Salmonella enterica serogroup B (enteric salmonellosis)
LEVELS: Sometimes occurs; Moderate; Routine biosecurity keeps it out; Laboratory-dependent; Minor; Negligible; Little; Available but inconsistent
| Register id | salmonella_typhimurium |
| Type | bacteria |
| Scientific name | Salmonella enterica subsp. enterica serovar Typhimurium |
| NCBI taxid | 90371 |
| Evidence | 3 document(s) |
| Assigned | 2026-09-06, against criteria version 093366e352a2 |
Overview
This entry covers the enteric salmonellae of pigs, principally Salmonella Typhimurium and the closely related monophasic variant I 4,[5],12:i:-. Unlike the host-adapted Choleraesuis, these cause enterocolitis — diarrhoea rather than septicaemia — and their greater significance is as a food safety problem. Pigs carry them in the intestine, shed them in faeces, and the same serotypes and genotypes predominate in pigs and in human infections. The organisms persist well in the environment and travel efficiently in feed, on fomites and via insects, so colonisation is difficult to prevent altogether. Clinical disease, though, is much less common in modern US production than the literature suggests: confinement housing and slatted floors limit the faecal-oral cycling, and acute outbreaks usually follow a lateral introduction and are resolved by treatment, all-in/all-out movement and cleaning. The practical objective on most farms is therefore to reduce carriage going to slaughter rather than to treat sick pigs.
C1 Zoonotic potential
Likelihood of transmission from pigs to humans
Sometimes occurs: Known risk of transmission to humans (foodborne or occupational), but requires failure of one or more control points for transmission to humans
Basis. "swine colonized or infected with Salmonella are a concern for two major reasons: clinical disease in pigs (salmonellosis) and contamination of pork products that serve as a transmission source for human foodborne illness." "I 4,[5],12:i:- increased in swine but human illness associated with foodborne transmission of this serovar has also increased." (ch53) shic_2021_salmonella: "Nontyphoidal Salmonella are a leading cause of foodborne infections in humans. Animals are reservoirs for many salmonellae, including Salmonella 1,4,[5],12:i:-, an emerging serotype in swine." "Incidence of S. 1,4,[5],12:i:- has increased dramatically in recent years, and many isolates from pigs, pork, and humans are highly related."
How this level was decided
Re-read against the corrected "from pigs" label on 2026-08-27; level 3 unchanged, and this is the cleanest example of what level 3 means. The route is pork -- pigs are the source, not a bystander -- and it is interrupted in practice by slaughter hygiene, processing controls and cooking. Transmission occurs when those control points fail, which is the level 3 definition word for word. Level 3 confirmed, and the genomic point is the strongest support the folder holds: isolates from pigs, pork and humans are highly related, which is attribution rather than association.
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
Basis. "In the United States, an estimated 1.35 million human illnesses occur annually, resulting in approximately 400 deaths and an economic burden of $4.1 billion." "Severe disease and mortality can occur in infants, the elderly, or immunocompromised individuals." (ch55 §55.3) shic_2021_salmonella: "Salmonella spp., including S. 1,4,[5],12:i:-, mainly cause gastroenteritis in humans. Less commonly, systemic disease and extra-intestinal infections occur." "The most common resistance phenotype is ASSuT... Resistance to other antimicrobials has also been documented including quinolones, extended-spectrum beta-lactams, phenicols, and colistin."
How this level was decided
Clinically important illness, commonly requiring medical attention, with 400 deaths against 1.35 million cases -- so death is a real but uncommon outcome. That is level 3 rather than level 4. Level 3 held. Gastroenteritis alone would read as level 2, but multi-drug resistance including to quinolones, extended-spectrum beta-lactams and colistin is what makes an ordinarily self-limiting infection one that may need hospitalisation -- the same reasoning as Eric's S. aureus ruling, where the level turned on the resistant fraction.
C3 Herd introduction risk
Effort required to keep the agent out of the herd
Routine biosecurity keeps it out: Quarantine of incoming stock, transport and fomite control, cleaning and disinfection, and the usual monitoring reliably exclude it
Basis. "A common reservoir for Salmonella is the intestinal tract of warm- and cold-blooded animals." "Salmonella has many attributes necessary to ensure wide distribution, including abundant reservoir hosts, efficient fecal shedding from carrier animals, persistence within the environment, and the effective use of transmission vectors (feed, fomites, insects, etc.)." (ch55 §55.4) shic_2021_salmonella: "Swine are also subclinical carriers of S. 1,4,[5],12:i:- and many other Salmonella serotypes. In carrier animals, shedding is exacerbated by stress including commingling, transport, and food deprivation." "Carrier pigs are an important source of infection. However, the value of serological testing is unclear since antibody response and shedding on the farm are not predictive."
