Coxiella burnetii (Q fever)

LEVELS: Highly unlikely; Moderate; Housing alone keeps it out; Reference or research laboratory required; NOT ASSIGNED; Negligible; NOT ASSIGNED; NOT ASSIGNED


Register id	`coxiella_burnetii`
Type	bacteria
Scientific name	Coxiella burnetii
NCBI taxid	777
Evidence	3 document(s)
Assigned	2026-09-04, against criteria version `093366e352a2`

Overview

Coxiella burnetii causes Q fever, a disease of people and ruminants in which the pig's role is essentially unknown. It is on this register because it appears on the published SHIC bacterial matrix and is a notifiable zoonosis, so its absence would have been conspicuous — not because there is a body of swine literature behind it. There is not: it has no chapter in Diseases of Swine, and everything held for it is serological. A southern Italian survey found 4.1% of sera from 32 commercial herds positive, with phase-specific testing suggesting both acute and chronic infections; US feral swine surveys found 0.19% seropositivity in Hawaii, 6.03% in Texas, and a companion study in California. None of these describes clinical disease in a pig, a route by which the organism enters a pig herd, or any US commercial data. In people the infection can be an acute self-limiting influenza-like illness or, less often, a chronic one, and it is acquired mainly by inhaling aerosols from infected ruminants. Because the swine evidence supports almost no claim about the disease in pigs, most of this entry's criteria were deliberately left unscored rather than guessed at.

C1 Zoonotic potential

Likelihood of transmission from pigs to humans

Highly unlikely: Human infection with the agent has never been reported, or has been reported but is not attributed to pig or pork exposure

CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.

Confirmed by Eric. CONFIRMED. REVIEWED ON C1_C2_RECLASSIFICATION.md, 2026-09-04, after the C1/C2 rewording that separated exposure from consequence. Eric marked up every moved cell and reversed his own earlier setting on twenty of the twenty-one: "In almost every case, I agreed with new opinion and reversed my old setting." HIS MARKUP HERE WAS "l1". Reverses his 2026-09-03 level 2. The folder is three seroprevalence studies and establishes no pig-attributed human case; Q fever is accepted as coming from cattle, sheep and goats.

Basis. THE FOLDER HAS NO DISEASES OF SWINE CHAPTER -- Coxiella burnetii is not covered in the book. It holds three journal papers and nothing else. ferrara_2024: 414 serum samples from 32 COMMERCIAL herds in Campania, southern Italy, tested with commercial multispecies ELISA, 4.1% seropositive for Coxiella, with phase-specific ELISA confirming 12 of 17 positives against phase I or II antigens, "INDICATING THE PRESENCE OF BOTH ACUTE AND CHRONIC INFECTIONS". mcmillan_2024: FERAL swine serosurveillance in Hawaii and Texas, seropositivity 0.19% and 6.03%. mcmillan_2026: the companion study in California feral swine. ALL THREE ARE SEROPREVALENCE STUDIES. None describes clinical disease in a pig, a transmission route into a pig herd, or any US commercial data. On the human disease and the pig link, mcmillan_2024: "Feral swine are invasive in the United States and A RESERVOIR FOR INFECTIOUS DISEASES... FERAL SWINE COULD CONTRIBUTE TO THE SPREAD OF COXIELLA BURNETII, the causative agent of human Q fever... Seropositivity rates were as high as 0.19% and 6.03% in Hawaii and Texas, respectively, INDICATING THAT FERAL SWINE CANNOT BE RULED OUT AS A POTENTIAL RESERVOIR for disease transmission and spread. In Texas, we identified THE OVERLAP BETWEEN SEROPOSITIVITY OF FERAL SWINE AND HUMAN Q FEVER INCIDENCE. These results indicate that there is A POTENTIALLY LOW BUT DETECTABLE RISK of C. burnetii exposure associated with feral swine populations." On the route generally: Q fever is acquired "MOST COMMONLY AFTER EXPOSURE TO CONTAMINATED AEROSOLS", the organism "HAS A VERY LOW INFECTIOUS DOSE, SHOWN TO BE AS LOW AS A SINGLE BACTERIUM", and the small cell variant "IS HIGHLY STABLE IN THE ENVIRONMENT". Q fever was first recognised in ABATTOIR WORKERS in Brisbane in the 1930s.

