Health authorities in the United States are investigating a multistate E. coli outbreak linked to frozen blueberries after 12 people fell ill, including four who required hospitalisation. The outbreak has prompted a nationwide recall of a popular brand of frozen organic blueberries sold through Publix supermarkets.

According to the U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA), all reported cases involve the E. coli O145 strain. As of July 6, eleven infections have been reported in Florida and one in Georgia.

Although illnesses have so far been confirmed in only two states, the recalled frozen blueberries were distributed to Publix stores across eight states, including Alabama, Florida, Georgia, Kentucky, North Carolina, South Carolina, Tennessee and Virginia. Health officials have urged consumers in these states to check their freezers and avoid consuming the recalled product.

The affected individuals developed symptoms between May 11 and June 5. Patients range in age from two to 88 years. Four people have been hospitalised, but no deaths have been reported.

Investigators traced the outbreak to frozen blueberries after interviewing patients about foods they had recently consumed. Of the nine people questioned, seven reported eating frozen blueberries before becoming ill, a much higher proportion than the 24% reported in a national food consumption survey.

Laboratory analysis further strengthened the link. DNA fingerprinting showed that the bacteria isolated from infected patients were genetically very similar, indicating they likely originated from the same contaminated food source.

Following the investigation, Frutas y Hortalizas del Sur S.A., a company based in San Carlos, Chile, recalled GreenWise Organic IQF Blueberries sold in 10-ounce bags with lot code 60401 and a best-before date of February 9, 2028. Publix has also removed the product from all its stores.

E. coli infection typically causes severe stomach cramps, diarrhoea, often with blood, and vomiting, with symptoms usually appearing three to four days after consuming contaminated food. While most people recover within five to seven days, some develop a serious kidney complication known as hemolytic uremic syndrome (HUS), which may require hospital treatment.

Health officials have advised consumers who have purchased the recalled blueberries to throw them away or return them to the store for a refund. They also recommend thoroughly washing any containers, utensils or surfaces that may have come into contact with the contaminated fruit using hot, soapy water.

People are urged to seek immediate medical attention if they develop warning signs such as a fever above 102°F, bloody diarrhoea, diarrhoea lasting more than three days, persistent vomiting that prevents fluid intake, or symptoms of dehydration.

The CDC cautioned that the actual number of infections is likely higher than currently reported because many people recover without undergoing laboratory testing, while some recent cases may not yet have been recorded.