Q fever

From Ganfyd

Introduction

An atypical pneumonia caused by the rickettsia Coxiella burnetti. In contrast to other rickettsial infections, Q fever is spread by inhalation of aerosols containing the infective organism, with a infectious dose of as few as 10 bacteria. Transmission through direct contact of human mucosal membranes with infectious animal bodily fluids is also recognised, as is consumption of raw milk from infected animals.^[1]

The organism can infect animal populations, with spread within animals by tick vectors, hence outbreaks in abbattoirs. The spore form of the organism can persist in the environment for long periods despite harsh conditions.

Consider in culture negative endocarditis, so-called atypical pneumonias and PUOs.

There has been a large outbreak of Q fever in the Netherlands, which has been ongoing since 2007.^[2] Given the protean presentation of the disease, it is possible that there are also many undiagnosed cases in the UK, particularly in sheep farming areas.

Aetiology

A zoonosis caused by the rickettsia Coxiella burnetti.

Clinical

Investigations

Diagnosis mainly through serology, but the interpretation of results is far from straight-forward.^[3] Complement binding reaction tests are the most reliable; ELISA and immunofluorescence assay (IFA) testing may also be used. IFA testing is particularly difficult to interpret, because of the differing roles of IgG phase one and phase two.

PCR tests may be positive in the first two weeks after onset of infection. As with other tests (e.g. for measles) the PCR test will be positive earlier, as it detects bacterial DNA, and serological tests will become positive later. As there may be flare-ups or exacerbations, PCR may be intermittently positive.

Blood tests

Radiology

Treatment

Medical

Treatment is with antibiotics - usually doxycycline in combination with another antibiotic such as a quinolone, trimethoprim or rifampicin.

Surgical

Not applicable.

Prevention

According to CDC, the following measures should be used in the prevention and control of Q fever:^[4]

• Educate the public on sources of infection.
• Appropriately dispose of placenta, birth products, fetal membranes, and aborted fetuses at facilities housing sheep and goats.
• Restrict access to barns and laboratories used in housing potentially infected animals.
• Use only pasteurized milk and milk products.
• Use appropriate procedures for bagging, autoclaving, and washing of laboratory clothing.
• Vaccinate (where possible) individuals engaged in research with pregnant sheep or live C. burnetii.
• Quarantine imported animals.
• Ensure that holding facilities for sheep should be located away from populated areas. Animals should be routinely tested for antibodies to C. burnetii, and measures should be implemented to prevent airflow to other occupied areas.
• Counsel persons at highest risk for developing chronic Q fever, especially persons with pre-existing cardiac valvular disease or individuals with vascular grafts.

The contrast between recommending vaccination of those who are "engaged in research with pregnant sheep" and not vaccinating those who work with them is curious. In Australia, where Q fever is more prevalent, vaccination is recommended for high risk workers. UK recommendations do not include vaccination.^[5]

Post exposure prophylaxis

Notification

ICD code

ICD-10_-_A00-B99

External links

• CDC page on Q fever
• Wikipedia page on Q fever
• NHS choices introductory page on Q fever
• Medline Plus page on Q fever
• Netherlands Ministry of Agriculture Q fever pages (in English)

Other recommended reading

Prof Barry Marmion of Australia has published extensively on Q fever. His booklet on Q fever is an excellent of the condition,^[6] but unfortunately it does not appear to be in the public domain.

References