SAN FRANCISCO – Like lab technicians on a crime-scene television drama, investigators have tracked a strain of bacteria over thousands of miles — from bagged spinach in Midwestern refrigerators to the guts of a wild pig in the hills of California's central coast.
While they may never pinpoint the exact source of the strain of E. coli blamed for killing three people and sickening more than 200, they have come closer than ever before. And experts say the investigation has yielded valuable clues for preventing future outbreaks.
"We've completely overhauled the way we test and package greens," said Samantha Cabaluna, a spokeswoman for Natural Selection Foods LLC, the company that packaged the tainted spinach. "Regardless of the source or method of contamination, we're better prepared to catch it."
That's little solace to victims and their families.
"This was a long, convoluted story that took a long time to unfold," said Ken Costello, whose elderly mother-in-law was among those who died.
The case started with scattered reports of people falling sick. A 6-year-old boy in Wisconsin had bad cramps. A 12-year-old girl in Kentucky was hospitalized with vomiting. An elderly woman died in Wisconsin.
Health officials began posting DNA profiles of the responsible bacteria to a national database operated by the Centers for Disease Control and Prevention.
A pattern emerged: They were all caused by the same strain of E. coli, short for Escherichia coli, a common and ordinarily harmless intestinal bacteria, and bags of spinach were found in victims' refrigerators.
Suspicion quickly focused on California's Salinas Valley, which grows a large portion of the nation's fresh spinach and had been cited in other E. coli outbreaks linked to salad greens.
The U.S. Food and Drug Administration was alerted on Sept. 13, and within hours it had launched one of the most extensive investigations in its history.
"We put more people and far more resources into this than ever before," said Jack Guzewich, director of emergency coordination and response for the FDA's Center for Food Safety and Applied Nutrition.
By Sept. 14, the bacteria, identified as the O157:H7 strain of E. coli, had been blamed for 49 illnesses and one death.
More than two dozen "food detectives" fanned out in the quest to determine where the contamination had occurred along the greens' journey from field to fork. They collected spinach leaves from processing plants. They frightened cows near fields of greens to induce defecation and collect their manure. They dipped beakers into water used to irrigate farms or wash the spinach.
Identification codes printed on the bags of leftover spinach led detectives to their first breakthrough: they had been packaged on Aug. 15 at a San Juan Bautista plant operated by Natural Selection, one of the nation's biggest purveyors of bagged salads. The company had already issued a voluntary recall.
However, exhaustive testing of the plant's equipment and water supply turned up none of the virulent strain of bacteria, according to health officials and Natural Selection.
Attention then turned to the fields. Using the company's records, investigators traced the spinach packaged that day to nine farms. Codes on more contaminated spinach packages then narrowed the search to four fields, Cabaluna said.
By early October, the death toll had risen to three.
The FDA said the O157:H7 strain had been found in manure on a cattle ranch within a mile of spinach fields. Investigators combed the pastures, gathering more samples, including wildlife and cattle feces.
Last week, health officials said six new samples from the ranch tested positive for O157:H7, including one found in the guts of a feral pig that was killed on the property. There were also signs that pigs had broken through a fence to feast on spinach, pointing to that field as a likely source of the outbreak and to the wild pigs as probable carriers.
However, officials said they're not ruling out that other fields may also have been a source of bacteria. Investigators continue to look at three other ranches in the area, and are still looking at water, fertilizer and other wildlife, including deer, as possible sources, officials said.
Whatever the final conclusion, this investigation has already provided the most specific information to date for how a microscopic organism commonly found in animal feces can sicken and kill consumers thousands of miles away.
"We've never found that in past investigations," Dr. Kevin Reilly of the California Department of Health Services said Thursday.
He also noted that no one has become ill from eating contaminated spinach since Sept. 25.
"All evidence points to this outbreak having concluded," Reilly told reporters.