There are thousands of different bacterial, viral, parasitic and chemical agents capable of causing food-borne illness. Several of these, though, are identified as particular threats to the nation's food supply.
However, technological advances in food processing and evolving consumer eating habits provide opportunities for different pathogens to emerge as problems.
Many of the contaminants that concern health officials are naturally occurring and found throughout the environment. There is a consensus that some of these bacteria will not be eliminated regardless of efforts to control their growth. Mistakes in food handling, whether at the manufacturing or home level, can enhance conditions that may lead to outbreaks.
Salmonella is chief among the microbiological threats. There were 50,916 salmonellosis cases reported to the Centers for Disease Control in 1987, or the last year for which data is available. This figure vastly understates the actual number of illnesses by anywhere from 10 to 100 times, according to the CDC.
Not all salmonellosis cases are linked to food. In fact, many of the incidents do not have an identifiable cause. Even so, raw meats and animal byproducts are usually those commodities linked to episodes where a source is directly associated with contamination. Symptoms include nausea, fever, headache, abdominal pain and vomiting.
'Cooking the Only Protection'
"Salmonella cannot be eliminated from the raw, uncooked meat that we deal with," said Dr. Shirley Fannin, associate deputy director of disease control for Los Angeles County's Health Services Department. "Cooking is the only protection from that organism."
One of the largest Salmonella outbreaks in recent years occurred in the Chicago area in March, 1985. More than 16,284 confirmed case of Salmonella typhimurium were attributed to contaminated milk.
Joe Madden, deputy director of microbiology for the U.S. Food and Drug Administration's Center for Food Safety and Applied Nutrition, said the milk became contaminated after it had been pasteurized. Apparently, raw milk containing the bacteria was inadvertently mixed with the pasteurized product. Estimates state that as many as 200,000 people experienced some degree of illness from the outbreak, he said.
Another widespread problem is posed by Shigella. This pathogen can cause infections when it is transferred from infected humans onto food or to another person. It is also considered a water-borne bacteria.
In 1987, there were 23,860 cases of shigellosis, according to the CDC. Once again, the number of illness is believed to be substantially under-reported.
The contaminant was also responsible for a recent large outbreak. This particular episode demonstrated how new food processing techniques can present additional risks.
Shredded lettuce was identified as the source of 347 confirmed cases of shigellosis in the Texas area of Midland-Odessa in the fall of 1986. Apparently, the lettuce was processed at a central plant and then distributed to a number of restaurants. One of the workers shredding the lettuce was later diagnosed as having shigellosis, said the FDA's Madden.
Significant Bacterial Threat
"This is a new food processing technique, you might say, or at least the centralization of processing," he said.
Shigella's symptoms are similar to salmonellosis, but can also include bloody diarrhea.
Camphylobacter is another significant bacterial threat, said health officials. There were 10,021 reported cases of Camphylobacter in 1987, but the CDC estimates that the actual figure was as high as 2,100,000.
"The number of reported cases reflects only a small proportion of the total illness due to Camphylobacter in the United States," said the CDC's William C. Levine.
Several reasons account for the lack of more accurate numbers, he said.
"People develop the illness but do not seek medical attention. Or if they seek medical attention, they are not correctly diagnosed. Or when they are cultured for the infection then there is a false negative. Or when they are found to have Camphylobacter then the illness is not reported to the state or the CDC," he said.
Symptoms for Camphylobacter are similar to shigellosis.
Another microorganism that's posing an increasing number of problems is Listeria.
Although there are about 1,700 confirmed case of the Listeriosis per year, about 26% of these result in fatalities. The largest such outbreak occurred in Los Angeles County in 1985 when a contaminated Mexican-style soft cheese caused more than 142 illness, including 48 deaths. Most of the deaths were stillborns or neonatals, considered a high risk group for food-borne illnesses.
"We find that certain foodstuffs are notoriously contaminated with Listeria. This is one of the biggest surprises with food," said Los Angeles County's Fannin. "I wonder if we couldn't eliminate neonatal deaths by ferreting out Listeria and getting rid of it."