How this level was decided

MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. The folder is three seroprevalence studies and WHAT IT DOES NOT ESTABLISH IS A SINGLE PIG-ATTRIBUTED HUMAN CASE. The Texas finding is a geographic overlap between feral swine seropositivity and human Q fever incidence, in a state where cattle, sheep and goats are the accepted sources.

PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: INFERRED, AND FLAGGED. LEVEL 2 IS SCORED -- human infection from pigs is plausible but has never been reported, and no control point is implemented against it, which is the label. What the folder establishes is that pigs are exposed, on two continents, in commercial and feral populations, and that the organism they are exposed to causes a human disease acquired by aerosol at a single-organism infectious dose. WHAT IT DOES NOT ESTABLISH IS A SINGLE PIG-ATTRIBUTED HUMAN CASE. The Texas finding is a geographic OVERLAP between feral swine seropositivity and human Q fever incidence, which is an ecological correlation in a state where cattle, sheep and goats are the accepted sources; and the authors' own conclusion is hedged twice over -- pigs "cannot be ruled out", the risk is "potentially" low but detectable. THE ARGUMENT FOR LEVEL 1 is your ruling on Staphylococcus hyicus this evening -- "though isolated from humans rarely IT IS MISLEADING TO CONSIDER IT A CONSEQUENTIAL ZOONOSIS" -- and on Bordetella, where you accepted level 2 on a comparable "plausible but unknown". This is closer to the Bordetella shape than the S. hyicus one, which is why level 2 is scored, but it is your call.

C2 Zoonotic impact

Severity of human illness caused by the agent

Moderate: Clinically important illness is common and may require medical treatment or hospitalization, but death or permanent disability is uncommon

CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.

Confirmed by Eric. CONFIRMED. "c2l3, QF can be a significant pathogen in people"

Basis. THE FOLDER HAS NO DISEASES OF SWINE CHAPTER -- Coxiella burnetii is not covered in the book. It holds three journal papers and nothing else. ferrara_2024: 414 serum samples from 32 COMMERCIAL herds in Campania, southern Italy, tested with commercial multispecies ELISA, 4.1% seropositive for Coxiella, with phase-specific ELISA confirming 12 of 17 positives against phase I or II antigens, "INDICATING THE PRESENCE OF BOTH ACUTE AND CHRONIC INFECTIONS". mcmillan_2024: FERAL swine serosurveillance in Hawaii and Texas, seropositivity 0.19% and 6.03%. mcmillan_2026: the companion study in California feral swine. ALL THREE ARE SEROPREVALENCE STUDIES. None describes clinical disease in a pig, a transmission route into a pig herd, or any US commercial data. On what Q fever is in people, mcmillan_2024: C. burnetii "CAN MANIFEST AS AN ACUTE SELF-LIMITING FEBRILE ILLNESS WITH INFLUENZA-LIKE SYMPTOMS... MORE SEVERE FORMS OF Q FEVER MANIFEST MONTHS TO YEARS AFTER ACUTE INFECTION IN THE FORM OF ENDOCARDITIS, CHRONIC HEPATITIS, OSTEOARTICULAR [disease]." On how much of it is silent: "reported cases likely do not represent the true extent of the disease burden because APPROXIMATELY 60% OF CASES ARE ASYMPTOMATIC." Texas incidence ran between 0.017 and 0.099 reported cases per 100,000 population, 2008 to 2022, with acute and chronic cases tracked separately.

