The E. coli outbreak that has the Centers for Disease Control and Prevention (CDC) urging consumers to avoid romaine lettuce is linked to an unusually high number of hospitalizations, according to an update issued Wednesday.
Thirty-one more cases have been added to an ongoing investigation into the outbreak, bringing the total number of sick individuals across 19 states to 84. About 54% of these patients — 42 out of the 78 with available information — have been hospitalized, according to the CDC. That’s significantly higher than the infection’s typical 30% hospitalization rate, according to the agency.
CDC spokesperson Brittany Behm tells TIME that officials are still trying to determine what’s behind that higher-than-normal hospitalization rate, and whether this particular strain of E. coli is more virulent than other forms of the bacteria.
E. coli infection typically causes gastrointestinal problems that clear within about a week, though some cases can come with complications including a type of kidney failure called hemolytic uremic syndrome. Nine patients, about 10% of the total sample, have reported this complication, compared to about 5% in an average outbreak, Behm says. No deaths have been reported.
CDC officials have traced the outbreak back to romaine lettuce grown in the Yuma, Ariz., region. At first, advisories specifically pertained to chopped romaine lettuce, but the agency later updated its consumer advisory to include whole heads and hearts of romaine.
Consumers, for the time being, have been advised to throw away any store-bought romaine lettuce and to avoid buying more, or ordering it in a restaurant, unless they can confirm it was not sourced from the Yuma area.