The report released Monday by Alberta Health Services says it's not possible to say if the bacteria came from a contaminated ingredient in the meat loaf or into the meat loaf from elsewhere on the menu or through an infected kitchen worker.

The E. coli outbreak, declared on Sept. 4, 2023, led to at least 448 infections.

There were 38 children and one adult hospitalized for severe illness.

Of the severe cases, 23 were diagnosed with hemolytic uremic syndrome, a condition that damages blood vessels and kidneys and can lead to life-threatening kidney failure.

Eight received peritoneal dialysis, which is done to remove waste products from the blood when the kidneys are failing.

Another 33 secondary cases have also been linked, including household contacts and children in other daycare facilities.

There were no deaths.

The outbreak was linked to Shiga toxin-producing Escherichia coli, or STEC for short.

"This is the largest gastrointestinal outbreak in AHS history and likely one of the largest STEC outbreaks involving child-care facilities anywhere," said the report.

"The central kitchen served up to 1,275 attendees and 250 child-care facility workers during the period in question, in addition to exposures to kitchen staff and people in the community who ate leftovers."

The eight-week outbreak was traced back to Fueling Minds, a catering company and school lunch delivery service provider that prepared food for its Fueling Brains locations and other daycares in Calgary.

The report narrowed the E. coli down to a single meal served from the Fueling Minds central kitchen on Aug. 29, 2023.

"One meal originating from the central kitchen came out with extremely high odds as being the source of inspection. The beef meat loaf served at lunch on Aug. 29, 2023, was the probable food item containing the E. coli," said the report.

"Workers who ate beef meat loaf were 23 times more likely to become a confirmed STEC case than workers who did not eat beef meat loaf."

E. coli is a type of bacteria that can cause bloody diarrhea. Some strains cause more severe illness. Shiga toxin-producing E. coli is different as it produces a toxin that can cause complications.

In response to the outbreak, the province launched a third-party review to determine how to prevent similar outbreaks in the future.

That report, by the Food Safety and Licensed Facility-Based Child Care Review Panel and also released Monday, made 12 main recommendations to protect the health and safety of children in licensed child-care facilities.

The Alberta government said it has already started work on implementing some of the changes, including increasing the frequency of inspections at child-care facilities, mandatory training programs for food workers and improving response times in child-care facilities where food safety concerns have been raised.

Planning is also underway to require all licensed child-care providers to prominently post their most recent public health inspection reports for parents to review.

"It's our government's intention to act on every recommendation we can to protect children's safety and to restore trust in the system," Premier Danielle Smith said in a statement.

"Last year's E. coli outbreak had a devastating impact on families, and we are committed to making sure an event like that never happens in our province again."

The Fueling Minds kitchen was closed after the outbreak and reopened in November under a different food provider.

Fueling Minds and its directors has been charged by the City of Calgary with serving food to the child-care centres without a licence.

They have pleaded not guilty and face fines up to $120,000, and a trial is set for September.

This report by The Canadian Press was first published July 29, 2024.