Source of Contamination Elusive in Jalisco Probe

More than two months after investigators traced an epidemic of listeriosis to a company called Jalisco Mexican Products Inc. of Artesia, they have still not answered the bottom line question: How did it happen?

Although health officials can say with certainty that soft cheese produced by Jalisco caused the biggest food poisoning case in California history in terms of illnesses and fatalities, no one can say for sure how the cheese became contaminated.

Among those attempting to answer that question are the U.S. Food and Drug Administration, the Centers for Disease Control in Atlanta, and the Los Angeles district attorney’s office, which has threatened criminal action against the company and its officers if findings support it.

Investigators say uncovering the contamination source is critical to building any sort of legal case.

Government testing has located the dangerous Listeria monocytogenes bacteria in Jalisco’s cheese, but nobody--including the FDA and the state Department of Food and Agriculture--has yet found Listeria bacteria in the milk that was supplied to the cheese firm.

(An experimental method used at the University of Vermont did find Listeria bacteria in some of the milk supplied to Jalisco, but the test is too new to lead to any conclusions, according to a scientist who supervised the test.)

In Atlanta, Centers for Disease Control scientists are conducting a much more painstaking test of milk samples from all 27 Southern California dairy herds that supplied Jalisco--a “cold enrichment,” or refrigerated, test that takes six weeks or longer to produce results. Tests performed by the FDA and the state took two weeks or less.

So far, the Centers for Disease Control have found no solid evidence of Listeria monocytogenes in the hundreds of milk samples being scrutinized.

But Dr. Michael Linnan, a Centers for Disease Control epidemiologist who was chief of a special team from the Atlanta centers summoned to Los Angeles to investigate the epidemic, said in a telephone interview that he fully expects to find the illness-causing bacteria in some of the cows owned by Jalisco’s milk suppliers.

Based on what he knows about the incidence of Listeria in dairy herds, Linnan said, “The most probable mechanism of contamination is that it came into the (Jalisco) plant in the milk. I believe ( Listeria monocytogenes ) has been present in California milk” for a long period of time.

Generally agreeing with this view is John Silliker, a Carson-based microbiologist retained by Gary S. McPherson, Jalisco’s president.

Silliker said he is positive “unpasteurized milk got into the (Jalisco) product” and that “anytime you use raw milk, there is the probability you will be exposed to pathogenic microorganisms, including Listeria (bacteria).”

Silliker said he found levels of Listeria monocytogenes in his own tests of Jalisco’s cheese, similar to those performed by the FDA, but that the levels were “very low.”

Some state agriculture officials suggest that they are becoming more and more skeptical because of the length of time it is taking the Centers for Disease Control to complete the milk tests.

“What they are doing is not the way things are happening in the real world,” said Hans Van Nes, the Department of Food and Agriculture deputy director. “The growth of bacteria would be expected.”

This is not the first time that a listeriosis epidemic has stumped investigators.

In August, 1983, listeriosis swept across Massachusetts, infecting 49 victims and killing 14 of them.

Investigators ultimately found the source for the epidemic: milk pasteurized at one clean, modern plant. But pasteurization, or briefly exposing raw milk to high heat, is supposed to kill harmful bacteria, according to the FDA.

So how did the potentially deadly bacteria survive?

“We cannot with precise certainty say what happened in Massachusetts,” said Dr. David W. Fleming, who headed the Centers for Disease Control investigation there.

Although Listeria monocytogenes was described for the first time in 1926 by three Cambridge University researchers, its characteristics and how it is transmitted to humans are still not fully understood. So with the Massachusetts outbreak fresh in mind, the FDA, without fanfare last October, embarked upon its first nationwide Listeria investigation.

Strains of Bacteria Found

As a result, in April, an FDA team turned up five strains of Listeria in 100 milk samples taken from cowherds in the Sacramento area. Four of the strains were innocuous, according to an FDA microbiologist in Cincinnati who examined them, and the fifth produced mild illness in laboratory rats. Ultimately, FDA scientists found that as many as 10% of all cows sampled nationally were Listeria carriers.

