The Romaine lettuce people are laughing now.

Health officials say ground beef is the likely source of a food poisoning outbreak that has sickened more than 100 people in six states.

The Centers for Disease Control and Prevention on Friday said no specific brand or source of the meat has been determined yet.

The CDC says people can continue to eat ground beef. The meat should be cooked thoroughly to 160 degrees to kill germs.

The outbreak started in early March. So far, 109 people have been infected with E. coli O103, an unusual strain of the bacteria. They reported eating ground beef at home and at restaurants. Seventeen people have been hospitalized. No one has died.