiella burnetii. This bacterium is widespread globally among livestock and domestic ruminants (sheep, cattle and goats) are the most frequent source of human infection, though dogs, cats and arthropods may also be a source. The peak incidence of infection in humans in the UK is associated with the spring or early summer lambing season.

What is its bioterrorism potential?

Coxiella burnetii could be used as a biological weapon in an aerosolised form or as a contaminant of food, water, mail or other items. An aerosol would be the most efficient form of release; a single organism can cause disease if inhaled by a susceptible individual, and there is good evidence as to the role of wind transmission. Its ability to form resistant spore-like forms, remain viable in the environment for years after release, and its stability under production, storage and transport conditions also make it a suitable biological weapon.

How do you catch Q fever?

Aerosols are the major route of transmission to man either from direct exposure to infected tissues or indirectly through contaminated dust. Humans are at greatest risk of exposure during livestock deliveries or abortions because primary aerosols containing large numbers of Coxiella burnetii are shed at that time. Wind-borne transmission of aerosols has caused outbreaks. C. burnetii may also be inoculated through cuts in the skin. Person-to-person spread is not generally recognised.

How long can you have the infection before developing symptoms?

In acute infections the incubation period is between 7 and 30 days, depending on the infecting dose, route of exposure and age of the patient. Patients developing chronic infections, such as endocarditis, may remain infected without showing symptoms; however relapses may occur months or years in the future.

What are the symptoms?

Around half the people infected with Q fever show symptoms of acute infection which is usually characterised by an influenza-like-illness; other common presentations include atypical pneumonia and hepatitis. Fever and fatigue are the most prominent manifestations and headache is common. Only about 5% of symptomatic patients require hospitalisation. Since Q fever presents as a non-specific febrile illness or an atypical pneumonia it may be difficult to distinguish it clinically from viral illnesses or other causes of atypical pneumonia.

Most people make an uneventful recovery from acute Q fever, however in some cases the infection becomes chronic leading to endocarditis, chronic hepatitis, chronic fatigue, osteomyelitis, septic arthritis, chronic intestitial lung disease or infection of aneurysms and vascular grafts. Onset of chronic disease usually occurs about 6 months following acute infection (with a range from 1 month to several years).

How is Q fever treated?

The treatment of choice for acute Q fever is doxycycline or tetracycline for 7-14 days with treatment continued for at least three days after remission of fever.

Antibiotics are less effective in chronic disease and despite improved results with combination therapy(doxycycline and chloroquine) relapse rates of over 50% are still seen and a minimum of 3 years treatment is recommended.

Can Q fever be prevented?

As Q fever is mainly an occupational disease prevention and control measures are usually directed at these occupational groups and environments. For example, restriction of access to potentially infected animals and appropriate disposal of animal birth products. In the event of a release of Q fever, individuals in the exposed zone can be treated with antibiotics given a week after exposure. There is no vaccine available in the UK.

How common is Q fever?

Coxiella burnetii has a worldwide distribution. In humans Q fever is strongly associated with certain occupations e.g. farmers, abattoir and meat packing workers. Q fever causes less than 5% of community acquired pneumonia in the UK and about 70 cases are reported each year. This probably underestimates the true incidence of Q fever because many of cases are mild or show no symptoms.