Doctors play role in tracking outbreak

Last month, disease detectives pursued a DNA fingerprint across 26 states, searching for clues to the source of an unusually widespread outbreak of Escherichia coli 0157:H7. An early match to a bag of fresh spinach in Colorado helped state and federal epidemiologists trace the culprit back to a California grower on Sept. 29 -- 15 days after the Food and Drug Administration advised consumers not to eat the leafy vegetable.

"This is not the first time molecular fingerprinting has helped track outbreaks," said Mel Kohn, MD, MPH, Oregon's state epidemiologist. "For us, an astute epidemiologist picked up a trend and zeroed in on spinach. When we presented our five initial cases to the Centers for Disease Control and Prevention, it matched information from other states."

The current outbreak, associated with 192 reported cases, including 30 cases of hemolytic uremic syndrome, 98 hospitalizations and two deaths, is not the first. There has been a long history of E. coli outbreaks involving leafy greens from the central California region.

"This is the 20th outbreak since 1995," said Douglas Powell, PhD, associate professor and scientific director of the Food Safety Network at Kansas State University in Manhattan. "For example, in 1996 there was the Odwalla apple juice E. coli outbreak. In 2005 there was a national recall of Dole bagged lettuce."

While parallel laboratory and epidemiological investigations are crucial in identifying the source of such outbreaks, the hunt begins with the patient and physician. Without physician involvement, early patterns and clusters may go unnoticed, giving the bacteria time to spread. "Physician reporting is at the basis of tracking these down," said Dr. Kohn. "It's a very important function."

Ideally, communication moving both ways between public health and practitioners enhances detection, says Jonathan Temte, MD, PhD, an associate professor of family medicine at the University of Wisconsin School of Medicine and Public Health in Madison. Wisconsin had the earliest confirmed cases in this latest outbreak.

"In a perfectly working system, the feedback loop is back to the clinician," says Dr. Temte, also a spokesman for the American Academy of Family Physicians. "In Wisconsin we have, although stressed, a relatively intact public health system. But the take-home message is that across the country our public health system is in shambles. For too long there's been a gap in ongoing collaboration."

Following the fingerprint

Here's what's known about the September outbreak.

Sometime in early August the first of 192 unsuspecting patients ate the contaminated produce. On Aug. 19, the initial case was confirmed. After this index patient, others followed, generally demonstrating an incubation period of four to five days after ingesting the culprit. On Sept. 7, a Wisconsin woman died from complications. By Sept. 8, state health officials alerted the CDC. It had a cluster.

CDC PulseNet -- the national genetic fingerprint tracking database created in 1993 after an E. coli outbreak linked to tainted hamburger killed four -- kicked into action, logged the DNA fingerprint and was poised to match others. On Sept. 12, PulseNet confirmed that the E. coli 0157:H7 strains from infected patients in Wisconsin had matching pulsed-field gel electrophoresis patterns. By Sept. 13, Dr. Kohn's office in Oregon, still unaware of the Wisconsin cases, called the CDC. The DNA from both of these states were ultimately shown to exhibit the same pattern in patient isolates. Additionally, more matches were beginning to emerge from other areas. And so the chain of events began to take shape. Early Sept. 14 a public warning was issued. The next day voluntary recalls of spinach began and stores cleared their shelves of the potentially deadly produce.

The CDC Outbreak Response and Surveillance Team and OutbreakNet, the network of public health epidemiologists who investigate foodborne disease outbreaks, joined other health officials in the search. At the same time, a CDC hydrologist from the National Center for Environmental Health was deployed to California, joining FDA officials in the suspected region. By Sept. 29, the spinach trail led to Natural Selection Foods, in San Juan Bautista, Calif.

Nonetheless, the FDA, CDC and the state of California continue to investigate the cause, including ongoing inspections and sample collection in facilities, the ground and water, as well as studies of animal management, water use and the environment.

Additionally, FDA and FBI agents executed search warrants Oct. 4 for certain spinach growers and distributors in an effort to gather facts about the outbreak. U.S. Attorney Kevin V. Ryan offered reassurances that there is no indication of deliberate contamination. "We are investigating allegations that certain spinach growers and distributors may not have taken all necessary or appropriate steps" to ensure the product was safe before it went to the marketplace.

Natural Selection Foods issued a statement the same day pledging cooperation. "[We] welcome all efforts to trace this problem back to its source," said Charles Sweat, the company's chief operating officer. "We continue to believe that the source of the contamination was in the fields. ... While we have always maintained the highest level of food safety standards, last week we implemented a set of aggressive and unprecedented measures to help assure that no contaminated product, spinach or anything else, will enter our processing operation again."

Meanwhile, the FDA and the state of California have previously expressed serious concern over continuing outbreaks of foodborne illness associated with the consumption of fresh lettuce and other leafy greens.

"The FDA has been warning these growers for several years," said Dr. Powell. Still, eradicating the bug is not easy. E. coli O157:H7 lives in a natural reservoir existing in cattle, sheep, goats and deer, which can contribute to water or soil contamination.

Once in the soil, the bacteria can survive for months. So a crop could be clear, but when the seeds are planted, the plant is infected. To further complicate things, theoretical evidence now indicates that the bacteria can enter plants through their roots. "It enters the plant's vascular system and just washing is not enough," he said.

Following the latest outbreak, FDA and state officials have asked the industry for a plan to minimize the risk of a repeat. "The first line of defense is on the farm. The industry is only as good as its worst grower," Dr. Powell said. "The light out of this outbreak is it ... captured attention and maybe now something will get done."