The use of an antibiotic to treat cattle is accelerating the spread of resistant strains of human stomach bugs, according to a new risk assessment.
Les Crawford and colleagues at the Georgetown Centre for Food and Nutrition Policy in Washington DC have warned that there could be serious public health implications in injecting animals with fluoroquinolone.
Their quantitative risk assessment, published in the latest issue of the journal Food Control , projects that this might lead to the majority of beef cattle infections of Camplyobacter jejuni - the most commonly identifiable cause of human enteritis and diarrhoeal disease - being untreatable by the antibiotic within a decade.
"The worst-case scenario is that the percentage of campylobacter organisms that are resistant to fluoroquinolone will increase each year in the United States in beef cattle, reaching between 50 and 84 per cent of the organisms after ten years," Crawford said.
Campylobacter infections are almost always transmitted to people through beef or chicken that has not been properly cooked.
Most sufferers make a full recovery, but a small percentage develop more serious conditions that can be fatal.
Such cases are usually treatable with fluoroquinolone, an antibiotic that is also used against many other human bacterial infections.
Crawford's risk assessment drew on data from a variety of scientific literature, looking at estimates of the quantity of campylobacter in specific types of beef; assessments of consumer behaviour in handling and cooking meat; estimates of the potential exposure of individuals to the bacteria and the likely outcome of the resultant illness.
A second model was then created to study the spread of fluoroquinolone-resistant campylobacter.
Before the antibiotic was approved for cattle in the US in 1998, the proportion of resistant campylobacter in the human population was calculated to be 1.3 per cent.
Two years later, Crawford said it had risen to 3 per cent. In the United Kingdom, where it was introduced as a treatment for cattle in 1993, the level was 12 per cent after three years.
"We recognise that the primary source of increasing resistance is in human medicine, but it is also clear that veterinary medical uses can contribute to overall resistance patterns," Crawford said.
"My feeling is that we should not use antibiotics in animal foods that have essential implications for human therapy."