A jar of Loyd Grossman korma sauce at the centre of a botulism outbreak may have become contaminated after leaving the factory.

An investigation by Scottish health authorities has determined that three children from the same family became ill last November after eating sauce from a jar of the Premier Foods sauce.

The outbreak prompted the recall of a batch of the sauce, but in a report issued on Friday investigators said they found no evidence of failings at the production facility or in the distribution chain that could have led to the contamination. This echoed an announcement made by the Food Standards Agency in the weeks after the outbreak, when the agency said it found no evidence of botulism at Premier’s factory.

Investigators also said the fact that cases were confined to a single household strongly suggested only one jar was contaminated, making a manufacturing fault “very unlikely”.

There was no evidence that the jar was contaminated during the three days it was in the family’s house either, said investigators, adding that if it had been contaminated there, it was unlikely that there would have been time for spores to germinate and produce toxin

“A speculative explanation is that, at some point between manufacture and entering the family’s house, the jar’s seal was broken (either deliberately or accidentally) allowing the ingress of C.botulinum spores,” said the report.