How this level was decided
MOVED L5 -> L3 on 2026-09-03, when C3 was reduced to four levels and the whole level 5 block was re-read against the exclusion test rather than the reservoir test. Eric: "C3 is about exclusion, not reservoirs per se, though the two are related", and "who cares about reservoirs? Reservoirs really don't matter as long as you keep domestic pigs from becoming infected through biosecurity implementation." THE PREVIOUS LEVEL WAS NEVER JUDGED: this entry carried a RENUMBERED L4 -> L5 stamp from 2026-09-01, meaning it was moved past the newly created housing level rather than assessed against it. rodents, birds, feed and fomites -- and Salmonella Choleraesuis is already the worked example at level 3, so this entry sitting two levels above its sibling was an inconsistency in the register.
EARLIER REASONING, kept because it is the evidence read: RENUMBERED L4 -> L5 on 2026-09-01, when C3 went from four levels to five. The argument below is unchanged and so is the judgment. What changed is the scale it sits on. C3 now runs on the EFFORT REQUIRED TO EXCLUDE: L1 already in the herd, L2 housing alone keeps it out, L3 routine biosecurity keeps it out, L4 extraordinary biosecurity required, L5 exclusion may not be achievable. Reservoirs outside the pig industry -- other animal species, insects and the environment itself -- give continuous opportunity for exposure that on-farm biosecurity cannot close. NOTE: this is the case Eric flagged for testing. He expected S. Choleraesuis at level 2 and the other Salmonella entries at level 4, and this entry is the enteric serogroup, so level 4 matches his expectation. Level 3 confirmed. The route is carrier pigs, so housing does nothing -- not level 2 -- and control is quarantine and transport management, which is the routine list. Not level 4 despite the carrier problem, because the factsheet says serological testing is of unclear value, so the expensive carrier-detection programme that defines level 4 is not even on offer.
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
CONFIRMED by Eric. The assignment reached this level from the evidence, and he has reviewed and ratified it.
Confirmed by Eric. CONFIRMED. "l2, straightforward to diagnose"
Basis. "Further delineation of the subspecies is determined by serogrouping and serotyping of Salmonella isolates... usually determined by agglutination-based assays or DNA sequencing." "Pigs with undetectable shedding of Salmonella can begin shedding within hours of applied stress." (ch55 §55.2, §55.4.2)
How this level was decided
Culture is routine regional-laboratory work, but intermittent shedding means a negative result does not clear an animal, and clinical signs overlap other enteric disease. Laboratory-dependent rather than routine. Unchanged. Routine culture and serotyping.
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
Corrected by Eric from L1 Negligible. Reason: MOVED L1 -> L2. "c5l2, i am upgrading because when the clincial diseaese does occur, it is certainly higher than negligible, question is whether it should be l2 or l3 but we will go with l2 because no recent data describing industr prevalence of clincial disease due to the agent." The cell was flagged because it sat BELOW the level his own standing note implies -- that note identifies short-lived Salmonella losses as level 2 -- and this settles that the reasoning does reach this entry. Note he named the L2/L3 boundary as the open question and chose L2 for want of recent US prevalence data, not because the disease is mild.
Basis. Eric, 2026-08-27: "modern production systems in the US do not facilitate this disease persisting clinically due to confinement environment and perforated flooring. Acute insults I think are often due to a lateral introduction, that is then managed by treatment followed by all-in all-out movement, and cleaning & disinfection... So the losses are short-lived rather than merely manageable." Against that, CFSPH 2013 states that "Clinical cases are common in cattle, pigs and horses", that "Chronic enteritis is mainly seen in older calves, adult cattle and growing pigs", and that "Rectal strictures can be sequelae in growing pigs". shic_2021_salmonella: "The main serotypes associated with clinical salmonellosis in pigs are S. Typhimurium and S. 1,4,[5],12:i:-. Enterocolitis and septicemia can be seen. Most pigs recover but they may shed bacteria for months after resolution of clinical signs."
