One person has died and more than 120 others including children as young as six have been hospitalised in the UK amid an E coli outbreak linked to lettuce.

Two people in England died within 28 days of infection with shiga toxin-producing E coli (Stec), the UK Health Security Agency (UKHSA) said in a briefing on Thursday.

“Based on the information available from health service clinicians, one of these deaths is likely linked to their Stec infection,” the agency said. “Both individuals had underlying medical conditions. The deaths occurred in May.”

As of 25 June, there have been a further 19 cases of Stec, bringing the total number of confirmed cases to 275 in the UK, according to the briefing on the UKHSA website.

There have been 182 cases in England, 58 in Scotland, 31 in Wales and four in Northern Ireland. All those affected had symptoms before 4 June.

Several food manufacturers have recalled sandwiches, wraps and salads sold in big supermarkets and retail chains over fears they are linked to the outbreak. The Food Standards Agency (FSA) has previously said lettuce used in the products is thought to be the likely source of the outbreak.

Based on data from 249 cases, 49% of those affected were hospitalised, the UKHSA said. It means at least 122 people have been admitted to hospital for treatment since the start of the outbreak. The Guardian understands that children as young as six and adults as old as 85 were among those hospitalised.

The victims include an 11-year-old girl from the north-west who became seriously ill and was hospitalised after eating a supermarket own-brand chicken salad sandwich.

She was on dialysis for almost three weeks after developing haemolytic uraemic syndrome (HUS), a clinical syndrome associated with Stec that can lead to kidney failure and death.

“Thankfully, she is now stable enough to return home, but HUS is a very serious condition that can cause permanent damage to the kidneys which can affect people for life,” said Claire Glasgow, of the legal firm Fieldfisher, which is representing the girl’s family.

E coli is a diverse group of bacteria that are normally harmless and live in the intestines of humans and animals. However, some strains produce toxins that can make people very ill, such as Stec.

People infected with Stec can have diarrhoea, and about 50% of cases have bloody diarrhoea. Other symptoms include stomach cramps and fever. Symptoms can last up to two weeks in uncomplicated cases.

Some patients, mainly children, may develop haemolytic uraemic syndrome, which is a serious life-threatening condition resulting in kidney failure. A small proportion of adults may develop a similar condition called thrombotic thrombocytopenic purpura (TTP).

Stec is often transmitted by eating contaminated food but can also be spread by close contact with an infected person, as well as direct contact with an infected animal or where it lives.

The UKHSA incident director, Amy Douglas, said she expected to see more cases linked to the outbreak as further samples were referred to the agency for testing.

Darren Whitby, the head of incidents at the FSA, said: “Earlier this month, we confirmed that several sandwich manufacturers had taken precautionary action to withdraw and recall various sandwiches, wraps, subs and rolls after food chain and epidemiological links enabled us to narrow down a wide range of foods to a type of lettuce used in sandwich products as the likely cause of the outbreak.

“This remains a complex investigation and we continue to work with the relevant businesses and the local authorities to ensure necessary steps are being taken to protect consumers.

“Although we are confident in the likely source of the outbreak being linked to lettuce, work continues to confirm this and identify the root cause of the outbreak with the growers, suppliers and manufacturers so that actions can be taken to prevent a reoccurrence.”

Dr Aidan Taylor, a lecturer in microbiology at the University of Reading, said the outbreak was “a serious public health concern”.

He said: “This outbreak highlights the importance of robust food safety measures throughout the supply chain and highlights the need for continued vigilance in both industry practices and consumer awareness.”