August 18, 2026

expert reaction to UK Salmonella outbreak

Scientists comment on a Salmonella outbreak in the UK announced in a report from the UK Health Security Agency (UKHSA).

Prof Owen B Spiller, Head of Medical Microbiology at Cardiff University’s Division of Infection & Immunity, said:

“Here are my thoughts on the current UK outbreak. Even though I have an honorary consulting contract with UKHSA, I should emphasise that I have not directly been involved in this investigation!

“Large Salmonella outbreaks affecting several countries are not unprecedented. In 2020, the European Centre for Disease Prevention and Control and the European Food Safety Authority reported 1,656 confirmed or probable cases of Salmonella Enteritidis across 18 European countries, including retrospectively identified cases dating back to 2012 (https://doi.org/10.2903/sp.efsa.2020.EN-1799).

“Whole-genome sequencing divided the bacteria responsible for that outbreak into two closely related but distinguishable groups, labelled t5.175 and t5.360 (https://doi.org/10.4315/JFP-21-096). The “t5” designation means that the bacteria were grouped using a threshold of five single-letter differences in their DNA. In everyday terms, genetic sequencing identified two very close branches of the same family tree, rather than a collection of distant relatives. The epidemiological and food-chain investigations linked that prolonged outbreak to eggs originating from Poland.

The current UK outbreak belongs to a different genetic cluster, called t5.9411. As of 13 August, UKHSA had identified 207 patients whose infections occurred between August 2025 and August 2026. Cases have so far been detected only in the UK, but UKHSA has alerted other European countries so that they can look for genetically related infections. The t5.9411 designation shows that it is not part of either of the earlier t5.175 or t5.360 clusters, although a cluster number by itself cannot establish where a strain originated. UKHSA has reported a slightly more distant genetic relationship to a separate 2025 outbreak that was linked to imported eggs.

While not yet proven, imported eggs are proposed as the leading suspect as a source, and while proper cooking of food easily kills Salmonella, it is the contamination of cooking surfaces during food preparation that is likely causing this sustained level of cases. Cases are spread out across the UK geographically and evidence suggests eating out rather than home-cooked meals as the setting for public exposure to these bacteria.

Most Salmonella infections resolve without antibiotics, but the severity of this outbreak should not be understated. Among patients for whom hospitalisation information was available, 38% were admitted to hospital. Two developed bloodstream infections and one death has been associated with the outbreak.

Treatment for most patients consists of fluids and rest. Antibiotics are generally reserved for severe or invasive infection and for people at greater risk of complications, including very young children, older people and those with underlying medical conditions. UKHSA has not published antibiotic-susceptibility results for this outbreak, but recent European data show that only about 1% of Salmonella infections are resistant to the first-choice antibiotic in a hospital setting.

This differs from our work with Médecins Sans Frontières among severely malnourished children in Niger. In that very different clinical setting, 95% of the viable bloodstream isolates tested were resistant to local first-choice antibiotics, although susceptibility to third-generation cephalosporins commonly used in the UK was retained. We also found antibiotic resistance genes carried on mobile plasmids capable of rapidly moving between bacteria (https://doi.org/10.1099/mgen.0.001788). This illustrates how profoundly the antibiotic-resistance problem can differ between countries and patient populations, we await further information regarding the susceptibility testing results for this current UK outbreak.”

Dr Aidan Taylor, microbiologist at the University of Reading, said: 

“While Salmonella infections occur every year in the UK, outbreaks linked to a single food source that result in hundreds of illnesses and a reported death are relatively unusual and are understandably a cause for concern. The government’s decision to issue a food safety alert reflects the importance of identifying and removing contaminated products from the food chain as quickly as possible.

“Salmonella are bacteria that can cause diarrhoea, fever and stomach cramps, usually within a few days of eating contaminated food. It lives harmlessly in the digestive tract of birds, which is why eggs and poultry are among the foods most commonly associated with infection.

“The good news is that there are straightforward ways people can protect themselves. Cooking eggs and other foods thoroughly, washing hands after handling raw ingredients, avoiding cross-contamination between raw and ready-to-eat foods, and following any official food recall advice can all help reduce the risk.

