Q Fever Endocarditis May be Underreported in the United States

Q Fever is an often-asymptomatic infection caused by the bacteria Coxiella burnetii, which naturally infects animals such as goats, sheep, and cattle. The bacteria can be “found in the birth products, urine, feces, and milk of infected animals,” according to the Centers for Disease Control and Prevention (CDC), and individuals can become infected after breathing in contaminated dust.

Despite being designated a nationally notifiable disease in 1999, Q Fever is likely underreported and a heavier burden on the United States population than it is presently considered to be, said Anne Straily, DVM, MPH, in an oral presentation at the 2017 Annual CDC Epidemic Intelligence Service (EIS) Convention in Atlanta, Georgia, on April 24, 2017.

“There are many associated conditions with Q fever, including endocarditis,” noted Dr. Straily, adding that although more than half (about 60%) of Q fever infections do not result in physical symptoms directly resulting from the fever itself, potential associated conditions, such as endocarditis, and the exacerbation of existing conditions can still be deadly. Endocarditis, a bacterial infection in the inner lining of the heart, generally occurs when bacteria enter the bloodstream and spread to already-damaged areas of the heart. If endocarditis is left untreated, it can erode heart valves and even be fatal. The condition may be treated with antibiotics or, in some cases, surgery. Those individuals with existing damage to their hearts or with compromised cardiac function are the most susceptible to endocarditis.

Perhaps equally as alarming, because of Q fever’s potential association with bioterrorism, state and local health departments have been instructed to report cases of infection to the CDC via the National Notifiable Disease Surveillance System and by using case report forms (CRFs).

“Few clinical details are collected about [cases where] the patient has Q fever and endocarditis, [though]” said Dr. Straily, adding, “Prospective analyses are needed to better understand these two conditions.”

For their research, Dr. Straily and her team conducted an evaluation of the largest case series of Q fever endocarditis in the United States when they pulled all CRFs submitted to the CDC between 1999 and 2015 to identify Q fever patients who also had endocarditis. The team evaluated 991 CRFs and pulled 93 cases of probable or confirmed Q fever and endocarditis. (In the original abstract, the team reported 57 cases were pulled.) They evaluated the cases to identify where the patients might have contracted Q fever and if any preexisting heart conditions were present.

“Patients who are most likely to get Q fever endocarditis are those who have preexisting damage to a heart valve or an artificial valve, but being immunocompromised is not necessary a preexisting condition,” said Dr. Straily. Interestingly, in the 7 cases that had preexisting valvulopathy specified on the CRF, 6 were associated with the aortic valve. When asked why that might be, Dr. Straily said that at this time, her team “does not have the answer.”

When the team evaluated the study population, several trends emerged. “The majority of cases were male, white, and hospitalized,” said Dr. Straily, adding that the Northeastern United States “contributed the fewest cases” to the case series. A total of 63% of the study population were over the age of 50, and most reported fever, malaise, and myalgia as their symptoms.

She noted that the study was limited because the data they reviewed was collected as part of a passive surveillance system and voluntarily submitted. Furthermore, “The national reporting system was developed specifically to identify acute Q fever, not chronic,” she said, indicating that this likely means that the chronic condition often associated with endocarditis is underreported and that “the low case fatality rate should be interpreted with caution.”

Dr. Straily and her team recommended additional prospective analyses to better understand how Q fever interacts with associated conditions like endocarditis and also how patients contract the illness. “We looked specifically at patients who were retired, but did not determine previous occupation or if they were necessarily employed at time of illness onset. Currently, this data is likely not being captured,” she said. She also noted that although animal exposure may be linked to contracting Q fever and that the researchers suspected that employment related to livestock exposure could also be linked to higher incidences of Q fever, more research would be necessary to determine a correlation.