How this level was decided
MOVED L3 -> L1, and this cell is where the new standing note and the new document pull against each other -- FLAGGED so the tension is visible rather than resolved silently. The CFSPH factsheet describes common clinical salmonellosis with chronic sequelae in growing pigs, which read alone supports level 3. The standing note SCORING/production_cost_impact says to score modern US production rather than the literature, and it exists precisely because disease chapters and factsheets describe severity that US confinement has engineered out. Eric supplied the mechanism, and his final clause is a level test rather than colour: short-lived losses are level 2, merely manageable losses are level 3, and he placed this below both at level 1. Scored to his note. NOTE FOR HIM: this is the first cell where following the note means scoring against a document in the folder, which is exactly what the note directs but is worth seeing once. LEVEL 1 HELD, AND FLAGGED against Eric's own standing note. The note's Salmonella passage supplies a level test in his words -- modern US systems do not let the disease persist clinically, an acute insult is managed by treatment then all-in all-out and C&D, "so the losses are short-lived rather than merely manageable", which he identifies as LEVEL 2 rather than 3. This cell sits at 1, below that. The factsheet describes clinical enterocolitis and septicaemia with recovery, which reads as a real if short-lived insult. Whether his Salmonella reasoning was meant to reach this entry or only salmonella_choleraesuis is his to say.
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. "c6l1, enteric salmonellae are occassionally diagnosed in individual pigs or herds but are treated like any other endemic pathogen, and they are only rarely recovered from near market pigs because they almost never cause clinical disease in anything other than neonates or juveniles. The market is unlikely to react to a diagnosis, in the absence of a major foodborne outbreak in people that was tied to pigs." [MERGED 2026-09-01. This cell had been recorded twice and YAML was silently keeping only this copy. Eric stated the same ruling on an earlier sheet, 2026-08-26, in these words: "should be C6L1 - enteric salmonellosis would be unlikely to have any effect on market."]
Basis. CFSPH 2013 records no trade measure or movement control following a swine Salmonella diagnosis. Eric, 2026-08-27: "enteric salmonellae are occassionally diagnosed in individual pigs or herds but are treated like any other endemic pathogen... The market is unlikely to react to a diagnosis, in the absence of a major foodborne outbreak in people that was tied to pigs." shic_2021_salmonella: "Salmonellosis is not an OIE-listed disease in pigs."
How this level was decided
MOVED L2 -> L1 under the standing note SCORING/market_impact. Salmonella is endemic and routinely diagnosed in US pigs with no historical market move, which is the test the note sets. He drew the boundary himself on Campylobacter: a major multistate foodborne outbreak traced to pork "is the 95% percentile issue and abnormal", so the tail does not set the score. Level 1 confirmed on a direct statement.
C7 Treatment potential
Potential for treatment to improve outcomes
Little: Effective pathogen-directed treatment is available and works, or animals recover acceptably without it
Basis. "The Centers for Disease Control and Prevention (CDC) has classified antibiotic-resistant Salmonella as a serious threat." The chapter's control discussion assumes antimicrobial treatment of clinical cases is available. (ch55 §55.3, §55.8.2) shic_2021_salmonella: "Antimicrobial treatment is indicated for pigs with clinical signs and lesions suggestive of salmonellosis. Treatment regimens should be based on antibiograms, especially for emerging serotypes like S. 1,4,[5],12:i:- that often demonstrate multi-drug resistance."
How this level was decided
Antimicrobial treatment is available and used for clinical salmonellosis. Resistance is a serious and worsening problem, which argues for level 2, but the criterion asks whether better treatment would improve outcomes -- and for most clinical cases current treatment works. Level 1 confirmed. Treatment is indicated and used, which is the labelled-product half of level 1. The resistance caveat is a reason to choose the drug on an antibiogram, not evidence that treatment is unavailable.
C8 Vaccine availability
Availability of effective vaccines or bacterins
Available but inconsistent: Commercial or autogenous vaccines exist in the US but protection may be inconsistent
Basis. "Pig resistance to Salmonella can be enhanced by proper hygiene, appropriate nutrition, and disease prevention, including vaccination against Salmonella." "In Salmonella, LPS and flagella are immune-dominant as well as immune-variable components that challenge vaccine design." (ch55 §55.8.1, §55.2)
How this level was decided
Vaccines exist and are used, and the chapter states directly that antigenic variability challenges vaccine design -- which is inconsistent protection, the level 2 definition. Unchanged. Level 2: Salmonella vaccines including autogenous products are used in swine with variable effect.
Levels and evidence are generated from data/assignments/salmonella_typhimurium.yml; the overview is authored in data/overviews/salmonella_typhimurium.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.