“If infected, most healthy adults recover without significant treatment, but young children, older people and those with weakened immune systems can be more vulnerable to serious illness.”

Dr Matthew Gilmour, Chief Scientific Officer at the Quadram Institute and Director of the Food Safety Research Network, said:

“An important part of this investigation that isn’t immediately obvious from the headlines is the role of Whole-Genome Sequencing (WGS). UKHSA has used genomics routinely for Salmonella surveillance and outbreak investigation for more than a decade. Whole-genome sequencing reads essentially the entire DNA sequence of the Salmonella bacterium – around five million DNA letters – allowing extraordinarily detailed comparisons between bacteria recovered from different patients.

In this outbreak, all 207 cases belong to the same very closely related genomic group, with only a handful of differences across those roughly five million DNA letters. This provides strong evidence that the infections are part of the same outbreak and indicates a common source.

Genomics has also shown that this strain is related to a Salmonella Enteritidis outbreak investigated in 2025. This is where genomics is particularly powerful: it can reveal connections between cases separated by geography and many months that would be extremely difficult to recognise from case numbers alone. 

Genomics is powerful evidence, but it does not by itself tell us which food made people ill. That comes from combining the genomic evidence with patient interviews, epidemiological analysis and food-chain investigation. UKHSA has interviewed 114 people in the current outbreak and reports that egg consumption is presently the strongest food signal; investigators are then using information about where people ate and where those businesses obtained their ingredients to follow that signal through the supply chain.

Put simply, genomics helps tell us which cases belong together and how they relate to previous outbreaks; epidemiology and food-chain investigation help tell us what those people had in common and where contamination may have occurred. Bringing those different forms of evidence together gives public health teams a much stronger basis for action to protect consumers.”

Prof Brendan W. Wren, FRSB, Co-Director of LSHTM Vaccine Centre, London School of Hygiene & Tropical Medicine, said:

“Salmonella enteritidis causes severe diarrhoea and can be fatal in the elderly or immunocompromised individuals. It is readily transmitted through the handling or consumption of food. Using DNA fingerprinting the outbreak of at 200 cases appears to be from a single source. Through questionnaires’ the most likely source is from the consumption of eggs or egg related products such as mayonnaise. The outbreak control team at the UKHSA are actively investigating the source and routes of transmission of the outbreak.”

Dr Charlotte Hammer, Assistant Professor in Health Security and Infectious Diseases at the Centre for the Study of Existential Risk at the University of Cambridge, said:

“Salmonella Enteritidis is a classic food-borne bacterial pathogen often associated with eggs and poultry. Vaccination of commercial laying hens against Salmonella Enteritidis and Salmonella Typhimurium has been a major public health success in the UK and has substantially reduced egg-associated salmonellosis.

Salmonella Enteritidis is primarily transmitted through contaminated food or water, although infection can also occur through contact with infected animals. Symptoms typically include diarrhoea, abdominal cramps and fever. While most infections are self-limiting, severe disease can occur in young children, older adults and immunocompromised individuals.

Salmonella infections are generally more common during the warmer months of the year, reflecting a combination of biological and behavioural factors that favour transmission. The current outbreak is notable because more than 200 confirmed cases have been linked to a single strain through whole genome sequencing, suggesting a common source of contamination. 

The outbreak highlights the role of modern surveillance systems in food-borne disease investigations. Whole genome sequencing enabled investigators to identify a cluster of cases, link them to a common strain, and assess potential connections with previous outbreaks while supporting coordinated investigations across public health, food safety and animal health agencies. This is the backbone of extensive epidemiological, food-chain, and genomic investigations at the core of such an outbreak. The aim now is to identify the source of contamination and implement measures to control the outbreak.”

Dr Safi Rehman, Research Associate, King’s College London, said:

“Outbreaks like this typically occur when a contaminated food source reaches many people through the supply chain before it’s identified. In this case, health officials traced the strongest link back to eggs imported from outside the UK, consumed in food eaten away from home. The strain responsible, Salmonella Enteritidis, is the most common cause of Salmonella infection in England, and one of the most common worldwide. This isn’t an isolated incident: this outbreak is closely related to one from 2025 that was also linked to imported eggs, with the identified strain genetically similar between the two years.

