Between September 16, 2008, and October 4, 2008, Boulder County Public Health (BCPH) received a total of 19 confirmed and suspect cases of Shiga toxin producing E. coli (STEC) O157:NM. Of those cases, 14 were lab confirmed to have matching PFGE patterns, and the pattern was unlike any other reported outbreak.
Because most of the cases in this outbreak became ill at a Boulder Jimmy John’s Restaurant, Boulder County Public Health lead the investigation into the outbreak. Ultimately, in addition to the 19 confirmed Boulder County cases, one case was identified in each of the following counties: Arapahoe, Broomfield, Jefferson and Weld. BCPH reported: “Of the cases not in Boulder County, 2 of 4 (50%) reported eating food from a Jimmy John’s restaurant—one at the sorority house and one at a Jimmy John’s restaurant located in Adams County, Colorado. All 17 cases (100%) in Boulder County reported eating food from Jimmy John’s restaurant located in Boulder.”
Because residents of different counties who had eaten at different restaurants were falling ill at roughly the same time due to infection by the same strain of E. coli O157, investigators focused on potentially contaminated ingredients distributed to all the restaurants where outbreak cases had recently eaten. Suspects initially included lettuce, tomatoes, and sprouts; ultimately, however, based on BCPH’s in depth investigation, alfalfa sprouts were identified as the outbreak vehicle.
Based on their detailed traceback investigation, investigators ultimately found that one company, Sprouts Extraordinaire, had supplied alfalfa sprouts to not only the Boulder Jimmy John’s, but also the Federal Height’s (Adams County) Jimmy John’s where Nichola Battista was exposed, as well as the Pita Pit in Greeley, Colorado, where another PFGE matched case had consumed sprouts two days before onset of illness.
CDPHE and FDA both participated in the investigation at Sprouts Extraordinaire. Unsurprisingly considering the nature of the product, none of the samples from the implicated lot tested positive for the outbreak strain of E. coli O157. Nonetheless, by the date of the inspection at Sprouts Extraordinaire, there was “increas[ing] epidemiological certainty by the Epi Division at CDPHE that the alfalfa sprouts and seeds originating at Sprouts Extraordinaire were strongly associated with 14 confirmed E. coli illnesses associated with sprout consumption at the Boulder Jimmy Johns restaurant and other possible locations.”
In conclusion to its outbreak report, BCPH states as follows:
This analysis indicates that while the outbreak is likely due to a common source, the exposures may have occurred at different times. The matching PFGE patterns of all the confirmed cases indicate that a common source is responsible for each of the E. coli infections. Despite inconclusive laboratory evidence to indicate that the alfalfa sprouts was the source of the E. coli illnesses, there is signficiant epidemiologic evidence to indicate that both alfalfa sprouts and secondary person-to-food transmission at Jimmy John’s in Boulder contributed to the spread of illness.
BCPH’s investigation revealed alfalfa sprouts as the common source of E.coli infection among the cases. The alfalfa sprouts served at the three restaurants were traced back to a single supplier. On October 10th, an inspection of Sprouts Extraordinare was conducted by Colorado Department of Public Health and Environment, Consumer Protection Division Food Program managers. Multiple deficiencies were identified during the inspection including food contact equipment not properly sanitized and the lack of handwashing sinks in the production room. Sprout, sprout seed, water, and food contact surfaces sampled during the inspection were negative for bacterial pathogens. Even though E. coli was not found during visit to the sprout supplier/grower, does not rule-out sprouts as the source of infection for this outbreak. Seed contamination can be sporadic and samples were collected after the outbreak period.
Based on the BCPH epidemiologic cohort study, the single unique PFGE pattern found among all culture-confirmed cases, reports of cases eating sprouts from more than one location with the same sprout supplier, alfalfa sprouts were more likely than not the source of E. coli for this outbreak and the source of infection/contamination for the Boulder County Jimmy John’s.