Anyone living in country Australia should consider being vaccinated against Q fever, according to researchers.
The recommendation was made on the basis of their study, published in the Medical Journal of Australia which showed that living in a rural area for more than three months was associated with an increased risk of contracting Q fever even if there was little contact with farm animals, the traditional reservoir of the infection.
In fact, the risk among country dwellers was 2.5 times higher than among people who had never lived rurally, according to the study which looked for evidence of past infection among 2740 blood donors in Queensland and NSW.
“The prevalence of Q fever, caused by Coxiella burnetii, is substantial in Australia despite the availability of a safe and effective vaccine,” the study authors wrote.
They point to stats that show that between 2013 and 2017 there were more 2500 notifications of Q fever in this country. They say this is very likely to be an underestimate, as most infections (up to 80%) are asymptomatic and sometimes they may have non-specific symptoms.
But what we do know is that when Q fever does cause significant symptoms the morbidity can be substantial – pneumonia, hepatitis, endocarditis, and osteomyelitis. In addition, 10-15% of symptomatic patients will develop a protracted post-Q fever fatigue syndrome.
To check just how many people have or have had the condition, researchers assessed blood donors from metropolitan Sydney and Brisbane, as well as blood donors in rural areas, namely the Hunter New England region of NSW and Toowoomba in Queensland. As well as collecting data on exposure, occupation and vaccination, the sera of the subjects was tested for both the C. burnetii antibody (as a measure of past exposure) and C. burnetii DNA (measuring current infection).
No patient in the study was found to be currently infected with Q fever.
Overall, 3.6% of the participants had evidence of past infection. And even though seroprevalence was higher in the rural areas compared to metropolitan areas, a significant proportion of those people from the city who tested positive for past Q fever had a history of living in the country at some time in the past.
As you would expect, people working with sheep, cattle or goats, abattoir workers and people who had assisted at an animal birth were at highest risk. Vaccination of these people is already recommended.
Non-farming people who just lived in rural areas were found to be at risk.
“Having lived in a rural area, but with no or rare contact with sheep, cattle or goats, was itself an independent predictor of antibody seropositivity after accounting for the effects of other exposures”, the study authors said.
Hence the recommendation we vaccinate everyone living in the country. But, as an accompanying editorial points out, expanding the current vaccination program is not without its challenges. Screening for humoral antibody and cell-mediated skin testing is required prior to vaccination so the need for at least two GP visits, access to intradermal skin testing and the cost are all potential barriers, the editorial authors said.
There is also an issue with a lack of evidence about the safety and effectiveness of the Q fever vaccine in children.
Nonetheless, all the experts agree: if we want to reduce the burden of Q fever in Australia, we will need to look beyond the select populations we are currently targeting for vaccination because there are obviously risk factors other than sheep, cattle and goats, at play.
Gidding HF, Faddy HM, Durrheim DN, Graves SR, Nguyen C, Hutchinson P, Massey P, Wood N. Seroprevalence of Q fever among metropolitan and non‐metropolitan blood donors in New South Wales and Queensland, 2014–2015. Med J Aust. 2019 Apr; 210(7): 309-15. DOI: 10.5694/mja2.13004
Francis JR, Robson JM. Q fever: more common than we think, and what this means for prevention. Med J Aust. 2019 Apr; 210(7): 305-6. DOI: 10.5694/mja2.50024