LONDON — One person died from an E. coli outbreak that sickened at least 275 people in the United Kingdom during the past month, health officials said Thursday.

The outbreak that led to 122 people being hospitalized was linked to lettuce in pre-packaged sandwiches, the U.K. Health Security Agency said.

Two patients with Shiga toxin-producing E. coli died in May but only one of the deaths was likely linked to the infection, the agency said. Both of the people who died had underlying medical conditions.

E. coli bacteria normally live in the intestines of healthy people and animals, according to the Mayo Clinic. While most strains are harmless and cause relatively brief diarrhea, some strains can cause a range of conditions, including urinary tract infection, cystitis, intestinal infection and vomiting, with the worst cases leading to life-threatening blood poisoning.

More than 80% of the people sickened in the latest outbreak had bloody diarrhea, the UKHSA said.

Companies that make sandwiches sold by major grocery stores and retail chains throughout the U.K. issued voluntary recalls of sandwiches, wraps and salads beginning June 14.

New cases have declined recently.

The investigation into the source of the outbreak is ongoing.