Researchers Wage Two-Front Battle Against Listeriosis
In the year since California’s worst outbreak of food poisoning--the epidemic involving tainted Jalisco cheese--efforts to prevent a reoccurrence have focused on two fronts: tightening surveillance of the nation’s cheese and dairy industries and designing a speedier test that could warn the public of potentially deadly food products.
At the same time, research sparked by the California outbreak is suggesting that federal standards and regulations governing milk pasteurization and cheese production need overhauling.
The California killer was Listeria monocytogenes , bacteria identified more than half a century ago. The disease produced by these bacteria, listeriosis, can cause inflammation of brain membranes, such as occurs in meningitis, and can be lethal when the body’s immune system is weak.
Once the Mexican-style soft cheese products of Jalisco Mexican Products Inc. of Artesia had been identified as the carriers of Listeria bacteria, government investigators scrambled for the precise cause of the contamination.
Source Not Uncovered
But, as with listeriosis outbreaks linked to food poisoning in the Canadian Maritime provinces in 1981 and in Massachusetts in 1983, the contamination source was never uncovered. All that a blue-ribbon panel of listeriosis experts and investigators could conclude was that something went wrong in the Jalisco plant.
Of the 40 deaths connected with Jalisco cheese products recorded by the state Department of Health Services between January and August of last year, mostly in the Los Angeles area, 38 of the victims were either fetuses or infants; two were adults.
Through the first six months of this year, 95 cases of listeriosis have been reported in California, about the same rate as 1985 when the Jalisco figures are removed from the statistics. But because no pre-1985 data is available, “it’s impossible to draw conclusions,” said Florence Morrison, chief statistician for infectious diseases in the state Department of Health Services.
Dr. Shirley L. Fannin, deputy director of Los Angeles County’s communicable disease control program, said, “There’s no indication of unusual activity” this year in terms of reported listeriosis cases.
The Jalisco case concluded with the now-defunct firm’s president and its pasteurizer being sentenced to brief jail terms earlier this year on several misdemeanor counts.
But as the Jalisco investigation was concluding in December, another investigation was just beginning for public and private health professionals.
Armed with the scant information the scientific community had been able to develop over the decades, government and private investigators knew that Listeria monocytogenes was ubiquitous in the environment and could easily adapt to milk and cheese products. But they did not have a method of quickly identifying the bacteria nor were they completely sure of how to control its transmission to humans.
The Jalisco case has accelerated efforts to find these answers.
However, Food and Drug Administration Commissioner Frank E. Young underscored in a telephone interview that the public should not be misled into believing that listeriosis has become a burning national health issue.
Little Risk Cited
“For the vast majority of us, there is no risk,” said Young, who also is a microbiologist.
“The bottom line,” he said, “is that it’s not a very significant disease-producing organism. But given the right host condition, in very rare instances, it can produce death, and thus it is an organism to be reckoned with.”
Hence, Young said, California’s Jalisco epidemic, and last year’s major salmonella food poisoning outbreak in the Midwest, told the FDA that “it was time to look at dairy and milk products. . . . The public safety is an important issue that the FDA is responding to.”
Young ordered nationwide testing for Listeria monocytogenes and other dairy-oriented bacteria, which so far have not produced anything like another Jalisco-type outbreak.
With the exception of three Arizona cases of listeriosis possibly, but not positively, linked to a small Los Angeles-area cheese producer, FDA officials said their investigations this year have found no illnesses connected to any particular Listeria -contaminated product.
Such findings relieved FDA officials, who were not sure what this first big examination of the nation’s dairy industry would uncover.
“I’m awfully pleased,” said Douglas Archer, director of the FDA’s microbiology division in Washington, of the results so far. “We were quite concerned after the California (epidemic). At first, we thought we might be opening a can of worms.”
Archer’s observation was based on the results of three FDA examinations:
- FDA inspections of milk and ice cream plants.
