Fifteen people are believed to have suffered from Salmonella after eating in a Cumbrian town, officials have said.
Ten cases of the bug have been confirmed by laboratory tests and there are five probable cases awaiting confirmation.
Officials say all those taken ill had visited Penrith over the weekend of 15-16 November.
However, they are unable so far to pinpoint the source of the illness, said a statement.
Specialists from the Cumbria and Lancashire Public Health England Centre and environmental health officers from Eden District Council are investigating.