The persistence of a Cornell University researcher and the prompt use of his unique database are credited for helping limit the death toll in a recent outbreak of Listeria monocytogenes, a virulent food-borne pathogen.

Between last October 1998 and Feb. 2, 1999, 11 people died nationally -- three of them in New York state -- and more than 70 became ill as a result of eating food contaminated with a rare strain of the bacterium, called type E. The efforts of Martin Wiedmann, a Cornell food science research associate, led the Center for Disease Control (CDC) in Atlanta to determine the cause of the outbreak. As a result, a major food-processing company voluntarily made what some have estimated to be the largest food recall in American history.

The credit for much of this action goes to Wiedmann, says Dale L. Morse, director of the Division of Infectious Diseases at the New York State Department of Health. "I wonder if the outbreak could have been recognized so quickly or even if it would have been recognized at all," he says. "Because of Martin's effort, we were able to link seven cases together early, clarify that there was an outbreak of a certain strain, identify it and where it came from early. Without this effort, the strain may never have been identified."

Listeria's ability to kill is greater than that of the bacteria E. coli O157:H7, Salmonella, and Campylobacter combined. In 1998, according to the CDC, theE. coli strain caused 70 deaths out of an estimated 10,000 to 20,000 cases of food-borne illness nationally. By comparison, in 1998 L. monocytogenes caused 250 deaths out of a total of 1,100 infections.

Wiedmann has been collecting samples of the bacterium L. monocytogenes for seven years and identifying each strain's unique genetic fingerprint. Every month the New York state health department sends him up to six strains, which he identifies and adds to a database. He also receives Listeria strains from tainted food sent by the New York State Department of Agriculture and Markets and strains isolated from animals from the New York State Veterinary Diagnostic Laboratory. Wiedmann has developed a Listeria database of nearly 800 strains.

Until last October's outbreak of the disease, called listeriosis, neither Wiedmann nor Kathryn Boor, Cornell assistant professor of food science, appreciated the true value of the Listeria fingerprint database. "We were collecting molecular fingerprints with the goal of learning more about the diversity and basic biology of L. monocytogenes strains, but we did not fully anticipate the role that this database could have in immediate human health applications," says Boor.

Typically, there are up to six cases of listeriosis a month in New York state, normally caused by different strains of L. monocytogenes. But late last October, Wiedmann received 15 samples of Listeria -- more than double the normal amount. The samples were sent to Mary S. Bodis, a research support specialist in the laboratory of Carl A. Batt, Cornell professor of food science, for ribotyping, a method of determining genetic fingerprints.

Seven of the 15 samples had identical genetic fingerprints, meaning that the same strain had caused the illness in seven people. Wiedmann sent the information to the New York State Health Department and the CDC. The federal agency also had noticed a rise in the number of Listeria cases, but until Wiedmann's fingerprints, they didn't know which strain to look for.

The CDC traced the latest outbreak to consumption of hot dogs and was able to locate and test one of the contaminated products. It was found to be positive for the L. monocytogenes Type E strain. The contaminated hot dogs had been made by Bil Mar Foods, of Michigan, a subsidiary of Sara Lee Corp. Bil Mar Foods immediately issued a voluntary recall.

"This is a convergence of basic science and a real-world application. Before, we were collecting the molecular fingerprints of the strains for research purposes. Clearly, now, we're on an exciting track," says Boor.

Prior to using DNA-based identification, food samples had to be collected and examined for the presence of bacteria. The researchers then used process of elimination to categorize the organisms in an attempt to find which one was linked to the disease, a process that took many weeks. Now, thanks to ribotyping and other methods, such as polymerase chain reaction, the identification and typing processes have been greatly speeded up.

Says Boor, "It would have taken longer to make the link. Martin's finding pointed the CDC in the right direction, shortened the length of the time to find the strain. To implicate Listeria so fast and to find food bearing the same strain still in the system was fantastic."