How this level was decided

INFERRED, AND IT MOVES WITH C1. Level 3 -- clinically important illness that may require medical treatment or hospitalization, with death or permanent disability uncommon. Sixty percent of infections are asymptomatic and the acute form is a self-limiting influenza-like illness; the severe form is real but delayed and uncommon. THE ARGUMENT FOR LEVEL 4 is chronic Q fever endocarditis, which is life-threatening and can appear years later, and level 4 asks only for a substantial risk EVEN IF INFECTIONS ARE UNCOMMON. IT IS NOT TAKEN because the folder tracks acute and chronic cases separately and the chronic form is the small share. NOTE THE DEPENDENCY: if you rule C1 to level 1, this cell goes to level 1 with it, not to level 2.

C3 Herd introduction risk

Effort required to keep the agent out of the herd

Housing alone keeps it out: Raising pigs indoors and off soil breaks the cycle, so no ongoing biosecurity program is needed and only outdoor herds stay exposed

Corrected by Eric from no level assigned. Reason: "c3l2, exposure to pigs would in all likelihood need to come from contact with ruminants and moving pigs inside would exclude this"

How this level was decided

NOT ASSESSED. C3 asks what effort would keep this agent out of a US herd, and the folder does not describe a route into one. IT IS TEMPTING TO REACH FOR LEVEL 2 on the general Q fever story -- a ruminant organism, aerosol from parturient animals, so separate the pigs from the ruminants and house them. THE ONE STUDY THAT TESTED THAT HYPOTHESIS FOUND AGAINST IT: farming system and ruminant density did not predict exposure in Italian commercial pigs, only location did. That is weak evidence on seventeen positives, but it is the only evidence there is, and it points away from the answer the pass would otherwise have written. THE ALTERNATIVE READING IS LEVEL 4, on the organism's single-cell infectious dose and windborne environmentally stable spore-like form -- which would mean filtration. Nothing in the folder chooses between level 2 and level 4, and the KISS rule you set on PCV4 applies: where the folder cannot support the claim, the cell stays empty, because a filled-in level is indistinguishable from a real one. YOU CAN CLOSE THIS CELL YOURSELF if you know how Q fever behaves around US herds; that is how the Saint Valerien cell was legitimately filled.

C4 Detection difficulty

Difficulty of recognizing and confirming infection

Reference or research laboratory required: A validated assay exists, but only at a national reference or research laboratory rather than at local or regional level

CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.

Confirmed by Eric. CONFIRMED. "C4l3, i think there is adequate testing methods available, but it would not surprise me that a pig oriented lab would have to send the sample to a reference lab for confirmation"

How this level was decided

INFERRED. Level 3 -- a validated assay exists but at reference or research laboratory level rather than locally. WHAT SUPPORTS IT: commercial multispecies ELISAs exist and worked, and phase I and phase II antigen discrimination is an established technique, so this is not level 4 where no test of known reliability exists. WHAT KEEPS IT OFF LEVEL 2: the kits are MULTISPECIES products validated for ruminants and applied to pigs, all three studies were run in research settings, and C. burnetii is handled under containment. RULE THIS THE WAY YOU RULED other_actinobacillus_species -- "conceivable that many labs could isolate and type to genus level but may likely require assistance from a reference laboratory" -- since it is the same question. If US laboratories will not run Coxiella serology on a pig at all, this is level 4.

C5 Production cost

Financial impact on the infected farm's cost of production

CONFIRMED NOT ASSESSABLE. No level was assigned on this criterion, and Eric has reviewed that and ruled it correct — the folder holds nothing bearing on it. This is a statement about what the evidence supports, not a finding about the agent.

