A foodborne illness outbreak linked to raw oysters has sickened at least 25 people who dined at local restaurants recently, King County reported on Tuesday. The news comes after the county reported last week that a handful of people got sick eating raw oysters at two Seattle restaurants – The Salted Sea and The White Swan Public House.

The restaurants, however, are not the source of the outbreak, King County says. Most likely, the oysters were mishandled or contaminated before reaching local restaurants, although no specific local oyster beds have been connected to the outbreak.

County health officials believe diners have been sickened by Vibrio, a marine bacteria commonly found in oysters.

“Eating undercooked or raw shellfish, especially raw oysters in warm-weather months, is the main risk for acquiring vibriosis from infection with Vibrio parahaemolyticus,” King County said.