Between April 1 and Aug. 15, 283 inspections were completed of milk and ice cream manufacturers throughout the United States. Eight plants--or 2.8% of those examined--had Listeria monocytogenes in their products, and recalls were initiated by the companies.
The firms, according to the FDA, were Jerseymaid Milk Products of Los Angeles; Crystal Food Import Corp. of East Boston, Mass.; Marigold Foods Inc. of Minneapolis; Shepp’s Dairy of Dallas; Gustafsen Ice Cream of Rice Lake, Wis.; Borden Inc. plants in Milwaukee and Miami; and Knudsen Corp. of Glendale, Ariz.
Criticism of FDA
The findings have generated some criticism that the FDA was not as conscientious as it should have been in warning the public.
Any product recall falling into the FDA’s Class 1 “life-threatening” category automatically triggers a public warning, said James Greene, an FDA spokesman in Washington. “Our responsibility is to assure the public that the products it buys are safe. Sometimes we’re accused of acting too slowly. And sometimes we may be guilty of that. The system is not perfect.”
According to FDA records, the agency or state officials publicly announced the contamination results in the Crystal Food, Marigold, Shepp’s and Gustafsen cases.
Because it took 15 weeks to test for Listeria bacteria in the Knudsen case--normally it takes about two weeks--FDA chief Young said his agency “didn’t know” if it had discovered anything dangerous or if the product had become contaminated during testing. By then, it had been consumed and no illnesses had been reported. So no public announcement was made, he said.
In the two Borden cases in Wisconsin and Florida and the Jerseymaid finding in California, Young said that under a milk agreement with those states it was left to state agriculture officials to determine whether a public warning was necessary.
In all three instances, state investigators could not find Listeria bacteria when they performed similar tests, the product was consumed without any illnesses being reported and no public announcements were made.
Of his agency’s decision to say nothing publicly about the FDA’s Jerseymaid finding, Hans Van Nes, a deputy director of the California Department of Food and Agriculture, said: “In our judgment we were satisfied there was no problem. We didn’t go out and try to scare everyone to death.”
Since April, said FDA milk safety branch chief Jerry Kozak, inspectors have been tearing dairy plants apart to examine machinery and reviewing pasteurization and sanitation records. “We’re trying to detect problems in the plant before someone (outside) gets ill,” he said.
And for the first time, Kozak said, FDA agents are involved in systematic microbiological surveillance--sampling finished products such as cheese and ice cream for evidence of Listeria bacteria.
Questions to Answer
“We’re trying to establish where there’s a significant health problem in the dairy industry,” Kozak said. “Or are there aberrations? Or are we dealing with new types of problems that we didn’t have before? That’s why we need this data.”
Apart from the FDA’s national efforts, the California Department of Food and Agriculture, armed with a new dairy inspection law spawned by the Jalisco epidemic, has hired a special investigator and a new auditor to act as industry watchdogs.
Stepped-up inspections of cheese plants and cowherds are part of the tougher state program to prevent another epidemic, a spokeswoman said.
- FDA inspections of domestic cheese plants.
The probe, begun in July, 1985, and concluded Sept. 30, 1985, involved the FDA’s inspection of 267 manufacturers of soft cheeses in 22 cities nationwide, including Los Angeles.
Of 553 cheese samples collected in this survey, two were contaminated with Listeria monocytogenes bacteria, the FDA reported. The samples, pieces of Camembert and lederkrantz cheese, were produced by a General Foods plant in Van Wert, Ohio. After a public warning and product recall, the agency allowed the plant to resume production.
An FDA report on inspections of 154 cheese firms in Wisconsin and Minnesota is expected to be released soon.
- FDA inspections of imported cheeses.
Begun in April, the ongoing survey has triggered product recalls of several brands of semi-soft cheeses, particularly Brie.
The recalls were the result of testing about 583 samples from 14 countries, mostly from France. In 19 instances--or 3.2% of the samples--cheese products were found to be contaminated with Listeria monocytogenes . In all cases, the FDA issued public warnings.
