Q fever or ‘query fever’ is a vaccine-preventable zoonosis first described in Australia in 1937⁷. The causative agent⁸ for this disease is the obligate intracellular coccobacillus Coxiella burnetii. The bacterium has two structural versions called large cell and small cell variants (LCV and SCV) – and two antigenic forms, Phase I and Phase II. The SCV exhibits exceptional environmental resistance, surviving on wool, meat, and milk for periods ranging from one to 40 months after being shed from infected animals. Diagnosis has traditionally been made by detecting antibodies against the Phase II forms. But antibodies wane over time, and more sensitive and faster DNA-based PCR testing may be identifying a greater number of cases of this underdiagnosed disease.

How do humans get infected?

Zoonotic infections from infected animals can enter humans via inhalation, skin abrasions, splashes of pathogen-containing material into the eye, or the consumption of raw and unpasteurized materials from infected animals.

Cattle, sheep and goats are considered reservoir hosts.¹¹ In rural areas, kangaroos can also be carriers, and a range of other animals can be infected, including camels, llamas, alpacas, rodents, cats, dogs, birds, wallabies and other marsupials.¹¹

Inhalation of the organisms due to exposure to contaminated aerosols and dust containing dried infected animal discharges is considered a common mechanism of human infection.

You might see how droughts (plus wind) and floods could help stir up and distribute such hardy bacteria via dust and mud. By extension, the spread of this pathogen will be exacerbated by climate change.

Most infections occur among rural and remote communities. However, there are signs that urban populations may have similar antibody prevalence, suggesting that exposures may affect a greater number of people than was previously understood despite the urban group not traditionally manifesting as many symptomatic cases.¹⁴ More and better testing may now be a driver for the identification of more acute urban cases.¹⁷

What can Q fever do to the infected human?

Q Fever can have an incubation period of up to six weeks. Infections can be asymptomatic in 60% of cases or can manifest as an acute flu-like illness characterised by symptoms such as chills, fever, profuse sweating, cough, severe headache, nausea, vomiting, diarrhoea, muscle pains, and weakness.

C. burnetii circulates through the body via the bloodstream, so any organ system can be exposed.

Acute C. burnetii can be treated with a course of antibiotics (doxycycline). The sooner treatment starts – which can be aided by rapid diagnosis – the better the speed of recovery.¹⁸ Chronic cases are more complex to manage.¹⁷

Severe disease includes pneumonia⁴, hepatitis and meningitis. Acute Q fever can progress to chronic Q fever², with manifestations including endocarditis, aortitis, and osteoarticular manifestations¹. Q fever in pregnancy³ increases the risk of abortions early on and prematurity or intrauterine fetal death in later pregnancy.

Q fever in Australia

While Q Fever is not caused by a virus, I recently had some experience working on molecular test development in a pathology setting, and so this particular pathogen and I have a history I’d like to keep alive. In that context, here’s a snapshot of Australia’s interesting Q Fever numbers.

One thing you’ll notice right away is that the Australian states of New South Wales¹² and Queensland^13,16 have the highest number of detections.

Both States have well-equipped C. burnetii serological and molecular testing laboratories (including PCR-based methods and access to genomic sequencing) that can process and detect C. burnetii in samples quickly and reliably in a high quality-controlled environment. I can’t speak to how testing awareness and test ordering habits among doctors may have changed over time or how they differ from other jurisdictions.

Notably, molecular testing enables faster diagnosis and subsequent treatment than antibody testing because the latter requires two weeks⁹ between samples to allow a person to produce a suitably detectable rise in antibody levels, which reflect acute infection. Faster results are better for patients.

Australian detection throughout history.

I’ve thrown together all the years for which the National Notifiable Disease Surveillance System (NNDSS)⁵ has public data. It’s a messy graph, I know.

However, you can possibly see that between 1991 and 2023 (with 1993, 2002, and 2003 being exceptions), the monthly total detections usually ranged within 30 and 60 cases.

The most recent year, 2025, for this post, is shown in red as a dashed line. Obviously, June is just starting, so its numbers are low.

2021-2024 uses diamond-shaped markers for each month to distinguish those tallies from the circles used to mark the months for all other years. To help you pick them out, especially if discriminating between colours is not easy.

Age and sex tell a story

This is a disease primarily affecting adults, rather than infants and young children. Q Fever’s symptomatic impact is also more frequently identified among men than women. Male sex is a risk factor for symptomatic disease.

The same pattern is also apparent in the 2025 data (not shown here).

It’s likely the over-representation of males reflects occupational exposure among male-dominated roles that come into contact with infected animals including^10,11:

• Abattoir and meat workers
• Agriculture, livestock and dairy farmers and workers
• Stockyard/feedlot workers and transporters of animals, animal products and waste
• Shearers, wool classers/sorters, pelt and hide processors
• Knackery workers
• Tannery workers
• Laundry workers handling clothing from at-risk workplaces
• Pet food manufacturing workers
• Veterinarians, veterinary nurses/students/researchers, and others working with veterinary specimens
• Agriculture college staff and students working with high-risk animals
• Animal shooters/hunters
• Laboratory personnel working with materials containing the bacterium C. burnetii
• Wildlife/zoo workers, animal trainers
• Dog/cat breeders, and anyone regularly exposed to pregnant or birthing animals.

