The number of cases is rising in the U.S. outbreak of Cyclopora linked to bagged salad, but authorities are yet to discover the source.

As of July 22, the Centers for Disease Control (CDC) is reporting a total of 641 cases across 11 predominantly Midwestern states. No deaths have been reported.

The investigation includes Fresh Express branded products as well as products made by Fresh Express for retail store brands sold at ALDI, Giant Eagle, Hy-Vee, Jewel-Osco, ShopRite, and Walmart.

CDC and Food and Drug Administration (FDA) investigators continue to look into whether other retail brands may be impacted.

FDA’s traceback investigation is ongoing to determine the cause and source of the outbreak.

Salad ingredients (iceberg lettuce, carrots, red cabbage) continue to be items of interest in the investigation.