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for National Geographic News
August 7, 2006
The bacteria that cause a common food-borne illness show low drug resistance in Australia, unlike similar strains from the United States and Europe, a study has found.
Scientists behind the finding say Australia’s de facto ban on certain antibiotics in poultry and other livestock helps explain why.
In the study, researchers analyzed samples of Campylobacter jejuni bacteria from 585 patients in five Australian states.
Scientists found that only 2 percent of the samples were resistant to ciprofloxacin, one of the group of antibiotics known as fluoroquinolonones.
By contrast, 18 percent of Campylobacter samples in U.S. patients are immune to fluoroquinolonones, which have been used in the U.S. to prevent or treat respiratory disease in poultry for a decade.
The study, led by Leanne Unicomb, a graduate student at Australian National University in Canberra, was published in the May issue of the journal Clinical Infectious Diseases.
“The findings add to the growing body of evidence suggestive of the problems [of] using fluoroquinolonones in food-producing animals,” Unicomb wrote in an email.
Campylobacter is the most common food-borne disease in the U.S. and many other industrialized countries.
People can contract the pathogen by consuming undercooked poultry or meat, raw milk, or contaminated water.
Symptoms include fever, vomiting, and diarrhea. In rare cases, the disease can trigger paralysis or death.
“In most industrial countries Campylobacter is more commonly reported than Salmonella, a better-known cause of food poisoning,” Unicomb said.
“The number of cases of Campylobacter have been on the rise [in Australia] since the early ’90s.”
In the U.S., about 1.4 million people contracted Campylobacter infections last year, according to the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia.
While the infection rate in the U.S. has dropped over the last decade, the bacteria have grown more drug resistant.
According to the CDC, surveys between 1986 and 1990 found no signs of resistance to the antibiotics in U.S. Campylobacter infections.
But by 1997 strains resistant to the antibiotics accounted for 12 percent of human cases. In 2001 the figure climbed to 18 percent.
Public health experts say many factors contribute to Campylobacter’s drug resistance, among them the widespread use of fluoroquinolonones by U.S. poultry farmers over the past decade.
Fluoroquinolones were first approved for use in humans by the U.S. Food and Drug Administration (FDA) in 1986.
In 1995 the FDA granted poultry farmers permission to the use the drugs in livestock.
Last year the FDA banned the antibiotic from food-producing animals, citing the concerns raised by public health experts over drug-resistant bacteria.
Frederick Angulo, an epidemiologist with the CDC, monitors the drug resistance of food-borne pathogens in the U.S. food supply.
“The people who are most likely to get infected with food-borne diseases include the most vulnerable people in the population”infants and young children and also the elderly,” he said.
He says that Campylobacter infections are entirely preventable, as is the bacteria’s antibiotic resistance.
“In many ways what’s occurring with Campylobacter is an indicator for a broader issue, which is Ôæñ antibiotic-resistant bacteria in the food supply,” he said.
Peter Collignon of Canberra Hospital in Australia is an expert on drug-resistant pathogens.
In a letter published late last year in the journal Emerging Infectious Diseases, he said agricultural use of fluoroquinolonones spurred “rapidly increasing resistance rates in most countries.”
“In the United States, 19 percent of Campylobacter [specimens isolated in] humans are now [antibiotic] resistant, and resistance rates greater than 80 percent are seen in Spain,” he wrote.
“By contrast, in Australia, where fluoroquinolones were never approved for use in food animals, domestically acquired infections with fluoroquinolone-resistant Campylobacter are rarely found in humans.”
Unicomb, the author of the current study, says the low drug-resistance rate of Campylobacter in Australia matches that of Norway and Sweden, which have either never approved or banned the drug from use in livestock.
“By contrast, countries that permit the use of fluoroquinolones in animals detect ciprofloxacin resistance in 10 percent or more [cases],” she said.