Weeks later, E. coli outbreak still a mystery

The victim count, and the trail of evidence, continue to grow, as investigators probe the ongoing deadly outbreak of E. coli bacteria.

So far, 187 people have taken ill, including about 30 cases of kidney failure, and at least one death is blamed on the outbreak. But how the E. coli contaminated all that spinach remains a mystery.

Despite its wilted image, spinach was back in the produce section Friday. Several grocery chains on the East Coast are re-stocking with spinach grown in Colorado and Canada.

In California, the packing house implicated in the outbreak now says it will regularly test produce for E. coli. It's also reaching out to victims of the outbreak.

"We will be offering them reimbursements for their out-of-pocket medical expenses," says Natural Selection Foods Chief Operating Officer Charles Sweat.

So far health officials have found no problems at the plant. They're also investigating nine farms in three counties that supplied spinach to the packer.

The E. coli could have come from nearby livestock through contaminated irrigation, or perhaps spread by workers.

What makes it difficult for investigators is that by the time they reach the suspected fields they are either plowed-under or replanted with different crops. And workers have gone on to other jobs, so the odds of finding the source of E. coli are extremely slim.

After 20 outbreaks over 11 years, they've never traced the source of an outbreak to a farm.

"I would be surprised if they did find the exact E. coli in the field," says Dr. Linda Harris, a professor at the University of California, Davis.

It's frustrating for California farmers like Joe Pezzini, whose spinach crop has not been implicated.

"We are wondering day-by-day if our product will go to market," he says.

Growers already use federal guidelines for farm practices like worker hygiene and irrigation water quality, and those guidelines are now being tightened.

"All these efforts, voluntary efforts on the industry's part to date, have not been good enough," says Kevin Reilly, deputy director of the California Department of Health.

And if they don't improve, officials fear it's just a matter of time until the next outbreak of E. coli.