Last week, salmonella poisoning was linked to a suburban Chicago Burger King. Earlier this month, Kraft's Polar B'ars ice cream was recalledXL due to contamination by the same bacteria that killed more than 80 people in California last year.

What these incidents represent is a larger phenomenon occurring in the United States' food supply. Over the past several years, there has been a resurgence of microbial contamination and an increase in the number and severity of foodborne disease outbreaks.

In fact, government regulators such as Frank Young, commissioner of the Food and Drug Administration, and Sanford Miller, director of the FDA's Center for Food Safety and Applied Nutrition, believe that bacterial contamination poses a far greater risk than chemical additives and preservatives in food.

Microbial contamination has been a "continuing and nonremitting problem," said Young, who said that foodborne illness is a major FDA priority and "will be an increasing one."

The numbers are revealing. While the Centers for Disease Control reported 19,300 cases of confirmed foodborne diarrheal disease in 1982, anywhere between 24 million and 81 million cases actually occur per year, according to the estimates of Douglas Archer, director of microbiology at FDA, and John Kvenberg, FDA's deputy program manager for microbiology.

Archer and Kvenberg also estimate the economic loss due to medical care and lost productivity at between $5 billion and $17 billion annually. The passive reporting systems of government surveillance programs have historically underestimated the incidence numbers, Archer said.

The reasons for the emergence of these pathogens -- or microorganisms that can cause disease -- are numerous.

Some scientists believe that there has not been an actual increase in foodborne pathogens but simply an increase in technology's ability to detect them.

And once a new pathogen is discovered, there is an tendency for clinicians to look for more of it -- and they'll usually find it, said Archer. In addition, Archer said, bacteria are always "changing and evolving."

Another factor is the enormous size of food factories and the length of the distribution chain. Food processed in one state is now shipped and eaten by individuals across the country and the result is increased possibilities for mishandling along the way.

*Speaking to the dairy industry recently, Jerome Kozak, chief of the milk safety branch at FDA, said that one error in today's large dairy operations can cause an epidemic. New technology and the complexity of these plants is exceeding the agency's ability to adequately assess their safety, Kozak said.

Some pathogens thrive during the heyday of certain food trends such as sushi and raw bars. Fancy carryouts, deli cases and undercooked foods offer increased opportunities for time and temperature abuses, which are attractive breeding conditions for certain disease-producing bacteria.

And some observers note that changes in the nuclear family have led to a population of diverse home food handlers who may not be attuned to basic food sanitation practices. Some government statistics cite the home kitchen as the place where the majority of mishandling that leads to foodborne disease occurs.

Some scientists believe that because animals receive antibiotics in their feed -- to make them grow bigger faster -- drug-resistant bacteria have developed. These strains are then thought to be passed on to humans, where they decrease the body's ability to respond to antibiotic therapy. Certain strains of salmonella and campylobacter, for instance, are resistant to antibiotics, a situation that people such as Carol Tucker Foreman, consumer advocate and former assistant secretary of agriculture, said poses a "very serious problem" to immune-suppressed individuals.

Foreman, other consumer advocates and a report issued by the National Academy of Sciences also stress that the current meat and poultry inspection system provides inadequate procedures to detect microbial contamination. Foreman said that the "Gramm-Rudman compulsion" to save money is likely to further reduce the quality of meat inspection and "almost eliminate the chance that it will be done better."

The types of pathogens cropping up in foods, the insidious paths they follow and the specialized, susceptible segments of the population they are attacking are as complex and numerous as the reasons for their appearance.

Among formerly rare bacteria that are now being detected with increasing frequency, listeria monocytogenes -- the culprit in the more than 80 California deaths tied to Mexican-style cheeses, the Polar B'ars, brie cheeses imported from France this year and several other incidents -- has caused some of the greatest concern.

There have been no documented cases of listeriosis -- the disease caused by the bacteria -- linked to Polar B'ars or any of the brie shipments, according to the FDA. However, the California outbreak was discovered after spontaneous abortions caused by listeriosis occurred in women consuming Jalisco brand cheese. The cause of the contamination was believed to be raw milk used in the processing of the cheese.

The bacteria, in fact, thrives in the systems of small children, pregnant women and their fetuses, frail, elderly individuals or other persons with weak immune systems. According to the FDA, it poses no threat to healthy individuals.

In addition, there has been considerable concern at the FDA recently over a preliminary study from the Food Research Institute that reported that the bacteria may be able to survive pasteurization.

Other foodborne outbreaks being connected to dairy products have prompted the FDA to increase its surveillance of the dairy industry. The program includes more thorough dairy plant inspections and more intensive training programs to alert dairy industry personnel to the public health consequences of potentially pathogenic bacteria in milk products.

