Dr. Jeff Hersh: Q fever explained

Dr. Jeff Hersh

Q: One of the soldiers my son-in-law knew from his service in Iraq developed pneumonia that they thought may be due to Q fever. Would you tell me about this disease?

A: Q fever is named for query fever, which is what it was called before the 1937 discovery that it is caused by the Rickettsia bacteria Coxiella burnetii.

It is a worldwide zoonosis, meaning it also infects animals, which, in this case, includes livestock, birds and small mammals. It typically infects humans when they inhale aerosolized bacteria from dust contaminated from the fluids an infected animal (there has been only one documented case of human-to-human transmission, and infection from a tick bite is thought to be rare).

Coxiella burnetii is very virulent; even one bacterium can cause disease. It is difficult to inactivate and it can survive for months in dust.

Q fever is uncommon. There are fewer than 200 human cases per year reported in the U.S. (fewer than one per million Americans per year). However, it is a worldwide disease, and occasionally there are outbreaks in certain places. For example, there have been almost 4,000 cases of Q fever in the Netherlands since 2007, although so far none have been reported in Americans who have traveled there. Since 2003, there have been more than 200 cases reported in military personnel returning from Iraq.

The Centers for Disease Control and Prevention recently issued a health advisory for Q fever for returning military personnel from Iraq, and have also increased awareness of the outbreak in the Netherlands.

About half the people infected with Coxiella burnetii have no symptoms and the condition resolves with no treatment. For people who do get sick, typically after an incubation period of one to six weeks, the most common symptoms are non-specific and "flu-like" such as fever, body aches, weakness and/or nausea/vomiting. Respiratory symptoms including cough, chest pain and/or shortness of breath often develop a few days later. Some people develop pneumonia, and some develop an inflammation of the liver (hepatitis).

Antibiotics can shorten the duration of these illnesses, although even without treatment most of these patients have the disease resolve on its own.

However, about 1 percent to 5 percent of infected people develop a more severe chronic condition, likely because the bacteria reproduce inside macrophages (a type of white blood cell that helps fight foreign material introduced to the body). The bacteria can also bind to a patient's heart valve (more common if there are abnormalities of a heart valve from previous disease, such a rheumatic fever), a condition called endocarditis. Patients with these chronic infections may require prolonged antibiotic treatment, lasting a year or even longer.

Q fever is diagnosed by specialized blood tests that look for antibodies to Coxiella burnetii. Other tests are possible, including culturing of the bacteria, but this must be done under strict bio-safety protocols. Other tests depend on the patient's symptoms, and may include a chest X-ray (to evaluate for pneumonia), liver tests (to evaluate for hepatitis) and an echocardiogram or other tests (to evaluate for endocarditis).

The discussion above shows why Coxiella burnetii is classified as a Category B bioterrorism agent by the CDC; it is moderately easy to disseminate, causes moderate morbidity and/or mortality and requires enhanced testing and surveillance capacity.

A vaccine to prevent Q fever has been developed and is used in Australia for high-risk people, and it has been shown to be effective. However, this vaccine is not available in the U.S.

Overall, about 1 percent of people infected with Coxiella burnetii die from it. Because of this and its bioterrorism potential, vigilance and suspicion of this disease is important to help identify outbreaks.

Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at