Tomatoes carrying a rare form of salmonella have sickened more than 800 people, and federal officials warn that they may still be on the market, two weeks after the risk was first revealed.

Investigators are considering the possibility that other produce may be spreading the bacteria as well.

According to the FDA, it is safe to eat all cherry tomatoes, grape tomatoes and tomatoes attached to the vine. Roma, red plum and red round tomatoes not attached to a vine are safe if they were grown in certain areas.

After tomatoes are picked, they are often repacked to meet the customer specifications. In the process, tomatoes from many farms are combined, making it harder to trace a shipment back to where it was grown.