In early August 2015 Public Health Seattle King County (PHSKC) investigated an outbreak of E. coli O157:H7 infections that occurred among 5 customers of the Chipotle Mexican Grill located at 1415 Broadway in Seattle, Washington. Illness onset dates occurred on July 28, 2015 (1 case), July 29 (2 cases) and July 31 (2 cases). All five cases reported experiencing diarrhea that turned bloody and abdominal cramps. Two cases reported vomiting. Two cases reported fever. Three cases were hospitalized. Two sought treatment at an emergency department. None of the patients developed Hemolytic Uremic Syndrome. There were no deaths. The Washington Department of Health (WDOH) Public Health Laboratory (PHL) conducted genetic testing by pulsed field gel electrophoresis (PFGE) on isolates cultured from patients’ specimens. Test results showed that all were infected with an indistinguishable genetic strain assigned PulseNet Identification Numbers EXHX01.0012/EXHA26.1779. This strain had not been seen previously in King County.