New Bugs on the Block
May 1995 - New Technologies

By: Lynn A. Kuntz
Associate Editor*

*Editor since August 1996

  Mother Nature seems to take perverse pleasure in finding ways to sicken the human populace. One of the most insidious means is via food-borne pathogens. Despite the best efforts by the food industry, it seems like one wrong move can send hundreds to the hospital.

  Some bacteria have emerged as new sources for concern. Others are familiar enemies, but even these can take the food industry by surprise. Since food safety is literally a case of life and death, it is a critical concern to the food industry.

New cases

  If the headlines are any indication, the incidence and severity of food-borne illness appear to be on the rise. Certainly the reported cases have risen. However, these only make up a small proportion, estimated to range from 1% to 10%, of the actual incidents. Current estimates place the number in this country as high as 8 million cases per year, resulting in up to 7,000 deaths. The USDA's Department of Economic Research and The Centers for Disease Control (CDC) estimate that food-borne illnesses cost this country between $5.6 billion and $9.4 billion in 1993, including medical expenses, productivity losses, industry costs such as recalls, and investigative and monitoring processes.

  "Consumers are more aware that bacteria can contaminate foods and cause illness," says Payton Pruett, Ph.D., chief microbiologist, Webb Technical Group, Raleigh, NC. "They are more apt to seek medical treatment. Epidemiological techniques have improved. There are better techniques for tracking these illnesses down, and there are better laboratory techniques. If you see a trend of increasing reports of foodborne illness, it could be attributed to those reasons, but it is hard to say with any certainty because the cases are vastly under-reported."

  If the growing numbers do indeed reflect an increase in incidents, it would come as no surprise to the experts.

  "Many believe we're seeing an increase in food-borne illness," observes Joseph Madden, Ph.D., strategic manager for microbiology, CFSAN/FDA, Washington, DC. "You can identify a number of factors. There are more prepared and ready-to-eat foods. Some people are saying that individuals in the home and in foodservice are getting sloppy with food preparation and hygiene, plus we are seeing what we are calling emerging pathogens."

New faces

  No one questions that more organisms have been linked to outbreaks. Twenty-five years ago, the food pathogens most frequently blamed for illness included Clostridium perfringens, Salmonella and Staphylococcus aureus. Clostridium botulinum also received a great deal of attention, not because of frequency, but because of its deadly consequences.

  These days the list of common food pathogens includes Campylobacter jejuni, Escherichia coli 0157:H7 and Listeria monocytogenes. Several other organisms have not yet caused any major outbreaks in this country, but pose a threat, such as Yersina enterocolitica, Shigella and several Vibrio species including V. cholera.

  The perception is that many of these are "new" organisms but, with the possible exception of E. coli 0157:H7, most have been identified as potential food-borne pathogens for years. Scientists initially believed that some, such as Listeria, only affected animals. However, sporadic outbreaks in the 80s, culminating with the Jellisco cheese outbreak, established Listeria as a major human health risk.

  Other organisms adapted to new niches. For example, Salmonella enteritidis appears to have adapted to infect chicken ovaries and can show up in the yolk membranes of eggs. Some researchers believe that through mutations or genetic changes, some organisms have acquired the ability to infect humans.

  "The first real food-borne outbreak of E. coli 0157:H7 was in 1982," says Madden. "The CDC looked at its culture collection and the first 0157:H7 they had was dated 1978. That microorganism did evolve, and it's continuing to change. The apple cider outbreak in New England occurred in acidic product. Apparently, this microbe has adapted to be acid tolerant. The last U.S. outbreak occurred in California and Washington in salami. That strain of E. coli is more acid tolerant than the one we had in New England. That creates big problems, since acid is one of the control mechanisms used to keep microbes at bay."

  Many also believed C. jejuni was restricted to animals. However, it now appears that Campylobacter causes more illness than Salmonella and Shigella combined. It grows under fairly restrictive conditions and is fragile and difficult to culture, so until recently it was difficult to establish it as the causative agent. Although Campylobacter is prevalent, especially in animal products, its sensitivity to temperature, oxygen, lack of moisture and competing organisms make it easy to control with good sanitation and handling practices.

  Many of the emerging pathogens exhibit a particularly worrisome trait: low infectious doses. In the past, depending on the organism, it usually took a very high microbial load to create an infection. Scientists attributed the recent E. coli infections from undercooked hamburger in the West to product with 10 organisms or less. Campylobacter infections can occur with counts in the hundreds.

  "We seem to see that occurring with Salmonella enteritidis; it doesn't take much to cause illness," notes Madden. "The figures that we used to have for Vibrio cholera and Salmonella indicated that you had to ingest large numbers, tens or hundreds of thousands to cause illness. These organisms appear to be adapting to create lower infectious loads."

  Additionally, the effects can be more severe than previously encountered. Along with the usual enteric illnesses and their symptoms, many more serious problems result. For example, E. coli 0157:H7 may cause hemolytic uremic syndrome, which can result in acute kidney failure in children and may damage the central nervous system. Listeria often causes meningitis and promotes abortions. Even Salmonella, once thought only to make you wish you were dead, can kill - especially the young, the elderly and the immune compromised.

