Clostridioides difficile
LEVELS: Highly unlikely; Moderate; Already in the herd; Laboratory-dependent; Minor; Negligible; Some; Needed but not available
| Register id | clostridioides_difficile |
| Type | bacteria |
| Scientific name | Clostridioides difficile |
| NCBI taxid | 1496 |
| Evidence | 1 document(s) |
| Assigned | 2026-09-04, against criteria version 093366e352a2 |
Overview
Clostridioides difficile is a spore-forming anaerobe that causes a necrotising inflammation of the caecum and colon in piglets in their first week of life. Unlike the disease in people and most other species, it is not associated with antibiotic use in pigs. Affected piglets scour, may show laboured breathing and abdominal swelling, and can die suddenly; the classic lesion is a swollen mesocolon with small volcano-like eruptions of pus through the gut lining. Colonisation is near-universal in newborn piglets — effectively 100% by three days of age — but falls away sharply as pigs get older, so finding the organism is not the same as diagnosing the disease. The spores are highly resistant, survive most common disinfectants and are everywhere faeces are. Ribotype 078, the type most often found in pigs, is also one of the commonest causes of multidrug-resistant human disease, which has raised the question of a link — but direct transmission from pigs to people has never been demonstrated, and human disease is far too widespread to be explained by pig contact. No commercial swine vaccine exists.
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, and he supplies the argument the pass could not make. "c1l1, disease is well established in humans, well beyond the popoulation of humans that has anything exposure to pigs. L1 until further evidence arrives to make the connection between pigs and people - possible i suppose that people are the source of infection for pigs." THE PASS HAD CALLED THIS THE CLOSEST CALL IN THE BATCH, because pigs are a reservoir of ribotype 078 and ch47 records "genetically indistinguishable strains have been detected both in pigs and humans, including samples from farm workers" -- one step short of attribution. His answer is that the human disease is far too widespread to be explained by pig contact, so shared strains show a shared organism rather than a pig source, AND THAT THE ARROW MAY POINT THE OTHER WAY. That is the same reverse-zoonosis reading he applied to swine papillomavirus, where human papillomavirus in pig slurry turned out to be human sewage in the pit.
Basis. ch47 47.2.3.2: "Toxigenic strains of C. difficile are common in pigs, cattle, poultry, dogs, and a variety of other mammals. Contamination of carcasses at slaughter is uncommon, and foodborne transmission is unlikely. Direct transmission from human carriers or from infected animals has also not been confirmed as a direct cause of CDAD. C. difficile ribotype 078 is among the most commonly isolated strains in cases of multidrug-resistant, nosocomial, and CA-CDAD in humans. Pigs are a reservoir of this ribotype, and genetically indistinguishable strains have been detected both in pigs and humans, including samples from farm workers."
How this level was decided
MOVED L2 -> L1, re-read 2026-09-04 AGAINST THE REWORDED LABELS. FLAG. ch47 47.2.3.2: "Direct transmission from human carriers or from infected animals HAS ALSO NOT BEEN CONFIRMED as a direct cause of CDAD", carcass contamination uncommon, foodborne transmission unlikely. THE COUNTER-ARGUMENT IS UNUSUALLY STRONG and this is the closest call in the batch: pigs are a reservoir of ribotype 078 and "genetically indistinguishable strains have been detected both in pigs and humans, including samples from farm workers". Indistinguishable strains in exposed workers is one step short of attribution.
PREVIOUS ANSWER, kept because the evidence behind it has not changed, only the level boundary: Level 2, and the chapter argues both sides of it in one paragraph. For: pigs are a reservoir of ribotype 078, a major human strain, and genetically indistinguishable isolates have been recovered from pigs and from farm workers. Against: carcass contamination is uncommon, foodborne transmission is called unlikely, and direct transmission has never been confirmed. So pig-to-human infection is plausible and has not been demonstrated, and no control point in pork production is directed at it -- both clauses of level 2. It is not level 3, because level 3 needs a KNOWN risk that follows the failure of a named control point, and the chapter says the source of community-acquired cases is usually unknown.