Last May, the French government negotiated an agreement with Washington that would require French food officials to certify that cheese exported to the United States is free from harmful Listeria bacteria.
Second Front of Fight
The second front of the fight against Listeria monocytogenes has been accelerated research aimed at a better, faster test to discover the bacteria in food products and to re-examine whether government standards and rules governing cheese production are adequate or outdated. Central to protecting the public from Listeria food poisoning is accelerated research into finding a quick method to discover the contamination, food scientists agree. Such a test is critical to preventing contaminated food from getting into consumer hands.
“People are putting a lot of effort into quick-culture methods,” said Dr. Claire Broome, an official with the Atlanta-based Centers for Disease Control, who helped investigate the Jalisco epidemic.
Her reference was to research being conducted at the Centers for Disease Control, FDA and schools such as the University of California, Davis, where experiments are being conducted with “gene probes” that could lead to a scientific breakthrough: an almost instant test for Listeria monocytogenes bacteria.
Under this method being developed by Dr. Dwight Hirsch, a UC Davis veterinarian, and others, a specific gene is isolated from Listeria bacteria. That gene is then inoculated to induce it to produce large amounts of the bacteria. Then the genes in the bacteria are “tagged” with a radioactive substance or color-dyed so that they can either be easily identified on X-ray film or under a microscope.
It can now take two to 10 weeks to grow a Listeria bacteria culture using a “cold enrichment” method, which involves refrigerating food samples for several weeks.
Dr. Robert B. Bushnell, another UC Davis veterinarian, said a number of Listeria bacteria studies are being conducted there, including what food preservatives, if any, will inhibit Listeria bacteria from growing and how great a dose of Listeria monocytogenes that it takes to make someone sick.
“I don’t see a repeat of last year,” Bushnell said of the epidemic. “Everyone is alert to the situation. The potential of this thing happening (again) is small.”
Separately, researchers at the University of Wisconsin are developing data suggesting that federal regulations and guidelines designed to kill Listeria bacteria will have to be rewritten.
During the height of the Jalisco epidemic, the FDA asserted that milk pasteurization--quick heating at 161 degrees Fahrenheit for 15 seconds--would kill the bacteria.
But now, according to Michael P. Doyle, an associate professor at the University of Wisconsin’s Food Research Institute, it takes more heat to kill this particular form of virulent bacteria.
After inoculating cows with Listeria monocytogenes , he said, milk from the cows was run through a pasteurizer using both the FDA standard and then exceeding the standard up to 165 degrees for 16.4 seconds.
Six out of nine times, the Listeria monocytogenes bacteria survived pasteurization at both the FDA temperature standard and the higher level, Doyle said. But no bacteria survived two tests when pasteurization temperatures were raised to a 170 to 172 degrees Fahrenheit range for 15.4 seconds, he said.
Yet, FDA milk safety chief Kozak is not convinced that the agency should instruct the nation’s food industry to raise pasteurization heating levels.
“If we determine that the (University of Wisconsin) work is valid, that will cause us to reconsider whether present pasteurization methods are valid,” he said. The agency, he said, may reach a conclusion next month.
Other federal regulations aimed at killing harmful Listeria organisms may have to be changed, too.
Another University of Wisconsin food researcher, microbiologist Elmer H. Marth, is suggesting that federal regulations governing how long certain cheeses should be held by producers to complete the ripening processes that kill harmful bacteria are not correct.
Under regulations now, he said, cheese made from raw milk, such as Cheddar, must be held for at least 60 days at a temperature not below 35 degrees Fahrenheit so that harmful organisms are killed by the natural cheese ripening processes.
But Marth said his recent research shows that Listeria bacteria could “survive for up to a year in natural Cheddar,” so that the ripening period should be much longer than 60 days.
“By no means is all Cheddar infected,” Marth said. But, he quickly added, federal rules designed to protect the public are outmoded and “ought to be looked at instead of people going merrily along their way.”