by Audrey Hingley
When it comes to food poisoning, big outbreaks make headlines. E. coli in apple juice and alfalfa sprouts. Listeria in cheese and hot dogs. Salmonella in eggs and on poultry. But the most frequently diagnosed food-borne bacterium rarely makes the news. The name of the unsung bug? Campylobacter.
"Most Campylobacter infections are sporadic and not associated with an outbreak, but we know it causes up to 4 million human infections a year," says Frederick J. Angulo, D.V.M., an epidemiologist with the national Centers for Disease Control and Prevention.
Federal and state health experts have long recognized that Campylobacter causes disease in animals. Conclusive proof that the bacteria also causes human disease emerged in the 1970s, and by 1996, Campylobacter was sitting atop the bacterial heap as the number one cause of all domestic food-borne illness. (See "Tracking Down Trouble: Bacteria That Cause Food-Borne Illness.")
In addition, with the emergence of antibiotic-resistant Campylobacter, "the true magnitude of the problem is becoming clearer," says Angulo, who also heads the CDC arm of the National Antimicrobial Resistance Monitoring System.
Campylobacter is commonly found in the intestinal tracts of people or animals without causing any symptoms of illness. But eating contaminated or undercooked poultry or meat, or drinking raw milk or contaminated water, may cause Campylobacter infection, or campylobacteriosis.
Symptoms of campylobacteriosis usually occur within two to 10 days of ingesting the bacteria. Children, the elderly, and people with weakened immune systems are particularly at risk. The most common symptoms include mild to severe diarrhea, fever, nausea, vomiting, and abdominal pain.
Most people infected with Campylobacter can get well on their own without treatment, though antibiotics may be prescribed for severe cases. But complications can occur, such as urinary tract infections or meningitis. The bacteria also is now recognized as a major contributing factor to Guillain-Barré syndrome, the most common cause of acute paralysis in both children and adults.
Concerns About Chicken
Although found in many farm animals, Campylobacter in poultry is causing experts the most concern. There have been several studies pointing to high levels of Campylobacter present on poultry at the retail level, including a recent two-year Minnesota Department of Health study that found that 88 percent of poultry sampled from local supermarkets tested positive for the bacteria.
"The retail study was in collaboration with the Minnesota Department of Agriculture; their inspectors went to supermarkets throughout the St. Paul/Minneapolis Twin Cities area to cover a variety of supermarket types, from big chains to mom-and-pop stores," says Kirk E. Smith, D.V.M., a Minnesota state epidemiologist who participated in the study.
Many prior surveys have found Campylobacter contamination rates of between 40 and 60 percent, he says. "But 88 percent--this degree [of contamination] surprised even me," he admits.
In studies conducted by the U.S. Department of Agriculture's poultry microbiological safety research unit, more than 90 percent of poultry tested positive for Campylobacter, in levels ranging from one cell to over a million cells per bird.
Norman J. Stern, Ph.D., research leader for the unit, says the infection of poultry broiler flocks typically occurs at week three in the six-week growing cycle. It's not unusual, he says, for Campylobacter to infect the entire flock.
Things only get worse by the time the chickens reach the processing plant, he says. USDA studies have found a hundredfold increase in bacteria amounts on the birds' exterior from that detected on the farm. "The exterior contamination represents consumer exposure," he explains.
To help reduce that exposure, Stern says the poultry industry is currently participating in a USDA-led study that will cover "every element of production where chickens can become infected, from ... shells to farmers' boots to wild bird droppings. When we're done … we will be able to genetically fingerprint the organism so we can ascribe a relationship between various environmental sources and the spread of pathogens." The study was slated to end in September.
Resistance to Antibiotics
According to the Minnesota Department of Health study, the number of Campylobacter infections resistant to a class of antibiotics called fluoroquinolones has been on the increase since 1992. While most Americans acquired the resistant infections while on foreign travel, Kirk explains, "we have been seeing a significant increase in domestically acquired resistant cases as well." The Food and Drug Administration approved the use of fluoroquinolones in food animals in 1995. The study concluded that antibiotic use in U.S. poultry is contributing to antibiotic resistance.
Resistance to fluoroquinolones, not only by Campylobacter but by other bacteria as well, is a concern, explains Jesse Goodman, M.D., chief of the division of infectious diseases at the University of Minnesota, "because fluoroquinolones are commonly used to treat severe infectious diarrhea, often before the specific cause has been identified. Fluoroquinolones are very important drugs for treating a variety of serious human infectious diseases."
