Q fever is a disease caused by the bacterium Coxiella burnetii, which can be transmitted to humans from animals such as sheep, goats, and cattle. C. burnetii is considered a possible bioterrorism agent because it is quite hardy in the environment, infects people who breathe aerosols containing the organism, and has a very low infectious dose (one organism can cause disease in a susceptible person).
Recently, we at CDC’s Rickettsial Zoonoses Branch and our colleagues at the National Center for Health Statistics tested blood samples from the 2003-04 National Health and Nutrition Examination Survey (NHANES) and found that 3.1% of the general U.S. population have antibodies to C. burnetii. This means that as many as 9 million people in the U.S. have been exposed to Q fever at some point in their lives!
Additionally, in collaboration with the Rollins School of Public Health at Emory University, we tested 508 veterinarians and found that slightly more than 22% had antibodies to C. burnetii. This suggests that a large proportion of veterinarians become infected with these bacteria, probably through exposure to infected livestock. An increasing number of Q fever cases have also been reported in military personnel serving in Iraq and Afghanistan. Lastly, we at RZB conducted a study to detect C. burnetii DNA in environmental samples collected across the U.S. (6 states including west coast, southwest, upper Midwest, east coast, southeast) and found 23.8% of all samples positive!
So why are these findings so surprising? Fewer than 200 cases of Q fever are reported each year in the United States, meaning that most cases of Q fever are going unnoticed.
The good news: Most people infected with C. burnetii show no signs of disease or develop a mild illness, and the vast majority of infected people recover from Q fever, even without treatment.
The bad news: About 1% of infections may become chronic and lead to life-threatening inflammation of the heart. Chronic infection is more likely in people who have pre-existing heart problems or weak immune systems. Pregnant women are also at high risk of infection that can lead to complications for the mother and fetus.
Now that we know Q fever is seriously underreported, we are working on new ways to prevent transmission to humans and diagnose cases early. By identifying cases early, we can prevent some of the complications caused by this disease.