Q fever

Notification requirement for Q fever

Q fever infection is a ‘routine’ notifiable condition and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centre exclusion for Q fever

Exclusion is not applicable.

Infectious agent of Q fever

The rickettsia-like Gram-negative coccobacillus bacterium Coxiella burnetii is the causative agent.

Identification of Q fever

Clinical features

The onset of Q fever infection is usually acute and characterised by fever, chills, sweats, severe headache (especially behind the eyes), weakness, anorexia, myalgia and cough. Pneumonia is another acute presentation and can range from mild to severe. Abnormal liver function tests (hepatitis) are common, while transient mild rashes are an occasional feature. Orchitis occurs rarely. Nonetheless, almost 60 per cent of cases are asymptomatic.

Chronic complications include granulomatous hepatitis, chronic fatigue syndrome, osteomyelitis and endocarditis. The latter is the most serious concern, as it usually involves the aortic valve and occurs months to years after the acute illness, especially in those with underlying valvular heart disease.

Diagnosis

Acute and some chronic manifestations of Q fever can be diagnosed by serology.

Acute Q fever can be diagnosed by a fourfold rise in specific complement fixation (CF) antibodies or direct immunofluorescence antibody testing between acute-phase and convalescent-phase sera collected at least 14 days apart.

The diagnosis is supported by the detection of phase II IgM by ELISA testing, but this may not appear until 10 days after the onset of symptoms. Q fever IgM may persist for many months after infection; hence, its presence does not necessarily confirm the diagnosis.

If Q fever antibodies are present within 3–4 days of the onset of symptoms, this is more likely to indicate past exposure than recent infection.

Chronic Q fever is suggested by a high CF antibody titre (≥320) to phase I and II antigens and low or absent IgM antibody.

IgA class antibody to phase I antigen is highly suggestive of Q fever endocarditis.

Cross-reactive serologies have been extensively reported for pathogens such as Legionella spp., Mycoplasma pneumoniae, Rickettsia spp., Chlamydia spp., parvovirus, Bordetella pertussis, Epstein–Barr virus and cytomegalovirus. Almost 50 per cent of cases have cross-reactive serology for Bartonella spp.

Polymerase chain reaction (PCR) can also be used for diagnosis on blood (most sensitive during acute illness) or tissue (for example, valvular tissue for endocarditis), especially in the setting of cross-reactive serology.

Incubation period of Coxiella burnetii

The incubation period is typically 14–21 days, although the range is from 3 to 30 days.

Public health significance and occurrence of Q fever

Q fever is an acute febrile rickettsial disease of low mortality but significant morbidity. It is most commonly found in abattoir workers who have recently handled contaminated stock, such as feral goats or sheep from endemic areas. It is an occupational hazard for tannery and knackery workers, shearers, meat inspectors, dairy workers, animal-farm workers, animal transporters, wool sorters and veterinary personnel. It also occurs in others handling fomites, such as those laundering contaminated clothing.

Outbreaks are usually of short duration.

Reservoir of Coxiella burnetii

The organism is commonly found in stock, including goats, cattle, sheep, other farm and domestic animals, and in some wild animals (including kangaroos and bandicoots). Infected animals shed C. burnetii in milk, urine, faeces and birth products. It can survive for long periods in the environment (almost 9 months in wool, more than 1 month on fresh meat and 40 months in skim milk).

Mode of transmission of Coxiella burnetii

Q fever is contracted through the respiratory route after inhalation of Coxiella-contaminated dust or aerosols. This most commonly occurs as a result of:

• inhaling water droplets and dust contaminated by placental tissues, birth fluids or excreta of infected animals (contaminated dust particles may occasionally be carried downwind for a considerable distance from the source)
• direct contact with contaminated materials in establishments processing infected animals or their by-products, contact with contaminated straw, wool or hides, or contact with the contaminated clothing of workers.

Although Q fever is occasionally transmitted sexually, there is no evidence of person-to-person transmission through other routes. Direct transmission through blood and bone marrow transfusion has been reported.

Drinking unpasteurised milk from an infected animal has been suggested as a possible route, but this has not been proven.

Period of communicability of Q fever

Person-to-person spread rarely occurs. Immunity following recovery from clinical illness may be life-long. Antibodies are detectable for three to five years, but may persist as long as 15 years.

Susceptibility and resistance to Q fever

All nonimmune people are susceptible to infection. Most cases are in male adults, but this is probably due to their higher frequency of occupational exposure rather than differential susceptibility.

Infection usually confers lifelong immunity.

Control measures for Q fever

Preventive measures

Immunisation of those in high-risk occupational groups is the primary preventive measure against Q fever. There is a risk of severe local reactions to the vaccine in those people previously exposed to Q fever or the vaccine. To assess prior exposure, prevaccination screening is necessary. It involves:

• checking for a clinical history of Q fever or Q fever vaccination
• antibody testing
• an intradermal skin test, read after 7 days.

Any positive result on screening precludes vaccination.

Vaccination induces presumed lifelong immunity in most vaccinees. Vaccination efficacy in meta-analysis data has been reported at 100 per cent if given appropriately. Training is recommended for medical practitioners intending to conduct Q fever screening and vaccination.

Access to high-risk environments, such as abattoirs and meat-processing plants, should be restricted to immunised people. This includes visitors, contractors and delivery drivers. Workers in these environments should also be educated about the nature of the disease.

Control of case

Acute cases of Q fever generally require treatment with doxycycline. Consult the current version of Therapeutic guidelines: antibiotic.

In chronic disease or endocarditis, prolonged combination therapy together with cardiac surgery may be required. Generally, treatment consists of doxycycline 100 mg twice daily and hydroxychloroquine 200 mg three times a day for an extended duration (more than 12 months). Consultation with an infectious diseases physician should be sought.

Isolation is not necessary. Articles contaminated with blood, sputum and excreta should be disinfected using standard precautions.

Control of contacts

No specific measures are required for household contacts, although it is recommended that they do not handle potentially contaminated laundry from the case.

Vaccination during the incubation period does not prevent the disease. Post-exposure prophylaxis has also not demonstrated efficacy.

Control of environment

If a clear source is identified, disinfection can be performed using 0.05 per cent hypochlorite (500 ppm available chlorine) or 5 per cent peroxide.

Outbreak measures for Q fever

All notified cases are investigated to ascertain the most likely source of exposure and to identify any other linked cases. If two or more cases are linked in time and place to a workplace, other staff should be assessed for immune status (if not already known) with antibody levels and skin testing.

Nonimmune staff should be excluded from the worksite until vaccinated.