CDC studies also show an increase in resistance to fluoroquinolones and this can be correlated to fluoroquinolone use in poultry, according to Angulo. In addition, "We did a case control study in 1997, comparing people with [nonresistant] Campylobacter infections with fluoroquinolone-resistant infections, and found that those with resistant infections [were] more likely to have severe infections, bloody diarrhea, and be hospitalized."
Because of the concern over antibiotic resistance, FDA is considering whether, before it reviews a new animal drug for approval, manufacturers must assess the likelihood that use of a certain drug in food animals will transfer resistance and create a public health problem. In addition, new procedures for monitoring antibiotic use and resistance after approval also are being considered.
"FDA believes a new regulatory framework is needed to address resistance concerns raised by the food animal use of antibiotics," says Goodman, who also serves as a deputy medical director for FDA.
The Animal Health Institute, a national trade association representing manufacturers of animal health products, says it also is concerned about the possibility of antibiotic use in food animals causing resistant bacteria to develop. But the organization believes that the requirements FDA is proposing may have "unintended negative consequences on animal health ... and risk sending unhealthy animals into the food chain."
Hollinger says, "At this time we are not taking action toward withdrawal of these products from the market. We have asked the sponsors of poultry fluoroquinolone products to provide data that would describe the prevalence of resistance in poultry flocks and identify possible actions to prevent the emergence of disease in treated flocks."
Calling it a "farm to plate" approach, Hollinger says that the Campylobacter problem can be addressed "at any number of points" along the food chain. "They all need to be reviewed and evaluated for new methods to deal with the problems."
USDA's Stern says he believes the poultry industry is "trying very hard" to move toward enhanced food safety for economic as well as safety benefits. For example, he explains, a company could use extensive microbiological criteria to ensure safety as a marketing tool. Just as consumers are willing to pay more for "gourmet" coffees or specialty food items, an increasingly health-conscious consumer could be wooed by a health emphasis when it comes to safer poultry products, he says.
Vaccine on the Horizon
A team of Navy, Army, and drug industry researchers is also moving ahead in the development of a prototype vaccine for Campylobacter. The vaccine has shown promise in animal models and currently is undergoing clinical trials.
Capt. Louis A. Bourgeois, director of the enteric diseases program at the Naval Medical Research Center in Bethesda, Md., says the Navy has been involved in Campylobacter research since the early 1980s.
"Historically, the military has had longstanding diarrheal problems with troops deploying overseas," he explains. "Campylobacter was an emerging pathogen in the early '80s, and by the mid-1980s, we began doing more directed studies towards a vaccine development."
Bourgeois and his fellow researchers say an approved vaccine is likely "several years away" but they remain optimistic. Bourgeois says private companies are interested in a vaccine due to its possible application in "traveler's diarrhea," a common ailment.
"We know from animal model work that we can protect animals against Campylobacter colonization," says colleague Daniel Scott, M.D., deputy director of the Navy's enteric diseases program. "We have also gained an increasing amount of knowledge in the clinical and preclinical development of this product, especially in terms of what happens with the actual infection. We are already seeing some evidence that term protection can occur, which allows for a lot of optimism."
The Consumer's Role
While researchers, regulatory agencies, and scientists grapple with Campylobacter, what can you do to protect yourself?
"Consumers go to the supermarket thinking everything [there] is clean, and that is just not true," says Donald H. Burr, Ph.D., a research microbiologist in FDA's Center for Food Safety and Applied Nutrition. "People can't assume that anymore. Consumers have a responsibility in food safety."
Those responsibilities include prompt refrigeration, thorough cooking, avoiding cross-contamination, and washing hands and surfaces often. In addition:
Audrey Hingley is a writer in Mechanicsville, Va.
Campylobacter is not the only thing that triggers Guillain-Barré syndrome, but it is now recognized as one of the disorder's major forerunners. Guillain-Barré, which also may follow a viral illness, is an autoimmune attack on the peripheral nerves that can cause weakness and paralysis. Annually, about two people per 100,000 contract the syndrome.
"We also know that many patients who have [campylobacteriosis] seem to have a more severe form of Guillain-Barré," Leshner says.
Guillain-Barré can be difficult to diagnose in its early stages, although Leshner says clinicians often suspect anyone with "acute weakness" as having the disorder. It's usually diagnosed via clinical observation, spinal fluid analysis, and electromyogram (EMG) tests, which analyze electrical activity in muscles.
"With mild cases, probably no more is needed other than supportive care. But if the person is unable to walk or has breathing problems, more dramatic treatments may be needed," Leshner says. "A small percentage of people have residual disabilities, and these people have the form linked to Campylobacter."
--A.H.
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