Open Outbreak

Salmonella

Also known as: salmonellosis, Salmonella enterica, non-typhoidal Salmonella, NTS

Salmonella is a group of bacteria that can cause salmonellosis, a common foodborne infection. People usually get it by swallowing contaminated food, especially foods from animals, or by contact with infected animals. Most illness is limited to the gut and causes diarrhoea, fever, stomach cramps, and sometimes vomiting. In many people it gets better on its own, but infants, older adults, and people with weak immune systems are more likely to become seriously ill or dehydrated. Some Salmonella infections spread beyond the gut into the blood; those invasive infections are much more dangerous and are linked to antimicrobial resistance in some settings. WHO outbreak notices show that Salmonella can also spread through widely distributed products such as chocolate and infant formula, leading to international recalls. In the sources used here, no reliable general-population R0 estimate was given. Treatment is mainly fluids for uncomplicated illness, with antibiotics reserved for severe or invasive disease; resistance is an important concern. I did not identify a licensed human vaccine for routine use against non-typhoidal Salmonella in the sources retrieved for this page.

Key facts

TransmissionMainly by swallowing contaminated food; also through contact with infected animals or contaminated environments.
Incubationunknown
Case fatalityunknown for routine gastroenteritis in the sources used here; invasive Salmonella infections are described as having a high case fatality ratio.
Reproduction numberunknown
VaccineNo licensed human vaccine for routine prevention of non-typhoidal Salmonella was identified in the sources retrieved here.
TreatmentUsually supportive care such as rehydration; antimicrobials are used for severe or invasive infection, but resistance has emerged.
ReservoirAnimals are an important reservoir; chicken is noted as a major source in humans.
Endemic regionsWorldwide.

Transmission

Salmonella usually spreads when a person swallows the bacteria in contaminated food. The overview source describes salmonellosis as a common form of food poisoning and says many human infections come from animals, with chicken as a major source. WHO outbreak notices show how this can happen in real life: one multinational outbreak was linked to chocolate products distributed to at least 113 countries, and another WHO notice involved infant formula. These events show that spread is often through a contaminated food product rather than direct person-to-person transmission. The sources retrieved for this page did not provide a reliable general-population reproduction number, so that remains unknown here. In public health terms, the main transmission concern is contamination somewhere along the food chain, followed by broad product distribution.

Symptoms and severity

Typical salmonellosis affects the gut. The overview source lists diarrhoea, fever, abdominal cramps, and vomiting as common symptoms. WHO says Salmonella infections are typically mild and often do not require treatment, but it also warns that children and older people are at greater risk of severe complications related to dehydration. That matters because even a short diarrhoeal illness can become dangerous if fluid loss is not replaced, especially in infants or frail adults. A separate review on invasive Salmonella infections describes bloodstream infection as an important problem in low-resource settings and says it may be associated with a high case fatality ratio. The sources used here did not give a single overall fatality percentage for all Salmonella illness, so that figure is listed as unknown. Severity therefore ranges from self-limited diarrhoea to dangerous invasive disease.

Treatment and vaccines

For most uncomplicated Salmonella gastroenteritis, treatment is supportive. WHO states that infections are typically mild and do not require treatment, although people at higher risk may need medical care for dehydration. For severe disease, or when Salmonella invades the bloodstream, antimicrobials are used. The clinical review retrieved here says antimicrobial management is central for invasive Salmonella infections, but it also reports that resistance has emerged to older first-line drugs and that decreased fluoroquinolone susceptibility has been seen. That makes laboratory testing and local guidance important where severe infection is suspected. On vaccines, I did not identify evidence in the retrieved sources for a licensed human vaccine for routine prevention of non-typhoidal Salmonella. The vaccine-related source discusses vaccines as an area of interest in the broader fight against antimicrobial resistance, but it does not provide evidence here of a routine licensed vaccine for this disease.

Where it occurs

Salmonella occurs worldwide. The global burden paper on foodborne disease shows that illness and death from contaminated food are a worldwide public-health problem, and Salmonella is one of the major foodborne hazards included in that assessment. European zoonoses reports in the retrieved literature show salmonellosis as one of the most commonly reported zoonotic infections in Europe, which supports its broad geographic presence rather than restriction to one region. At the same time, the more dangerous invasive forms are especially emphasized in low-resource settings in the clinical review, suggesting that the heaviest burden of severe disease may fall unevenly across regions. WHO outbreak notices also show that a contaminated product can create cases across many countries very quickly. For readers, the simplest picture is this: Salmonella is not confined to one climate zone or continent, and risks exist wherever food production, handling, or distribution allows contamination.

Recent history

In the WHO Disease Outbreak News archive results retrieved for this page, Salmonella appeared in three notices: 2004-06-02 in the United States, 2017-12-22 in France, and 2022-04-27 as a multi-country outbreak linked to chocolate products in Europe and the United States. That is not a large archive count compared with some epidemic diseases, but the notices are important because they show repeated international food-safety events over time. The 2022 WHO notice reported 151 genetically related cases across 11 countries and described a global product recall after the implicated chocolate had been distributed to at least 113 countries. The 2017 WHO notice on Salmonella Agona linked to infant formula highlighted the particular risk to infants. Together, these events suggest a pattern driven less by sustained person-to-person spread and more by contaminated products that move across borders through trade and distribution networks.

What to watch

The main warning signs are changes that make Salmonella harder to contain or more dangerous. One is outbreaks appearing in new countries through widely distributed foods, as seen in the WHO notices on chocolate and infant formula. Another is any clear rise in severe invasive disease, especially bloodstream infection, because the review retrieved here links invasive Salmonella with high case fatality and highlights the difficulty of distinguishing it from other febrile illnesses in some settings. Drug resistance is another key signal: the literature reports resistance to older first-line drugs and reduced susceptibility to fluoroquinolones, so reports of broader resistance or treatment failure would be especially concerning. Finally, public-health agencies would watch for stronger evidence of sustained person-to-person spread in community settings, which is not the usual pattern described in the sources used here. Vaccine availability would also matter if a licensed human vaccine for non-typhoidal Salmonella becomes established.

Related outbreaks

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