  Are the organisms more deadly, or have we become more susceptible to their effects?

  "Being too clean, or 'oversanitation' has been implicated in some quarters," says Pruett. "We used to expose ourselves to dirtier environments and to low levels of some of these harmful organisms. That's not happening as much. We may not be letting our immune systems adapt or build up resistance to these organisms, so the severity of our reactions could be increasing."

  Another challenge to previous assumptions is that some organisms possess the ability to grow at refrigerated temperatures. Both Listeria and Yersinia thrive at temperatures near the freezing point. This signals potential for problems in prepared, chilled foods.

New places

  While much of the recent focus has been directed toward meat, poultry and dairy products, these are not the only products at risk. Most food pathogens tend to inhibit the digestive tracts of animals, but some of these organisms are ubiquitous. Many, including Vibrio and Campylobacter, contaminate water. Vegetables can harbor unfriendly organisms; L. monocytogenes-contaminated cabbage was responsible for an outbreak in Canada, and researchers found C. jejuni on mushrooms.

  "Many microorganisms, like E. coli, are associated with livestock, so there's residue in the manure," points out Julie Albrecht, Ph.D., extension food specialist, University of Nebraska, Lincoln. "Manure is always going to be higher in microbial content, whether or not it contains pathogens. If that manure is used as a fertilizer by people working with organic farming or sustainable agriculture, it can come into contact with the crops. That's fine, but it's a change in a practice and we haven't changed our handling of the foods."

  Changing practices provide fodder for a number of theories. How has mechanization affected the microbial load? Has intensive animal farming or the use of antibiotics somehow changed the balance?

  "We slaughter spent dairy cows for hamburger. Is more of that going into the industry?" asks Albrecht. "When an animal is around for 10 years, it has a longer time to establish different microflora in its tract."

  Bacteria also show a propensity for popping up in unexpected places. In the last 20 to 30 years, most botulism has occurred in home-canning situations. Several foodservice outbreaks occurred, but not in canning. In New Mexico, C. botulinum grew in baked potatoes held at room temperature. In Illinois, toxin formed when contaminated cooked onions were piled on a stove for an extended period. These would not normally be considered anaerobic conditions, but apparently they turned out to be just that. A commercial product, chopped garlic in oil, supported C. botulinum growth when stored at room temperature. Normally, garlic produces a bacteriocidal effect.

  "One thing that scares us is home vacuum packaging," warns CFSAN/FDA's Madden. "If you pull the air out of something and create a vacuum, you've got the possibility of botulism. This method is used in some delis and, frankly, those delis are not operating under Good Manufacturing Practices. We're trying to control that now - make certain they label shelf life, etc."

Changing paces

  While these situations may cause problems, it seems that the biggest culprits are poor sanitation and handling practices. Industry has a fairly good track record, but when there is a lapse, the consequences can be far-reaching. Wider distribution and large-scale operations can mean that instead of localized, limited outbreaks, you can affect tens of thousands of customers.

  Mishandling occurs frequently on a smaller scale, both in foodservice operations and in the home. It's the "don't use the same cutting board, cook and cool properly, wash your hands" refrain. Madden cites a study on meat slicers in delicatessens that found five out of 12 had Listeria on their blades.

  "I think there's some confusion as to where these illnesses are actually generated," says Pruett. "Usually the processor is not to blame; it's the handling after the product leaves the plant - such as in foodservice establishments and in homes - that leads to food-borne illness. That's something that's important to convey to the consuming public."

  Everyone agrees that better communication of the correct procedures is critical. But we have to realize that, with foodservice at least, this communication would be coming from the same work force that seems to be having problems in preparing food consistently.

  "We must learn to communicate so that everyone understands the science," says Albrecht. "We're a sophisticated society. Most of us can understand computers or some kind of electronic gadgets, so I think it's possible. But we've made such technological strides in so many areas that sometimes simplistic things like refrigerating food seem to be an old-fashioned concept."

  Currently the onus is on the food industry to minimize the risk. While modern processes cannot guarantee 100% sterility for the entire food supply under all conditions, HACCP programs are believed to bring the industry as close to this as practically possible. To this end, the Food Safety Inspection Service is proposing that, along with an inspection process, meat processors establish HACCP plans that identify the points critical to preventing microbial hazards and closely monitor these.

  Although this proposal would be mandatory for the meat industry, the rest of the food industry hopes to be able to implement HACCP for other products. It is certainly a much more reasonable answer than increased product testing. Along with increased cost, relying exclusively on microbiological testing can give a false sense of security, especially since such low levels of organisms can be responsible for an outbreak.

  "You shouldn't have to test everything that comes out of a plant," points out Pruett. "HACCP says if you control your processes within certain limits, you can be almost 100% sure that the product that comes out will be safe. That doesn't mean it eliminates end product testing - it needs to be done at specified intervals to verify a HACCP process - but excessive product testing is not the answer. HACCP, if done correctly, if it is not overwhelming, and if it is drawn out as simply as possible, can effectively control these problems."

  As the industry searches for more effective means to control these pathogens, we can be certain that Mother Nature is finding ways to confound our efforts. The challenge is to try to keep up and, if possible, stay one step ahead.

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