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, agree with assessment. Also is consistent with C1l2 because pigs don't actually seem to be source for most human cases but it is at least plausible."
Basis. ch47 47.2.3.2: "CDAD is the leading cause of antibiotic-associated diarrhea in humans, characterized by syndromes from mild diarrhea to fatal pseudomembranous colitis." "C. difficile ribotype 078 is among the most commonly isolated strains in cases of multidrug-resistant, nosocomial, and CA-CDAD in humans." "CA-CDAD occurs in young persons without contact with hospital or clinical environments."
How this level was decided
Level 3. Clinically important illness is common, hospitalisation is the norm for severe cases and the disease is a leading cause of antibiotic-associated diarrhoea. FLAGGED as a level 3 or 4 judgment. Fatal pseudomembranous colitis is named in the chapter and argues level 4 -- but the deaths concentrate in elderly hospitalised patients with the nosocomial form, and the form the chapter links to pigs is community-acquired disease in young people, where recovery is the rule. Scored on the pig-linked form.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Already in the herd: Present in most herds, or carried by pigs themselves, so there is no introduction event to prevent
Basis. ch47 47.2.3.1: "The organism can be isolated from the intestinal content of piglets as early as 1 hour after birth, and 100% of piglets are positive by 3 days postpartum." "The primary source of infection for newborn pigs is spores shed in sow feces or in the contaminated local environment." "its highly resistant spores are ubiquitous in the environment" and "are resistant to most common disinfectants, which makes them a sturdy environmental contaminant." "The prevalence of C. difficile is high in neonatal pigs, significantly decreases with age, and is unaffected by antimicrobial use in pigs of all ages."
How this level was decided
Level 1, and it is about as clean as level 1 gets: every piglet is colonised within three days of birth, from the sow and from an environment whose spores resist most disinfectants. There is no introduction event to prevent because the agent is already there before the pig is a day old. Note that this is a different situation from C. perfringens type C in the same chapter, which is only occasionally normal flora and is scored at level 4 -- the distinction is 100% colonisation by day 3 against "albeit rarely, in low numbers".
C4 Detection difficulty
Difficulty of recognizing and confirming infection
Laboratory-dependent: The presentation does not point to this disease specifically, but local or regional laboratories can confirm it with a validated assay once it is suspected
Basis. ch47 47.2.3.4: "Gross lesions are nonspecific." "Microscopic lesions of CDAD in pigs are limited to the cecum and colon and may be very characteristic but are not specific." 47.2.3.5: "mesocolonic edema and necrosuppurative typhlocolitis with volcano lesions are highly suggestive of CDAD in piglets. However, a definitive diagnosis of C. difficile infection must be based on detection of TcdA, TcdB, or both in feces or colonic contents. The reference method is measurement of neutralizable cytotoxicity in monolayers of Chinese hamster ovary or other cells, but most laboratories now use commercially available enzyme immunoassays." "Culture of C. difficile is of little diagnostic significance because the prevalence of C. difficile in the intestinal tract of healthy piglets is relatively high."
How this level was decided
Level 2. The presentation does not point here -- early-onset scours in a one-week-old piglet has a long differential, and the chapter says gross lesions are nonspecific -- so level 1 is out. But the confirmatory test is a commercially available toxin enzyme immunoassay that most laboratories run, which is level 2 exactly. NOTE the interpretive trap the chapter records: toxin must be read alongside clinical and post-mortem findings, because TcdA and TcdB have been found inconsistently in normal piglets, and culture alone means nothing because colonisation is universal.
C5 Production cost
Financial impact on the infected farm's cost of production
Minor: Small and generally short-lived losses with little effect on overall cost of production
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c5l2, clinical impact seems to vary by farm but in general, is a minor cost to production"
Basis. ch47 47.2.3: "In pigs, CDAD is not antibiotic-associated and typically presents at 1-7 days of age as diarrhea and rarely as respiratory distress or sudden death." 47.2.3.1: prevalence "decreases dramatically in nursery-age and older pigs, ranging between 3 and 9%". 47.2.3.4: piglets present "with a history of early-onset scours and rarely with respiratory distress, mild abdominal distension, scrotal edema, or sudden death".
