An outbreak of salmonella in fresh red onions has sickened 396 people in 34 states and sent 59 to the hospital, according to the Centers for Disease Control.

The outbreak has been traced to onions from Thomson International, a produce supplier based in Bakersfield, Calif. The onions were shipped in bulk to both foodservice and retail customers, under names including Thomson Premium, Tender Loving Care, Hartley’s Best, and store brands for Kroger, Food Lion and other retailers.

Thomson issued a voluntary recall Aug. 1 for red, white and yellow onions distributed after May 1. However, authorities are concerned because bulk-shipped onions are difficult to trace back from the consumer. Authorities are looking at contaminated irrigation water as a possible source for the outbreak.

Lawsuits have been filed in connection with the incident, on behalf of consumers who were sick for more than a week.