Investigators searched nine California farms for evidence of spinach-borne E. coli yesterday, going into the fields for the first time, as the number of confirmed illnesses rose by 17 to 131.

A team of about a dozen investigators from the Food and Drug Administration and the state of California fanned out to farms in Monterey County’s Salinas Valley, according to Kevin Reilly, deputy director of the California Department of Health Services. The farms grew spinach for Natural Selection Foods LLC and River Ranch Fresh Foods LLC, which have recalled all of their fresh spinach.

Federal officials focused on those nine farms after records provided by Natural Selection and River Ranch indicated a link to bags of spinach eaten by those who became ill, reports the Washington Post.

The outbreak appears particularly virulent, though that could change as more cases are reported. Of the 131 cases, 66 people have been hospitalized, 20 have experienced kidney failure, and one person has died — a higher than expected proportion.

Some victims have retained lawyers for possible lawsuits. William Marler, a Seattle lawyer who specializes in food poisoning cases, said he is representing 30 victims of the outbreak, 11 of whom have developed kidney failure as a result of hemolytic uremic syndrome.