Feb 26, 2008 (CIDRAP News) – Officials from California and the US Food and Drug Administration (FDA) recently released a final report on a 2006 Escherichia coli O157:H7 outbreak associated with iceberg lettuce from Taco John's restaurants in Iowa and Minnesota, revealing that wastewater from nearby dairy operations might have contaminated irrigation water.
The 41-page FDA/California Department of Public Health report, released on Feb 15, linked the outbreak to a ranch in Buttonwillow, Calif., that is located about 126 miles northwest of Los Angeles.
The outbreak occurred in the fall of 2006 and sickened about 80 people, according to the report. No deaths were reported. E coli O157:H7 produces a toxin that causes diarrhea—often bloody—and abdominal cramps, but typically no fever. The illness usually resolves in 5 to 10 days, but it can cause hemolytic uremic syndrome, potentially leading to kidney failure or death, in 2% to 7% of patients.
Investigators from the Minnesota Department of Agriculture and the Iowa Department of Public Health had identified shredded iceberg lettuce served at the restaurants as the likely cause of the E coli outbreak. The FDA, working with Minnesota and California officials, had traced the lettuce the restaurants received from a Minnesota distributor to growing regions in California's Central Coast and Central Valley areas.
Further trace-back studies by the FDA and California authorities steered investigation and sampling to two growing areas, but investigators focused their efforts on the Wegis Ranch in Buttonwillow after 10 of the 32 samples from the site matched the Taco John's outbreak strain, according to the report.
Four of the samples matching the outbreak strain came from two dairies located near the lettuce fields.
After analyzing water systems in the area and at the ranch, investigators found several confluence points between the local water district's system and those of the ranch and the two dairy operations.
"A key finding in this investigation was the dairy wastewater blending and distribution system used by the Wegis Ranch to irrigate crops and distribute water," the investigators wrote. They also reported that the system had inadequate backflow devices, which might have contaminated the growing fields with wastewater.
The report also said numerous signs of wildlife were observed near and on some of the ranch's growing fields.
Feb 15 FDA/California Department of Public Health final report on E coli O157:H7 outbreak in lettuce
Jan 12, 2007, CIDRAP News story "FDA finds Taco John's E coli strain on California farms"