Q fever: more common than we think, and what this means for prevention

Raising awareness of the disease and ensuring access to vaccination for all at risk should be priorities

Australia has one of the highest Q fever notification rates in the world. The article on seroprevalence data in this issue of the MJA1 reinforces the fact that Q fever is an infection of public health significance, and suggests that infections are more common than is recognised.

Acute Q fever is protean in its manifestations, ranging from non‐specific febrile illness to hepatitis and pneumonia. Hospital admission is often necessary, although asymptomatic infections are also common. Early treatment may reduce the risk of persistent focal infections (most frequent: endocarditis) that affect about 4% of those infected.2 Persistent fatigue burdens as many as 60% of patients 12 months after infection; the exact pathogenesis of this symptom is unknown, but the impact on quality of life can be debilitating.3

The previously described discrepancy between the rates of Q fever seroprevalence and symptomatic illness is explained by a combination of asymptomatic and self‐resolving infections, non‐specific clinical presentations, lack of awareness of the manifestations of the disease, and the low sensitivity of serological diagnosis early in the course of acute Q fever. Gidding and colleagues suggest that underdiagnosis is a major problem; only 11% of seropositive unvaccinated people in their cohort had been diagnosed with Q fever. Adding polymerase chain reaction detection of Coxiella burnetii to diagnostic test algorithms has in the meantime improved case detection in the Netherlands4 and in some Australian laboratories.5 Appropriate laboratory testing is crucial for diagnosing Q fever and should be considered whenever a patient who has resided in a rural area and is classified as being at risk presents with an otherwise unexplained febrile illness.

The authors observe that their seroprevalence data indicate that Q fever in women, in particular, is more common than the notification data suggest. The prevalence of Q fever in children (not evaluated in this study) may also be underestimated. Notifications of Q fever in children are rare, but serological studies have found evidence of exposure in as many as 2.5% of children in Queensland, and severe complications, such as chronic recurrent multifocal osteomyelitis, have been described.6

Preventive strategies

Improving our understanding of non‐traditional risk factors is important for developing prevention strategies. Recent descriptions of small outbreaks in veterinary clinics and catteries in Australia have highlighted the fact that companion animals are potentially unrecognised sources of Q fever.7 The Australian Immunisation Handbook therefore now recommends vaccination for people working in veterinary clinics or animal refuges (Box).8 The possible association of seropositivity with exposure to pigs in the study by Gidding and colleagues is interesting. Meat workers who work exclusively with pigs are not considered to be at particular risk and were not included in the 2001–2005 National Q Fever Management Program. In addition to direct animal exposure, environmental contamination may also result in community exposure to the spores of C. burnetii.

Their findings led Gidding and her co‐authors to recommend expanding the indications for Q fever vaccination. Recommending it for all Australian rural residents may be premature in the absence of data from other regions, but it should be considered for all those living in country Queensland and New South Wales, as both direct and indirect animal exposure may pose significant risks for infection in these settings of high prevalence.

Understanding the barriers to implementing Q fever vaccination programs is important if such an expansion is to succeed. Knowledge about Q fever and awareness of vaccine availability and its indications are critical. The potential for adverse local reactions to the vaccine also affects implementation, especially as pre‐vaccination screening (humoral antibody and cell‐mediated skin testing) is required. The need for at least two visits to a general practitioner, access to intradermal skin testing, and cost are all potential barriers, and new strategies — such as a single blood assay of γ‐interferon production on exposure to C. burnetii antigen (Q‐detect, Innatoss) — may facilitate a simpler pre‐vaccination screening protocol.9 Data regarding Q fever vaccination of children at risk are scant, and its safety and efficacy in this important risk group require further investigation.

Australia has a proud history in the discovery and investigation of Q fever, including the first description of the illness, the characterisation of its aetiology, and the development of the only vaccine in clinical use.10 Many questions remain, and future research should focus on prevention strategies that raise awareness and ensure access to safe and easily deliverable vaccine for all those at risk, including children.