The 172 reported illnesses, which resulted in one death and 75 hospitalizations, have been traced to lettuce harvested in April in the winter lettuce region around Yuma, Ariz., according to the CDC.
Iowa, Nebraska and Oregon newly joined the list of 32 states that have reported illnesses linked to romaine lettuce.
The CDC and Food and Drug Administration have struggled for more than a month to pinpoint a source for the contamination, which became evident in early April. No recall was issued.
One Yuma-area field, Harrison Farms, was identified as the supplier of whole romaine lettuce to prisoners who fell ill at a correctional facility in Nome, Alaska. But authorities are not sure where in the supply chain the contamination might have occurred, and have said they are investigating more than a dozen additional sites.