At about this time, Los Angeles County health officials began picking up signals indicating that a major Listeria epidemic was starting to roll through the area and that its victims were primarily Latinos.

Jalisco cheese was identified as the cause. The plant was shut down, its products recalled. Despite extensive testing of soft cheeses produced by other makers, no other cheese was ever connected to the wave of illness.

Both the FDA and the Los Angeles County district attorney’s office have been conducting separate investigations into Jalisco’s cheese-processing operations.

Under its federal powers, the FDA’s efforts could result in a criminal prosecution of the firm and its officers, but any penalties it might seek on conviction would result in misdemeanor--not more serious felony--penalties.

Liability Cited

“Under interstate commerce,” said Abraham Kleks, director of the FDA’s Los Angeles district office, “if you introduce a contaminated product, you’re liable, and it’s a violation of the FDA’s strict liability laws because one doesn’t have to show intent (to contaminate).”

The county prosecutor, however, has the authority to seek felony conviction and punishment in the Jalisco case.

No one is currently suggesting that any Jalisco officer or employee deliberately contaminated the firm’s cheese products, which were marketed nationally.

Therefore, deputy prosecutor Clifford Klein, who is in charge of the Jalisco case, said “the most serious thing under investigation” is a potential felony charge of involuntary manslaughter. A conviction on that charge could lead to up to four years in prison.

But again, investigators must isolate what happened. And, so far, it appears that neither FDA official Kleks nor Klein, who works in the prosecutor’s consumer protection division, has pinned down the cause of the contamination with any certainty.

On June 26, Dist. Atty. Ira Reiner produced records for reporters which, he said, showed that the amount of raw milk received at the Jalisco plant between April 1 and June 12 far exceeded the capacity of the firm’s pasteurization machinery for that period.

Therefore, if Centers for Disease Control tests eventually support Linnan’s assumption that the Listeria bacteria were present in some of the herds that supplied Jalisco, the focus of the investigation would shift to Jalisco’s pasteurization process and how it allowed contaminated milk to reach the finished product.

Machinery Apparently OK

As for the pasteurization machinery itself, although it was several years old, it was working properly when examined, both FDA official Kleks and Darrell D. Cole, regional vice president of APV Crepaco Inc. of Cerritos, the firm that manufactured the equipment, told The Times.

Few on the medical side of the investigation believe that there was post-pasteurization contamination of the cheese even though FDA investigators found Listeria bacteria in the Jalisco plant.

“It is very unlikely that a source within the plant itself (such as accumulation of Listeria bacteria on a table top) could (sustain) the epidemic for months,” said Linnan of the Centers for Disease Control.

Furthermore, there is no evidence that Jalisco’s employees carried above-average levels of Listeria bacteria in their systems, said Dr. Shirley L. Fannin, chief of Los Angeles County’s communicable disease control program.

But there can be no doubt about the outbreak’s deadly impact.

38 Deaths

Florence Morrison, statistical chief in the infectious diseases section of the state Department of Health Services, said 98 persons became ill statewide from eating Jalisco’s soft cheese products, and 38 of these individuals died. More than half of these fatalities--22--occurred in the Los Angeles area.

(The figures are much lower than those that circulated earlier in the epidemic. Government agencies were initially providing data that included all Listeria illnesses and deaths rather than only those cases connected to Jalisco.)

It is not yet clear when the multiagency investigative effort can be concluded. The FDA will soon send its report to the district attorney, but it may take the Centers for Disease Control a few extra weeks to be sure--one way or another--about the dairy herd samples.

Jalisco chief executive McPherson, under advice of his criminal attorney, will not comment on how he thinks his cheese products became contaminated.

In any case, said McPherson, a former accountant, “I’m an administrator; I’m not a cheese maker.”