“UKHSA, working with the Food Standards Agency and other agencies, has been investigating since May 2026: using genetic sequencing to confirm cases are linked, interviewing affected people to trace shared food sources, and identifying specific food premises where advice on food safety has now been given. The investigation remains ongoing.

“Most Salmonella infections occur due to consuming or handling contaminated foods. Symptoms include diarrhoea, stomach cramps, and sometimes vomiting or fever, usually appearing one to three days after exposure. For most people the illness is self-limiting and clears up without treatment, even without seeing a doctor, making a full recovery with no lasting impacts. In a minority of cases, particularly among young children, older adults, and people with weakened immune systems, the infection can spread from the gut into the bloodstream and become significantly more serious. That’s what happened in two of the 207 confirmed cases in this outbreak. As with any bloodstream infection, early recognition and treatment substantially improves outcomes, so anyone with severe or persistent symptoms, or who is in a higher-risk group, should seek medical advice via their GP or NHS 111.”

Dr Kathleen O’Reilly, Associate Professor, London School of Hygiene and Tropical Medicine, said:

“The UKHSA released on Tuesday (18^th Aug 2026) an early report of an outbreak of Salmonella in the UK. Salmonella is a bacterial infection that can cause diarrhoeal disease, and especially in the vulnerable can lead to more severe symptoms. I read with great sadness that in this outbreak a person has died. 

The investigation teams at UKHSA noticed an increased number of cases with the same type of Salmonella – this often indicates an outbreak. The response initially includes looking for more cases and ensuring that cases of diarrhoeal disease have samples so microbiologists that carry out analysis. Teams will investigate using cases to identify possible common sources of infection. From this work, it appears that eating eggs outside of the home, possibly from eggs produced internationally could be a common source. However, at this stage this information is not ‘definitive’ and as the outbreak progresses it is possible other sources may be identified. Investigations will continue to establish likely sources and remove from the food chain. Salmonella infection is common in many animals, including livestock such as chickens and pigs. Considerable efforts are in place to limit infection in animals and reduce the risk to humans.

Previous research has estimated that less than 10% of Salmonella cases require hospitalisation, so it seems initially concerning that 38% in this outbreak have been admitted to hospital. As the epidemic progresses, this number might change, especially as Salmonella cases are often underreported. 

Making sure that eggs are fully cooked before being eaten is best, as always. Hygiene while preparing food is important, especially washing hands with soap and chopping boards after preparation. All catering outlets have a food hygiene rating, so looking at these while deciding where to eat would be wise. If an omelette is still runny, cook it for longer to kill off any bacteria if they are present. If you do get ill with diarrhoea or stomach cramps, take it easy, drink plenty of fluids, and cases will often resolve after a few days. If the illness is in young children, elderly, or other vulnerable groups, it would be sensible to contact your GP or ring 111 to talk with a health specialist.”

Jacquelyn McCormick, Head of Incidents at the FSA, said: 

“We are working closely with the UK Health Security Agency and other partners to investigate an outbreak of Salmonella Enteritidis. The exact cause has not yet been identified, however investigations so far have identified links to eggs imported from outside the UK, mainly used by food service and catering establishments such as restaurants or cafes, as a potential source.  There is no evidence that UK-produced eggs are affected. 

While investigations continue, our advice around eating eggs remains the same. Eggs which are thoroughly cooked and handled hygienically should not present a food safety risk.

Infants, young children, pregnant people and older adults should only eat runny or raw eggs if they have a British Lion mark or are produced under the Laid in Britain egg assurance scheme. This advice does not apply to those who are severely immunocompromised and require medically supervised diets.

We continue to advise people who are handling eggs, eggshells or egg packaging to always wash their hands thoroughly with warm water and soap and dry them properly afterwards.”

