How Salmonella from eggs can cause deadly infections amid UK outbreak

For most people, a Salmonella infection causes gastroenteritis, an inflammation of the stomach and intestines that can mean several miserable days of diarrhoea, cramps, fever or vomiting. Most people recover within a week. But severe diarrhoea and dehydration can still be dangerous, even while the bacteria remain confined to the gut.

In a small minority of patients, however, Salmonella crosses the gut lining and enters the blood. In the current UK outbreak , seemingly caused by eggs imported from abroad, two people have developed bloodstream infections and one death has been associated with the outbreak . How does a familiar cause of food poisoning escape the gut, and why does this only happen to some people?

By August 13 2026, the UK Health Security Agency had identified 207 confirmed cases of a closely related strain of Salmonella Enteritidis. Among patients for whom the relevant information was available, 38% had been admitted to hospital because of their symptoms.

Egg consumption is investigators’ strongest lead, although the source remains unconfirmed. Several affected people ate egg dishes at food businesses supplied by several sources, including importers. Investigators also identified possible opportunities for cross-contamination, in which bacteria are transferred between foods or surfaces, at two premises. They have found no link to UK-produced eggs or poultry.

Salmonella Enteritidis belongs to a broad group called non-typhoidal Salmonella, which is distinct from the bacteria that cause typhoid and paratyphoid fever. Doctors describe an infection as invasive when Salmonella reaches the blood or another part of the body that is normally free of bacteria. A bloodstream infection can lead to sepsis, a life-threatening reaction in which the immune system begins damaging the body’s organs and tissues.

Genes, which are sections of DNA containing biological instructions, allow Salmonella to build tiny injection systems that work like molecular syringes. One injects proteins into cells lining the gut, causing them to engulf the bacterium. These injection systems are found in many Salmonella bacteria , so their presence cannot explain why one patient develops a bloodstream infection while another has relatively mild diarrhoea. In most people, several layers of immune defence contain the infection in the gut.

A second helps Salmonella alter the membrane-wrapped compartment that forms around it after an immune cell swallows it, allowing some bacteria to survive and multiply. Macrophages are immune cells that engulf and usually destroy microbes. Some Salmonella can survive inside them. This sheltered position is one way the bacteria may move into deeper tissues and the bloodstream, although other routes may contribute.

Scientists have identified more than 2,600 types of Salmonella, known as serovars, although fewer than 100 cause most human illness. A strain is a more closely related genetic branch within one of these types.