Snohomish County Health District (SCHD) Communicable Disease (CD) program received the first report of a confirmed E. coli O157:H7 illness, in what would soon become a cluster of such illnesses, on October 14, 2008. The next report of illness came the following day, October 15. It was subsequently determined that both ill individuals had dined at Ixtapa in Lake Stevens in the days before onset of their illnesses.
The third and fourth reports of illness came in on October 16, and when these people reported that they, too, had eaten at Ixtapa, SCHD knew that an outbreak was underway. Many more reports of illness followed. Accordingly, SCHD issued a press release on October 21, 2008, stating that the health authorities investigating the cluster of E. coli O157:H7 illnesses had “narrowed down the likely source of E. coli illness . . . [to] Ixtapa restaurant, 303-91st Ave. NE. #B201.” Ixtapa voluntarily closed for business the same day so that it could be sanitized.
After identifying Ixtapa as the source, investigators were able to focus their inquiry to try to determine whether a particular food item, or a contaminated food-handler, was the ultimate outbreak vehicle. The Communicable Disease program accomplished this by statistical analysis of food items generated during a case-control study, and an environmental investigation at the restaurant itself. After performing these in-depth analyses, “guacamole remained the only significant food exposure identified.” But other vehicles by which bacteria may have infected Ixtapa customers could not be ruled out, including the salsa, cross-contamination from a contaminated ingredient, or contamination by an infected foodworker (possibly asymptomatic).
Ultimately, investigating health officials counted twenty-three “confirmed” and “probable cases,” and forty-one “suspect cases.” The average incubation period for the twenty-three confirmed and probable cases was about four and one-half days, with a range of one to eight days. Four confirmed cases were hospitalized, and one developed hemolytic uremic syndrome. Finally, testing at the WSDOH Public Health Lab showed that the PFGE pattern associated with the outbreak was EXHX01.2134 (Xbal) and EXHA26.0888 (Bln). WSDOH designated this outbreak 2008-0444.