Of microbes and milk; probing America's worst salmonella outbreak

FDA Consumer, Feb, 1986 by Chris Lecos

Of Microbes and Milk: Probing America's Worst Salmonella Outbreak

Large, refrigerated tanker trucks no longer rumble through the streets of Melrose Park, Ill., to Deliver their 40,000- to 50,000-pound loads of milk to the Hillfarm Dairy. The dairy at one time processed about 1.5 million pounds of milk a day, but not a drop has flowed through its maze of nearly five miles of stainless steel pipes almost a year now. The huge silo-like storage tanks that rise above the plant's rooftop are readily visible to any casual passer-by, but they stand there today as empty monuments to the worst outbreak of Salmonella food poisoning in U.S. history.

Located in a thriving industrial area of this Chicago suburd, the dairy was the sole supplier of milk to 217 supermarkets operated by the Jewel Food Stores chain in Illinois, Indiana, Iowa and Michigan. The dairy, also owned by the Jewel company, had been producing milk there since 1968.

The outbreak that prompted the company to cease all dairy production on April 9, 1985, began with a scattered trickle of patients into Chicago-area hospitals and doctors' offices in late March. It ended with a torrent of sick men, women and children, all stricken by an organism identified as Salmonella typhimurium. One of its microbiological characteristics was its resistance to certain antibiotics.

At least 16,284 persons are known victims of the outbreak, all but 1,059 of them from Illinois. The others lived in Indiana, Iowa, Michigan, Minnesota and Wisconsin. That is the number of culture-confirmed cases, meaning the Salmonella typhimurium strain that was contaminating the milk they drank also was found in stool samples from the victims. Patricia J. Larsen, a spokeswoman for the Illinois Department of Public Health, said the organism "directly caused" the deaths of two persons and was a contributing factor in the deaths of four, possibly five, others. The latter were people with other conditions that "presumably were aggravated to some degree by the infection," she said.

Thos are the official numbers, but most public health authorities agree that the actual totals are substantially higher. Many more people, it is believed, suffered diarrhea, fever, abdominal pain and cramps from drinking the milk but recovered quickly and never saw a doctor or reported their illness.

The Illinois outbreak triggered one of the most intensive investigations ever made of a milk-borne epidemic. What made it so frightening was the fact that thousands of people had become ill from drinking one of the most closely regulated products in the food supply. For years, milk has had the enviable record of being one of the nationhs safest foods because it was a pasteurized product.

It's not uncommon for unpasteurized milk to contain Salmonella or other organisms. But about 99 percent of the 280 million glasses of milk Americans drink every day is pasteurized. At most dairies, that means heating the milk to at least 161 degrees Fahrenheit for at least 15 seconds and then quickly cooling it--thus destroying microorganisms that could contaminate the milk. Milk safety experts with the Food and Drug Administration point out that less than 1 percent of all outbreaks of food poisoning reported in the past decade were caused by milk. And over the past 30 years, about 95 percent of those milk-related food poisoning incidents that did occur involved upnasteurized milk.

At the Hillfarm Dairy it was pasteurized, 2 percent (low-fat) milk produced under two brand names--Bluebrook and Hillfarm--that caused so many to become ill with Salmonella poisoning.

But when the investigation into the poisonings began, there was no certainty that the outbreak was due solely to low-fat milk, although it was the one product that many of the victims said they had consumed.

As investigators began their probe to find the source of the contamination, countless questions begged for answers:

Where did this unusual strain of Salmonella come from? Did it originate at one of the dairy farms that supplied the milk to Hillfarm? Was it brought into the plant by an unsanitized truck? Was the milk originally so contaminated that enough bacteria survived the plant's pasteurization process to contaminate the finished product? Was the contaminating organism resistant to heat treatment? Did someone purposely, or accidentally, introduce the organism into the plant?

The investigation determined that the same organism had caused at least three outbreaks of food poisoning in the spring of 1985 and other smaller, scattered outbreaks dating back to June 1984. Investigators believe an August 1984 outbreak, in which 200 people became ill, probably was related to consumption of Hillfarm products. However, later investigation failed to provide enough evidence for investigators to claim that the other 1984 incidents were similarly linked. Such reoccurrence, however, did raise the possibility that the organism had somehow persisted within the plant's environment for many months. What made it possible for this organism to intermittently--but not regularly--contaminate 2 percent milk but not whole or skim milk or any other products (chocolate milk, cottage cheese, ice cream, etc.) produced by Hillfarm?