The final report on the listeriosis epidemic that claimed 48 lives in Los Angeles County in 1985 traces California's worst food poisoning case ever to raw or poorly pasteurized milk used to make cheese at a now-defunct Artesia plant.
The report, published today in the New England Journal of Medicine, reaches that conclusion even though investigators never found the Listeria monocytogenes bacteria in the dairy herds that supplied raw milk to Jalisco Mexican Products Inc.
The investigators' failure to culture the bacteria from the herds' milk may reflect the timing of the samples, the authors said. It could also reflect low concentrations of listeria in the samples or the insensitivity of culture methods, they said.
The shortcoming "doesn't undermine the conclusion," said Dr. Laurene Mascola of the Los Angeles County Department of Health Services, an author of the report. "We still felt it was the raw milk. There was nothing else that was common or made biological sense."
An attorney for Jalisco's primary milk supplier, City of Industry-based Alta-Dena Certified Dairy, took sharp issue with the report's conclusion.
"Raw milk had nothing to do with the outbreak," attorney Raymond A. Novell said. "The (journal) report is incorrect."
Novell alleged that Jalisco's Artesia plant was contaminated and that this--not raw milk--was the source of the deadly bacteria. Among the problems at the Jalisco plant, he charged, was that the company used recycled "spoiled cheese" in its production process.
Health and law enforcement officials who had investigated the epidemic never pinpointed how the outbreak started--whether it was sparked by contamination from raw materials supplied to Jalisco, from unsanitary conditions in the plant or whether the plant's pasteurization methods were at fault.
"Certainly raw milk is a strong candidate as the source of the problem, but no one is certain at this point," said Thomas A. Papageorge, chief of the Los Angeles County district attorney's consumer protection division.
For his part, Jalisco's cheese maker, Jose Luis Medina, said he never knew what caused the epidemic.
Both Medina and Jalisco's owner, Gary McPherson, pleaded no contest in 1986 to misdemeanor criminal charges. They were sentenced to 60 days and 30 days, respectively, in Los Angeles County jail and fined a total of about $48,000.
The epidemic spawned about 150 lawsuits against Jalisco, Alta-Dena and the supermarkets that carried Jalisco's products. Lawyers estimate that a couple of million dollars in insurance settlements has already been paid out.
About 100 cases are still pending in Los Angeles County Superior Court. One of them, considered a lead case that could decide whether Alta-Dena has any liability, is expected to commence early next year.
Number of Deaths
The investigation, led by researchers from the federal Centers for Disease Control in Atlanta, counted 142 cases of human listeriosis between Jan. 1 and Aug. 15. The deaths included 20 fetuses, 10 newborn babies and 18 adults. State investigators who looked at cases from Jan. 1 to Nov. 2 found 40 deaths caused by the bacteria.
The New England Journal report noted that the Jalisco plant had been receiving 10% more milk than it had the capacity to pasteurize. They found that the pasteurizer operated properly but that it could be bypassed during cheese production.
Numerous samples of cheese produced between January and mid-June showed high levels of phosphatase, enzymes that indicate insufficient pasteurization or the introduction of raw milk into the process after initial pasteurization.
"The long period in which the cases occurred points toward the continual addition of a contaminated raw ingredient," the report states. "Alternatively, the organism could have been perpetuated in the plant environment after the initial introduction."
The authors note that soft cheeses and brined fresh cheeses may be an especially efficient medium for listeria. Recently, other refrigerated dairy products, such as Brie cheese, ice-milk mix and ice cream bars, have been found to be contaminated.
The 1985 epidemic prompted tighter regulation of the fresh-cheese industry; similar steps are being considered for dairy products in interstate commerce.