Q Fever: Background Information

Background

Q (standing for "Query") fever, was so called originally because for many years its cause was unknown. It is now known to be an infection with the organism Coxiella burnetii. It is usually, but not always, caught by direct contact with farm animals, especially sheep, cattle and goats. Most cases are sporadic; outbreaks are unpredictable but do occur and are more likely to affect urban (i.e. non-immune) populations.
Amongst animals, sheep, cattle and goats are most commonly infected although Q fever can also occur in domestic mammals and birds. Exposure to parturient cats is a recognised mode of transmission. A recent study in England and Wales suggested that up to 21% of dairy herds are infected. Infection in farm animals is usually asymptomatic, although there may be inflammation of the placenta, or an abortion. It is however uncommon as a diagnosis of abortion in sheep and cattle.

Epidemiology of human infection

Q fever is found worldwide. It is rare in the UK, causing less than 5% of cases of community-acquired pneumonia. Since 2000 the numbers of reported cases have declined annually and now there are usually less than 50 sporadic cases each year. However, outbreaks have occurred, sometimes in industrial settings; in Wales in 2002 (ref. 1) (which resulted in 95 cases), and in Scotland in 2006 (ref. 2). Q fever is strongly associated with certain occupations e.g. farmers, abattoir and meat packing workers, although often a defined exposure cannot be established. Q fever tends to be more common around the lambing season, although it can occur at any time of year. It is also more common in agricultural areas of the UK.

A very large outbreak has been ongoing in The Netherlands since 2007, with over 3000 humans cases diagnosed. The outbreak is linked to intensive goat farming in close proximity to residential areas. Link to HPR Report

The illness

Q fever is an acute (and sometimes chronic) febrile illness. The symptoms of acute infection are similar to influenza ('flu), and usually begin 2-3 weeks (range 2 to 40 days) after infection. Symptoms are variable, but the illness may be pneumonia-like, with some of the following:

• Severe headaches
• Fever (high temperature)
• Sore throat
• Sweats
• Muscle or joint pains
• Weight loss
• Sensitivity to light
• Dry cough
• Chest or abdominal pain

The onset of symptoms may be sudden, and they usually last for between 2 -14 days. However, some people who have Q fever won't have any symptoms at all, and only about 5% of symptomatic patients require hospitalisation. Some people who have had acute Q fever may develop a chronic form of the disease, where symptoms persist for more than six months. Rarely, endocarditis (infection of the valves of the heart) may occur. This generally occurs in people who already have damaged heart valves or who have had heart by-pass surgery. Tiredness and malaise can persist for some months after infection.

Q fever acquired during pregnancy is usually asymptomatic in the mother, however chronic infections may subsequently become apparent. Occasionally, acute Q fever in pregnancy, regardless of whether this is symptomatic or not, may result in an adverse effect on the foetus including prematurity, low birth weight, or abortion.

More details available here

Transmission

Transmission of Q fever occurs primarily through inhalation of contaminated aerosols. The organism is robust and can survive in dust and animal litter for many weeks, and in dried blood for at least 6 months at room temperature. The most infectious animal materials are the fluids of birth and afterbirth, followed by blood, milk, urine and faeces. Such infectious materials can be either livestock or domestic animal related, including parturient sheep, goats, cattle and cats.

The infectious dose can be as low as a single organism. Humans can acquire Q fever by:

• Inhalation of aerosols from placental tissue or amniotic fluids, or from urine, faeces or the carcass of infected animals
• Contaminated bedding or litter (hay or straw) from infected animals
• Inhaling airborne particles from the environment (dust, soil, straw and wool)
• Contact with infected material through cuts or abrasions in the skin, or through the conjunctiva
• Drinking infected unpasteurised milk

Transmission via a tick bite has also been reported, but this route of transmission has not been recorded in the UK. It can be spread from person to person, but this is very rare.

Risk factors

Q fever is generally associated with certain types of employment. A study of 400 farmers and country dwellers found serological evidence of past Q fever infection in 27%. The study found that occupational exposure was important in acquiring the infection, and that infection is related to the extent of animal exposure. Men are about 2.5 times more likely to be identified with Q fever than women, due mainly to occupational exposure. Infections in children are uncommon.

Pregnant women, immunosuppressed individuals and those with congenital or acquired heart valve disease or vascular grafts, should avoid jobs which may expose them to the risk of acquiring Q fever.

Diagnosis, treatment and prevention (see also Guidelines)

The diagnosis is confirmed by serological (blood) testing. In most people, Q fever requires no treatment and symptoms will resolve on their own. Treatment may be required if symptoms are severe or continue for several weeks, or if they return after the initial infection. 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.

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.

Pregnant women (and other at risk persons) should avoid close contact with sheep and lambs during the lambing season, so as not to risk their own health and that of their unborn child, from infections that can occur in some ewes. Other livestock and domestic animals may also pose a hazard for Q fever, and therefore exposure to cattle, goats or cats, which are in the process of giving birth or in the post-partum period, should also be avoided.

There is no vaccine against Q fever available in the UK.

References

1. Q Fever Outbreak in Industrial Setting. van Woerden et al. Emerging Infectious Diseases 2004, vol 10(7);1282-9. Accessed at: http://www.cdc.gov/ncidod/eid/vol10no7/03-0536.htm

2. Outbreak of Q fever in workers at a meat processing plant in Scotland, July 2006. Donaghy M, Prempeh H, Macdonald N. Eurosurveillance Weekly, 24 August 2006. Accessed at: http://www.eurosurveillance.org/ew/2006/060824.asp#2

Last reviewed: 6 August 2010