Dr Damien Tully, Associate Professor at the Medical Research Council/Uganda Virus Research Institute and London School of Hygiene & Tropical Medicine Uganda Research Unit, said:

“This is a sizeable outbreak, but the number of confirmed cases is likely to be just the tip of the iceberg. Many Salmonella infections cause relatively short-lived gastrointestinal illness and people may recover without ever being tested, meaning the true number of infections associated with an outbreak can be considerably higher than the number identified through laboratory surveillance.

“One of the striking features of this outbreak is that genomic sequencing has allowed more than 200 cases across the UK to be connected. These are people who may have no obvious connection to one another, but the bacteria causing their infections are genetically very closely related. This provides investigators with an important clue that they may be looking at a common source and helps focus the search for where the infections are coming from.

“The genetic relationship with a previous outbreak associated with imported eggs is particularly interesting and gives investigators an important lead. However, establishing the source will require the genomic evidence to be combined with information from cases about what and where they ate, alongside tracing products back through the food supply chain.

“Reassuringly, the outbreak has been identified and is being actively investigated by a number of public health agencies. For most healthy people, Salmonella causes an unpleasant but self-limiting illness, although it can occasionally cause serious disease, particularly in young children, older adults and people with weakened immune systems. Good food hygiene remains important: wash your hands before preparing or eating food, avoid cross-contamination in the kitchen, and make sure foods such as eggs, poultry and meat are cooked thoroughly.”

Declared interests

Prof Owen Spiller: “Professor Owen Spiller is employed by Cardiff University as Professor and Head of Medical Microbiology. He holds honorary contracts as a Consulting Microbiologist with the UK Health Security Agency and Cwm Taf Morgannwg University Health Board, and an adjunct academic appointment at the University of Western Australia.

He is a named international academic collaborator on the Spanish Government-funded RESISTECA project at the University of Zaragoza (“Integrative database for the analysis of antibacterial resistance throughout the food chain”). The funding is held by the University of Zaragoza. His role is to provide academic advice on the design and interpretation of horizontal gene-transfer experiments and on the genomic and phenotypic antimicrobial-susceptibility analyses.

Professor Spiller was a co-author of the 2026 Microbial Genomics study “Salmonella bloodstream infection and concurrent intestinal colonisation in children with severe acute malnutrition in Niger” (DOI: 10.1099/mgen.0.001788). The study was conducted at an inpatient nutritional rehabilitation centre in Maradi, Niger, supported by Médecins Sans Frontières, and was funded by Médecins Sans Frontières Operational Centre Paris.

Current or recent institutional research funding to Cardiff University for projects on which Professor Spiller has been a principal or co-investigator has included funding from the Office for Life Sciences, UKHSA, Health and Care Research Wales, the INEOS Oxford Institute, Gilead, Allied Microbiology International, the Wellcome Trust, the European Society of Clinical Microbiology and Infectious Diseases, the Microbiology Society and the Society for Applied Microbiology.

Industry-linked or commercially derived institutional funding includes approximately £1.40 million from the INEOS Oxford Institute across three AMR projects during 2022–2026, a £48,000 Gilead-funded public-engagement project during 2023–2024, and a £3,000 Allied Microbiology International studentship in 2024. These were institutional research awards rather than personal consultancy payments.

Professor Spiller is also a co-inventor and co-holder of the patented LASARUS culture medium for Legionella; this has no connection to Salmonella, eggs, poultry production or the present outbreak.”

Dr Aidan Taylor: “Has not reported any conflicts on this. He has previously received an AMS grant to study food poisoning bacteria.”

Dr Matthew Gilmour: “Dr Gilmour is Director of the Food Safety Research Network, which has received funding from the FSA and BBSRC.”

Prof Brendan Wren: “I have no conflicts of interest from making my statement.”

Dr Charlotte Hammer: “No conflicts to declare.”

Dr Safi Rehman: “No conflicts of interest.”

Dr Kathleen O’Reilly: “Received funding from the National Institute for Health Research for research into climate change and the effects on infectious diseases in the UK. Received funding from the World Health Organisation for research and committee membership for polio eradication. Received funding from the Gates Foundation for research on polio eradication. I have not received any funding from industry”

Jacquelyn McCormick: “There are no DOIs to declare”

Dr Damien Tully: “No COIs to declare.”