Apart from direct contact with animals, there is the risk of infection from contaminated environmental exposures. This includes:

• Family members of the high-risk occupational groups described above, through exposures to contaminated clothes, boots or equipment
• People living on or in close proximity to a high-risk industry (e.g. neighbouring livestock farms, stockyards housing cattle/sheep/goats, meatworks, land being fertilised by untreated animal manure)
• Visitors to contaminated environments (e.g. farms, abattoirs, animal sale yards)
• People living near livestock transport routes who may be exposed to contaminated dust from passing animals
• People involved in mowing, which stirs up dust contaminated by animal excreta, in areas where there are livestock or native animals, commonly kangaroos
• People who observe or assist animal births. Agriculture/farming

As is often the case with infectious diseases – but not specifically shown in these data – immunocompromised people are also at greater risk of more severe outcomes.

Clarifying the mess

To make it neater, I’ve reduced the years shown above.

This new graph highlights that 2024 was a big year. In fact, it produced the largest annual total of Q Fever notifications on record in Australia, with 874 cases detected.

Here’s an even simpler view: the annual totals graph.

There was some local media noise about 2024.

Unfortunately, it didn’t include analysis of potential changes in laboratory practices and assumed that more detections were, by default, due to a surge of new infections. But that’s not a done deal without more research. There are hints that the lab may be driving these increased numbers, though.

The Q Fever literature predicts this disease has long been considered an underdiagnosed infection. Experts from Queensland^9,10 have also suggested this.

Increased surveillance and improved laboratory testing methods and processes are possible contributing factors to the apparent increase in new infections. In other words, it may be that laboratory improvements in recent years are better at identifying what has been causing illness among us all along.

More broadly targeted communication, aimed beyond already well-educated abattoir workers, could update other groups at high risk of C. burnetii exposure. Increased awareness may help reduce infections. Also, more widespread use of the effective Q Fever vaccine should reduce the risk of symptomatic Q Fever requiring a hospital visit among those who have regular animal contact.¹⁵

I’ll be keeping an eye on Q Fever numbers in the future, both here and more frequently on Bluesky, if you’d like to follow along.

References

1. Osteoarticular manifestations of Q fever: a case series and literature review
   https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(18)30211-8/fulltext
2. CHRONIC Q FEVER AS RECURRENT OSTEOARTICULAR INFECTION IN CHILDREN: CASE REPORT AND LITERATURE REVIEW
   https://pubmed.ncbi.nlm.nih.gov/36223236/
3. Q fever during pregnancy: a narrative review
   https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(19)30560-9/fulltext
4. Q Fever pneumonia
   https://pubmed.ncbi.nlm.nih.gov/20171543/
5. National Notifiable Disease Surveillance System (NNDSS)
   https://nindss.health.gov.au/pbi-dashboard/
6. Q fever case spike in Qld drives renewed push for more accessible vaccine for ‘nasty’ bacterial disease
   https://www.abc.net.au/news/rural/2024-03-14/q-fever-cases-spike-queensland-/103576250
7. “Q” FEVER, A NEW FEVER ENTITY: CLINICAL FEATURES, DIAGNOSIS AND LABORATORY INVESTIGATION
   https://onlinelibrary.wiley.com/doi/abs/10.5694/j.1326-5377.1937.tb43743.x
8. Q Fever
   https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(06)68266-4/fulltext
9. Australians at risk as data reveals severe underdiagnosis of Q Fever
   https://www.rcpa.edu.au/Library/Publications/PathWay/Docs/Australians-at-risk-as-data-reveals-severe-underdi
10. The improving state of Q fever surveillance. A review of Queensland notifications, 2003-2017
    https://pubmed.ncbi.nlm.nih.gov/32536338/
11. Q fever, Queensland Government
    https://www.qld.gov.au/health/condition/infections-and-parasites/bacterial-infections/q-fever#
12. NSW Health Pathology Test Catalogue (Q Fever)
    https://catalogue.pathology.health.nsw.gov.au/search?searchValue=q%20fever&searchType=startsWith&page=2&pageSize=10
13. Pathology Queensland Test List (search for Q fever)
    https://www.health.qld.gov.au/public-health/pathology-queensland/healthcare/testing/test-list
14. Q fever seroprevalence in metropolitan samples is similar to rural/remote samples in Queensland, Australia
    https://link.springer.com/article/10.1007/s10096-011-1225-y
15. Q fever vaccine efficacy and occupational exposure risk in Queensland, Australia: A retrospective cohort study.
    https://www.sciencedirect.com/science/article/pii/S0264410X20310276#
16. Q Fever Interest Group (QFIG) webpage
    https://medical-school.uq.edu.au/research/research-groups/infective-endocarditis-queensland-ieq/q-fever/qfig/q2030
17. Evolving epidemiology of Q fever in Wide Bay
    http://www.hpv.health.gov.au/internet/main/publishing.nsf/Content/458DD8840E8C9332CA25891F0015C89D/$File/evolving_epidemiology_of_q_fever_in_wide_bay.pdf
18. Q fever cases are rising
    https://www.dairynewsaustralia.com.au/news/q-fever-cases-are-rising/