How this level was decided
INFERRED -- the chapter gives colonisation rates but no rate of DISEASE, no mortality figure and no cost. What it does establish is that colonisation is universal while clinical disease is a subset, that the presentation is scours rather than death, and that the window is one week wide and closes on its own as the microbiota matures. Small losses in the farrowing house. Level 2 under the standing note SCORING/production_cost_impact.
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, old disease with no evidence to suggest diagnosis would impact markets"
Basis. Section 47.2.3 records no trade measure, movement control or consumer response. The organism is present in 100% of piglets by three days of age and is described as a common contaminant of manured soil, meats and vegetables.
How this level was decided
INFERRED. Under the standing note SCORING/market_impact this is an agent universally present in US pigs and long recognised, with no historical market move on record. NOTE the one thing that could change that, recorded because it is the kind of tail Eric drew a boundary around on Campylobacter: the chapter names pigs as a reservoir of ribotype 078 and reports genetically indistinguishable strains in pigs and farm workers. A confirmed pork-to-human CDAD event would be a new fact, not a repeat of an old one. Level 1 records what has happened, not what could.
C7 Treatment potential
Potential for treatment to improve outcomes
Some: Treatment exists but is inconsistent, requires extralabel use, or works only in some circumstances
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c7l2, extralabel treatments available with variable efficacy"
Basis. ch47 47.2.3.6: "Results of in vitro antimicrobial susceptibility testing suggest that tylosin may be effective in treatment of piglets with CDAD." "Administration of the nontoxigenic strain of C. difficile Z31 reduces the incidence of infection and the intensity of neonatal diarrhea; therefore, this method has been proposed as a preventive measure in the absence of a commercially available vaccine."
How this level was decided
INFERRED. The chapter offers one candidate treatment, tylosin, and supports it only with in vitro susceptibility -- no clinical trial, no labelled indication. That is treatment that exists but is inconsistent and would be extralabel, which is level 2 under the standing note SCORING/treatment_potential. It is not level 3, because a preventive that works is on the record: the nontoxigenic Z31 strain reduces both incidence and severity.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Needed but not available: No effective vaccine is available in the US or has been developed, and the disease would justify vaccinating if one existed
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "c8l3, seems as though there would be a demand for an effective vaccine on at least some farms, especially given variable efficacy of treatments"
Basis. ch47 47.2.3.6: "Immunoprophylaxis of CDAD in domestic animals has not been studied widely, but precedent in other species suggests that immunity will be antitoxic. Antibodies against TcdA and TcdB prevent toxin binding in mouse and hamster models, eliminating secretion, inflammation, and clinical disease." Administration of nontoxigenic strain Z31 "has been proposed as a preventive measure in the absence of a commercially available vaccine".
How this level was decided
INFERRED, AND FLAGGED AS THE ONE MOST LIKELY TO COME BACK DOWN. No vaccine exists -- the chapter says so in those words -- and under the reworded criterion the question is whether one is warranted. The argument for level 3 is that this is a recognised cause of neonatal scours in every US farrowing house, that the target is demonstrably tractable since antitoxin antibodies abolish disease in animal models, and that the sibling agent in the same chapter is controlled by exactly such a toxoid. The argument against is Eric's own C8 pattern: he has moved eleven entries down to level 1 while explaining that no vaccine was NEEDED, and CDAD is a self-limiting week of scours in a proportion of litters rather than the 100% litter mortality that justifies the type C toxoid. If he rules level 1, the reason will be that the disease does not economically justify vaccinating.
Levels and evidence are generated from data/assignments/clostridioides_difficile.yml; the overview is authored in data/overviews/clostridioides_difficile.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.