Confirmed by Eric. RULED NOT ASSESSABLE AND CONFIRMED IN THE KISS ROUTE. Against each of these three open cells Eric wrote the single word "KISS", 2026-09-03 -- the same marking he used on porcine_ephemeroviruses_1_and_2. THE PASS HAD ALREADY LEFT THEM NULL, so he is confirming empty cells rather than emptying full ones. COXIELLA BURNETII HAS NO DISEASES OF SWINE CHAPTER; the folder is three seroprevalence papers and nothing else, and none of them describes clinical disease in a pig. C5 is empty because ferrara 2024 declines the claim in the words the criterion needs -- "the impact on pig farms are currently unclear... further studies are necessary to fully understand ... the impact on productivity"; C7 and C8 follow it, because whether a treatment would improve outcomes and whether a vaccine is needed are both claims about a disease nobody has characterised in this species. THE ENTRY IS UNEXPORTABLE, which is the intended outcome. NOTE WHAT HE DID NOT KISS: he filled C3 himself, moving it from null to level 2 on an observation the folder did not contain, and confirmed C1, C2, C4 and C6. The KISS route is being applied cell by cell rather than entry by entry, which is what it is for.

Basis. THE FOLDER HAS NO DISEASES OF SWINE CHAPTER -- Coxiella burnetii is not covered in the book. It holds three journal papers and nothing else. ferrara_2024: 414 serum samples from 32 COMMERCIAL herds in Campania, southern Italy, tested with commercial multispecies ELISA, 4.1% seropositive for Coxiella, with phase-specific ELISA confirming 12 of 17 positives against phase I or II antigens, "INDICATING THE PRESENCE OF BOTH ACUTE AND CHRONIC INFECTIONS". mcmillan_2024: FERAL swine serosurveillance in Hawaii and Texas, seropositivity 0.19% and 6.03%. mcmillan_2026: the companion study in California feral swine. ALL THREE ARE SEROPREVALENCE STUDIES. None describes clinical disease in a pig, a transmission route into a pig herd, or any US commercial data. ferrara_2024 states the gap in its own conclusion: "These pathogens have already been described in the pig population, ALTHOUGH THE DYNAMICS OF THE INFECTION AND THE IMPACT ON PIG FARMS ARE CURRENTLY UNCLEAR... FURTHER STUDIES ARE NECESSARY TO FULLY UNDERSTAND THE DYNAMICS OF THESE INFECTIONS IN PIGS, THE IMPACT ON PRODUCTIVITY, AND THE PUBLIC HEALTH CONSEQUENCES IN THE CASE OF COXIELLA." No clinical sign, lesion, abortion, mortality or performance effect attributable to C. burnetii in a pig is reported in any of the three papers.

How this level was decided

NOT ASSESSED, and the authors decline the claim in the same words the criterion needs. This is the Ebola C5 shape exactly: seroprevalence establishes exposure, and exposure is not disease. IT IS TEMPTING TO SCORE LEVEL 1 -- the pigs were seropositive and nobody reported them sick -- AND THAT IS THE READING TO RESIST. None of these studies looked for disease; they sampled sera. An examined negative is evidence, a silence is not, and level 1 is as much a magnitude claim as level 4. NOTE ALSO THAT COXIELLA IS AN ABORTIFACIENT IN RUMINANTS, so the plausible pig effect is reproductive, and none of the three studies examined reproductive performance.

C6 Market impact

Duration of material disruption to pork and pig markets

Negligible: Little or no material disruption to supply or demand when disease occurs on one or more farms

CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.

Confirmed by Eric. CONFIRMED. "c6l1, i don't think there is any reason to think the market would react. QF doesnt seem to be well adapted to pigs and would be unlikely to present as an outbreak"

How this level was decided

INFERRED. Level 1, on YOUR OWN ANTHRAX REASONING, which is the closest precedent in the register: "ANTHRAX IS WELL KNOWN IN RUMINANT INDUSTRIES SO A DIAGNOSIS IN THE PIG INDUSTRY WOULD LIKELY NOT ATTRACT ANY ATTENTION IN THE MARKET." Q fever is the same shape -- a long-established ruminant zoonosis, notifiable, with an existing public health apparatus, so a detection in pigs would be a variation on a known theme rather than a novel event. THIS IS WHY THE CELL IS SCORED RATHER THAN NULLED under the standing note SCORING/market_impact: the note reserves a null for where NOTHING has ever been observed, and here the agent is already in US animals with human cases counted every year and no market consequence anywhere.

