Romaine lettuce tainted with E. coli has sickened 84 people in 19 states, including 18 in Pennsylvania, which continues to have the most cases, according to an update issued Wednesday by the U.S. Centers for Disease Control and Prevention.

Thirty-one new cases have been identified since the last count on April 18, the CDC said.

Last week, the agency broadened its warning, saying consumers should not eat or buy romaine in any form — including whole heads, hearts, chopped, or in salad mixes — unless they can confirm it is not from the Yuma, Ariz., growing region. Restaurants and retailers should not serve or sell romaine from that region.

Of those who became ill with severe diarrhea and vomiting, 42 people have been hospitalized, including nine who developed a type of kidney failure. That's a higher hospitalization rate than usual with E. coli, so this is a particularly virulent strain, the CDC said.

Federal and state investigators are still trying to identify the precise source of the contaminated romaine lettuce.