In April 2018 local, state and federal public health and agriculture agencies announced an outbreak of E. coli O157:H7 and E. coli O61 infections linked to romaine lettuce from the Yuma, Arizona growing region. On June 28, 2018 the CDC declared the outbreak over.

A total of 240 people were diagnosed with Shiga Toxin E. coli. One hundred four people were hospitalized including 28 people who developed Hemolytic Uremic Syndrome (HUS). Five people died. Cases were reported from 36 states. Illness onset dates ranged from March 13, 2018 to June 6, 2018. WGS analysis of isolates from 184 ill people identified antibiotic resistance to chloramphenicol, streptomycin, sulfisoxazole, tetracycline, and trimethoprim-sulfamethoxazole. These findings did not affect treatment guidance since antibiotics are not recommended for patients with E. coli O157 infections.

Epidemiologic, laboratory and traceback evidence linked the outbreak to consumption of romaine lettuce from the Yuma growing region. The FDA and state and local regulatory officials traced the lettuce to many farms in the Yuma growing region. CDC laboratory testing identified the outbreak strain of E. coli O157:H7 in water samples taken from a canal in the Yuma region. Whole genome sequencing showed that the E. coli O157:H7 found in canal water was closely related genetically to the E. coli O157:H7 found in ill people.

The Public Health Agency of Canada identified 8 people in several Canadian provinces infected with the same DNA fingerprint of E. coli O157:H7. Canadian illnesses were reported by 5 provinces: British Columbia, Alberta, Saskatchewan, Quebec, and Ontario. One of the Canadian cases were hospitalized and no deaths were reported.