The Centers for Disease Control and Prevention in Atlanta said there are three other probable cases of STEC O121 infections linked to the same sprouts.
Preliminary trace back investigations indicate contaminated raw clover sprouts produced by Evergreen Fresh Sprouts, LLC, of Idaho is the likely source of this outbreak of STEC O121 infections, but the investigation is ongoing.
In state and local interviews of the patients, health officials found 9 of 10 reported eating raw clover sprouts in the week before becoming ill.
The Washington state Department of Health and the Idaho Department of Health advise people not to eat raw clover sprouts produced by Evergreen Fresh Sprouts.
The CDC said 50 percent of those sickened were hospitalized, but none of the patients developed hemolytic uremic syndrome -- a type of kidney failure. No deaths were reported.
Shiga toxin-producing E. coli, or STEC, frequently causes severe disease, including bloody diarrhea and hemolytic uremic syndrome. STEC bacteria are divided into serogroups O157 or O121.
E. coli O157 is the STEC serogroup found most commonly in U.S. patients, but other E. coli serogroups in the STEC group, including O121, are sometimes called "non-O157 STECs."