An E. coli outbreak in Huntsville, Alabama, that has sickened numerous customers of Little Rosie’s and has sent at least three people to the hospital with hemolytic uremic syndrome, was caused by contaminated lettuce, according to the Madison County Health Department. The Huntsville Times reports that health officials have not determined when the lettuce became contaminated – if it was before or after it entered the restaurant, but they are looking into the possibility that the lettuce was cross-contaminated before it was served.

Five-year-old Samuel Coggin of Meridianville started dialysis Wednesday morning at Vanderbilt Children’s Hospital in Nashville. Two adults whose names have not been released are also hospitalized with kidney problems: a 48-year-old woman in critical condition at Huntsville Hospital and a 70-year-old woman undergoing dialysis in Asheville, N.C.

Dr. Debra Williams, the Huntsville-Madison County Health Department’s assistant director, said 16 people who ate at Little Rosie’s Taqueria late last month have now tested positive for E. coli O157:H7 poisoning. A 17th E. coli victim did not eat at the Whitesburg Drive restaurant and was sickened by a different source, she said.

Three more restaurant customers who were hospitalized with symptoms of E. coli exposure have tested negative, Williams said.