Over the past week, another 23 people were sickened by romaine lettuce tainted with E. coli, bringing the total to 121 people in 25 states, the U.S. Centers for Disease Control and Prevention said Wednesday.

The CDC continues to warn consumers not to buy or eat romaine lettuce in any form — whole head, chopped, or in salad mixes — unless they are sure it did not come from the Yuma, Ariz. growing region.

Federal investigators have identified one Yuma area farm as the source of whole-head romaine that sickened several people at a jail in Alaska, but officials still don't know whether the contamination occurred on the farm or later in the supply chain. Most illnesses in this outbreak are not linked to that farm, and dozens of other fields are still being tested.

>>READ MORE: Why E. coli keeps getting into our lettuce

The current outbreak, which began in mid-March, is caused by a particularly virulent strain of E. coli, a bacteria than normally lives in the intestines of people and animals. Half of the 102 people who got sick wound up in the hospital with severe diarrhea, vomiting, and in 14 cases, kidney failure. One death has been reported from California, which has the most cases — 24. Pennsylvania is next with 20 cases.

Although the Yuma growing season and lettuce shipments have ended, the CDC expects the case count to continue to grow because of the lag time in the state reporting process.