The Associated Press reports that Danish health officials are checking everything from refrigerators to credit card receipts to find the source of what may be the worst Salmonella outbreak in 15 years.

Kare Moelbak of the Ministry of Health said 330 cases of the relatively rare Salmonella typhimurium U292 have been confirmed and about a quarter of those people have been hospitalized.

Moelbak said he suspects the source is some sort of Danish food product distributed only in Denmark, since neighboring countries have not reported an outbreak. They believe it probably is meat, but they do not know which product.