C7 Treatment potential

Potential for treatment to improve outcomes

Confirmed by Eric. RULED NOT ASSESSABLE AND CONFIRMED IN THE KISS ROUTE. Against each of these three open cells Eric wrote the single word "KISS", 2026-09-03 -- the same marking he used on porcine_ephemeroviruses_1_and_2. THE PASS HAD ALREADY LEFT THEM NULL, so he is confirming empty cells rather than emptying full ones. COXIELLA BURNETII HAS NO DISEASES OF SWINE CHAPTER; the folder is three seroprevalence papers and nothing else, and none of them describes clinical disease in a pig. C5 is empty because ferrara 2024 declines the claim in the words the criterion needs -- "the impact on pig farms are currently unclear... further studies are necessary to fully understand ... the impact on productivity"; C7 and C8 follow it, because whether a treatment would improve outcomes and whether a vaccine is needed are both claims about a disease nobody has characterised in this species. THE ENTRY IS UNEXPORTABLE, which is the intended outcome. NOTE WHAT HE DID NOT KISS: he filled C3 himself, moving it from null to level 2 on an observation the folder did not contain, and confirmed C1, C2, C4 and C6. The KISS route is being applied cell by cell rather than entry by entry, which is what it is for.

How this level was decided

NOT ASSESSED, AND IT MOVES WITH C5. C7 asks whether outcomes would meaningfully improve if a treatment existed, and no outcome has been attributed to this agent in a pig -- so there is nothing to improve and nothing to rule out. SCORING LEVEL 1 WOULD ASSERT THAT PIGS RECOVER ACCEPTABLY WITHOUT TREATMENT, which nobody has established, and your 2026-09-02 rule forbids the other easy answer, that nobody treats what nobody diagnoses. If you fill C5, fill this with it.

C8 Vaccine availability

Availability of effective vaccines or bacterins

Confirmed by Eric. RULED NOT ASSESSABLE AND CONFIRMED IN THE KISS ROUTE. Against each of these three open cells Eric wrote the single word "KISS", 2026-09-03 -- the same marking he used on porcine_ephemeroviruses_1_and_2. THE PASS HAD ALREADY LEFT THEM NULL, so he is confirming empty cells rather than emptying full ones. COXIELLA BURNETII HAS NO DISEASES OF SWINE CHAPTER; the folder is three seroprevalence papers and nothing else, and none of them describes clinical disease in a pig. C5 is empty because ferrara 2024 declines the claim in the words the criterion needs -- "the impact on pig farms are currently unclear... further studies are necessary to fully understand ... the impact on productivity"; C7 and C8 follow it, because whether a treatment would improve outcomes and whether a vaccine is needed are both claims about a disease nobody has characterised in this species. THE ENTRY IS UNEXPORTABLE, which is the intended outcome. NOTE WHAT HE DID NOT KISS: he filled C3 himself, moving it from null to level 2 on an observation the folder did not contain, and confirmed C1, C2, C4 and C6. The KISS route is being applied cell by cell rather than entry by entry, which is what it is for.

How this level was decided

NOT ASSESSED, AND IT MOVES WITH C5, under the rule you imposed on pasivirus_a and again on pcv4: ASSERTING THAT A VACCINE IS NOT NEEDED IS STILL A CLAIM ABOUT THE DISEASE, and it cannot be made for an agent whose disease-causing potential in pigs is unknown. That is precisely this entry -- the one study of commercial pigs says the impact on pig farms is currently unclear. THE FOUR NULLS ON THIS ENTRY MAKE IT UNEXPORTABLE, which is the intended outcome and is what the KISS route is for. It joins the eleven already there.

Levels and evidence are generated from data/assignments/coxiella_burnetii.yml; the overview is authored in data/overviews/coxiella_burnetii.md. Do not hand-edit this page — corrections go in data/assignments/CORRECTIONS.yml.

Quoted material marked Basis is from Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, Zhang J, eds. Diseases of Swine, 12th edition. Hoboken: Wiley Blackwell, 2025 — except where another source is named in the quotation itself.

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