Microbiological Threats Lurking in Food
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.”
The federal government has intensified its monitoring of processed foods for Listeria contamination and has proposed a number of preventive measures for the food industry as a result.
Potentially Fatal Illness
An organism that is more familiar to the public, although its incidence is rare, is Clostridium botulinum. The toxin’s spores cause botulism, a severe illness that can be fatal.
A recent episode of botulism, however, surprised FDA officials. A commercial version of chopped garlic in oil was the cause of three illnesses in the New York City area recently.
“That hit us out of the blue,” said Douglas Archer, FDA’s microbiology director. “The reason is that (scientific) literature told us that botulinum spores cannot grow in garlic . . . But these organisms adapt if given enough time.”
There were extenuating circumstances in the garlic oil episode. Namely, the victims left the product at room temperature despite a statement on the label about keeping the oil refrigerated. As a result, FDA has ordered all firms manufacturing similar items to place refrigeration warnings in prominent label positions and to increase the acidity of the items.
Botulinum spores can be destroyed through proper heating above 175 degrees F, Archer said.
One common toxin, Staphylococus, is not killed by heating, however. Last month, the FDA ordered a recall for institutional-sized cans of mushrooms because of suspected Staphylococcal contamination. The canned mushrooms, manufactured in the People’s Republic of China, were linked to 79 illnesses.
Staphylococcal food poisonings are characterized by rapid and sometimes violent onset of nausea, cramps, vomiting and occasional diarrhea, said the FDA.
Although Staphylococus is considered one of the more common food-borne bacteria, there are no national figures kept on the number of reported cases because of the difficulty in diagnosing it, said the CDC’s Levine.
Viruses are another category of pathogens that can cause severe illness.
Hepatitis Type A infections are traced to both food and water. The contamination occurs as a result of contact with humans who are infected with the virus. Infected individuals can also spread the illness to others through contact.
The CDC reports that there were 25,280 cases of Hepatitis Type A in 1987, but is not able to establish how many of these were food-related.
Fannin said that Los Angeles County officials have seen a number of hepatitis cases recently in people who have returned from travel to Asia.
There are other pathogens-- Vibrio vulnificus, Norwalk virus, Yersinia, E. Coli-- that are also troubling health officials and food producers around the country. But whatever the problems posed by these and other contaminants, the consensus remains that food is safe to eat.
“In Los Angeles County we have more than 21 million commercial meals served in a week. The few number of food-borne outbreaks that we get has to indicate that we have a safe food supply,” said Fannin. “With reasonable hygiene measures we could eliminate half of what we do experience or more.”