Food poisoning traced to the Hillfarm dairy in Chicago last year resulted in the country's worst salmonella outbreak, which caused the deaths of two persons and confirmed sickness in over 16,000.

Investigators concluded that the probable cause of the incident was that unpasteurized, possibly contaminated, milk was inadvertently carried through pipes that connected to the pasteurized milk.

In fact, part of FDA's increased surveillance program calls for a review and evaluation of critical control points and possible routes of contamination of post-pasteurization blending operations.

Another bacteria, yersinia enterocolitica, has also been associated recently with a few isolated incidents of foodborne disease due to contaminated milk.

It's certainly not just dairy products, however, in which these pathogens are harboring. Raw shellfish are also culprits. Between 1911 and 1977, there were two reported cases of vibrio cholera. Since 1978, there have been several reports of human illness due to the pathogen, most of which were traced to consumption of raw oysters and clams.

Other pathogens -- such as salmonella -- which have long been known to be foodborne disease culprits are appearing with increasing frequency.

According to USDA estimates, about 37 percent of all poultry contains the salmonella bacteria, which is carried via various husbandry and processing methods used by the industry.

"The USDA will give you consumers a dozen ways how not to get sick from salmonella-infected poultry ," said Foreman. But "the USDA abdicates its responsibility when it says, 'you take care of it, it's not our responsibility,' " she continued.

"We don't ever say that," said Lester Crawford, associate administrator of the USDA's Food Safety and Inspection Service. "These organisms are ubiquitous and not eradicable," Crawford said. "We have to figure out a way to live with them with the least microbiological burden on the human population." Crawford added that the USDA is exploring techniques to deal with decontamination of salmonella-infected poultry, including ascetic acid washes and irradiation.

Still other pathogens -- although certainly not new to the environment -- have only recently been connected to foodborne disease. Escherichia coli -- a normal inhabitant of the intestinal tract -- has recently been found to be capable of causing gastrointestinal disease; some of the documented food outbreaks have been associated with undercooked ground beef.

Advanced culture methods have allowed scientists to identify campylobacter, which now accounts for more foodborne infections than salmonella. Transmitted by contaminated raw milk, unchlorinated drinking water, undercooked chicken, raw shellfish and mushrooms, it was found by the FDA to be in 20 percent of sampled chicken carcasses and 83 to 94 percent of turkey carcasses.

Discoveries are also being made that show that some bacteria produce multiple toxins. Through DNA technology, scientists have found that the cholera bacteria, for example, may have the ability to produce two -- or possibly more -- toxins.

Furthermore, other pathogens are being discovered in foods that were previously untraditional carriers.

While the organism clostridium botulinum -- which causes botulism -- has traditionally been associated with canned foods, there have been a few incidents in which the toxin has been produced in surprising environments.

In 1983, for example, saute'ed onions kept warm on a stove for an extended period at a Peoria, Ill., restaurant, caused botulism in about 30 individuals and one death. Commercially packed chopped garlic in soybean oil, used to make garlic butter at a Vancouver, B.C., restaurant, resulted in 27 cases of botulism, and there have been three U.S. outbreaks in which potato salad was the carrier.

Special populations -- such as pregnant women, the elderly, cancer and AIDS patients -- have been shown to be particularly -- and often dangerously -- susceptible to foodborne bacteria, as their immune systems are not able to defend against the invading pathogens.

In addition, said Archer, there is definitive evidence that episodes of diarrhea caused by foodborne pathogens may contribute to rheumatoid and kidney diseases.

Diarrheal disease is also reaching "alarming proportions" among children in the nation's day-care centers, according to an article in FDA Consumer. Many cases can be traced to staff who change children's diapers and then handle food served to the children, the article stated. Some of these cases, Archer said, have involved prolonged diarrheal illness.

*Despite the presence of these pathogens, government officials maintain that the United States has the safest food supply in the world, and that efforts are simply being made to make it safer. It is not the food that is inherently unsafe, Archer concludes, but what people do by mishandling it.

Nevertheless, much research still needs to be done. An article in the New England Journal of Medicine regarding the consumption of raw shellfish states that there is a lack of methods available to detect the pathogenic intestinal viruses in water, shellfish and in humans. Dr. Mitchell Cohen, assistant director for medical science of the bacterial disease division at the Centers for Disease Control, said that there are still a lot of foodborne disease outbreaks in which the specific bacteria that caused the illnesses have not yet been identified.

In addition, said Young of FDA, methods of analysis must be updated so that the extent and significance of foodborne contamination can be detected more rapidly.