What Is Q Fever?
Q fever is a condition caused by a gram-negative bacterium known as Coxiella burnetii. It is an organism that affects both animals and humans. Although uncommon, it can be found in domestic mammals such as sheep, goats, cattle, cats, and dogs. It occurs worldwide (except New Zealand) but has been most commonly reported in Australia and France.
Coxiella burnetii is excreted in feces, milk, urine, and birth products. When these products are dried, it can become aerosolized. Since it is highly infectious, disease can be caused by a mere few organisms. Due to the life cycle of C. burnetii, the organism can stay virulent and viable for months.
1. History
This condition was first described by Edward Derrick in 1937 due to a cluster of acute febrile illness that occurred in Brisbane, Australia. It is called Q fever as the “Q” stands for “query,” which is due to the elusiveness of the disease etiology. Burnet and Freeman then isolated the causative organism and identified it as a Rickettsia species. Davis and Cox were then able to identify vector transmission in 1938 when this organism was found in ticks collected in Montana for the investigation of Rocky Mountain spotted fever. This organism was first known as Rickettsia diaporica, subsequently Rickettsia burnetii, and in 1948, was named Coxiella burnetii. It is a zoonotic disease which is no longer regarded as closely related to Rickettsiae but is a proteobacterium similar to Francisella and Legionella.
2. Etiology
Q fever is a common zoonotic disease caused by Coxiella burnetii. This organism is usually related to inhalation of organisms due to occupational exposure, animal exposure, and tick bites. This organism localizes in the uterus, mammary glands, and feces of small and domestic mammals. Due to the persistence of the organism’s spore like structure, it is highly resistant and can survive for months in feces and dust particles.
It can also infect individuals who have no contact with animals. For example, laboratory outbreaks and outbreak among people living along a road contaminated by farm vehicles that carry manure and straw. This organism can be transmitted via skin contact, inhalation, and rarely transmission by a tick bite. Other rare methods of transmission include blood transfusions, exposure to infected placenta, and sexual transmission. Infection in animals often goes unnoticed.
3. Epidemiology
In the United States in 1999, Q fever became a reportable disease (for the exception of some states: Iowa, Vermont, Delaware, Oklahoma, West Virginia). The annual incidence before 1999 was 21 cases. It then rose to 51 cases from 2000 to 2004. In 2005, 136 cases and in 2006, 169 cases were reported to the Centers for Disease Control and Prevention (CDC).
In 2006, it was reported to be 0.06 cases per 100,000 individuals. Since 2003, there have been more than 200 cases reported among US military personnel. Globally, it ranges about 5% in urban areas to 30% in rural areas. Since some cases of Q fever may have little to no symptoms, the incidence may be underrepresented. Q fever is highly prevalent in Spain, the Middle East, and Southern France. There is no racial predilection but is more common among females.
4. Signs and Symptoms
After exposure, the incubation period of Coxiella burnetii is generally 2 to 3 weeks. The commonest presentation seen in most patients are flu-like symptoms with malaise, fever, severe headache, profuse perspiration, joint pain, appetite loss, dry cough, confusion, chills, pleuritic pain (pain during breathing), upper respiratory issues, nausea, vomiting, gastrointestinal issues, and diarrhea.
It is important to note that about 50% of individuals with Q fever have no symptoms. During the course of the disease, the patient may develop atypical pneumonia, which can lead to acute respiratory distress syndrome. In some cases, there may also be pain in the upper right quadrant of the abdomen due to hepatitis or liver enlargement. Rarely, there may be jaundice and retinal vasculitis.
5. Diagnosis
The diagnosis of Q fever is highly dependent on the index of suspicion and proven by serologic analysis. Since the organism is highly infectious, isolation has to be done in biosafety level 3 laboratories. A clinician who suspects Q fever should notify the laboratory so proper precautions can be taken. An electrocardiography in Q fever patients may show abnormalities in the T-wave if pericarditis and myocarditis are present.
Other tests that may be beneficial are complete blood cell (CBC) count, liver function tests, and erythrocyte sedimentation rate. Confirmation of the diagnosis is based on serology (to look for an antibody response instead of the organism). Blood culture is difficult and not routinely performed. Transesophageal echocardiography may be useful as Q fever can cause endocarditis.
6. Treatment and Management
In Q fever, it is important to exclude other life-threatening diseases. While anti-microbial therapy is the first-line of treatment, most patients improve on their own. Once Q fever is diagnosed, antibiotic administration should be performed to prevent the disease from progressing to chronic disease, which can become resistant to treatment.
Additional measures include the use of antipyretics, antitussives, and supportive care with fluids to increase patient comfort. In some cases, surgery may be necessary, especially where there are cardiovascular complications such as valve replacement or mycotic aneurysm. Antibiotics should be continued after surgery as the organism may persist in the endocardial tissue after valve replacement. A consultation with an infectious diseases specialist is also required especially in patients with chronic Q fever.
7. Medications
Antibiotics treatment for Q fever helps to reduce the disease duration especially if it is started within 3 days after the onset of illness. Antibiotics are usually given for 14 to 21 days in the outpatient setting. The current treatment of choice is doxycycline with fluoroquinolones as an alternative. In cases where there is meningoencephalitis (inflammation of the meninges and brain), fluoroquinolones have an advantage as it has better cerebrospinal fluid (CSF) penetration.
Macrolides such as clarithromycin and azithromycin can also be used as alternatives. In chronic Q fever, a combination of doxycycline and hydroxychloroquine for at least 18 months is recommended. Alternative options include a combination of doxycycline and fluoroquinolone (3 to 4 years), or doxycycline or fluoroquinolones with rifampin.
8. Prognosis
Since acute Q fever is a self-limiting disease, proper diagnosis and treatment means that there is an excellent prognosis. Although 2% to 4% of patients require hospitalization, more than 50% of Q fever patients are asymptomatic. Among symptomatic patients, the mortality rate is less than 1%. In chronic Q fever, prolonged antimicrobial therapy with care from an infectious disease specialist will be required.
Despite adequate therapy, chronic Q fever has frequent relapses with mortality rates that can exceed 60%. The commonest cause of chronic Q fever is endocarditis. Without treatment, endocarditis is almost always fatal. With treatment, the overall mortality rate decreases to between 1% to 25%.
9. Complications and Patient Education
Some of the complications of Q fever are thrombocytopenia, acute respiratory distress syndrome, endocarditis (in chronic infection and can result in heart failure), reactivation of the disease during a pregnancy, spontaneous abortion, premature labor, increased rate of abortions, chronic fatigue syndrome, and meningoencephalitis.
In Q fever, patient education revolves around deterrence and avoidance of unpasteurized milk, dairy products, exposure to animal birth products, occupational exposure, tick bites, and more. Birth products such as aborted material, fetal membranes, and placentae should be disposed properly. Individuals who work with animals should maintain appropriate precautions when there is potential exposure.
10. Prevention
An Australian vaccine manufacturing company has developed a whole-cell inactivated vaccine for Q fever. It is an intradermal vaccination consisting of killed C. burnetii organisms. Tests should be performed to identify preexisting immunity as vaccination of individuals with an immunity can lead to a severe local reaction.
Vaccination results in many years of protective immunity. Australia also introduced a national Q fever vaccination program in 2001 for those who have occupations that put them at risk of the disease. Some have also recommended that vaccination of animals may help with control of the disease. There are several studies that reported vaccination on farms may help prevent issues in the animals such as abortion, metritis, silent estrus, and more.
