Superbugs, Agricultural Antibiotics, and Farm-Worker Infections: A New Study Connects the Dots
Infections caused by antibiotic-resistant bacteria—so-called "superbugs," such as methicillin-resistant Staphylococcus aureus (MRSA)—are on the rise and grabbing headlines globally. Indeed, the World Health Organization considers them to be one of the "three greatest threats to human health."
Increasingly, experts are blaming this rise in resistance in large part on the widespread practice of giving subtherapeutic doses of antibiotics to otherwise healthy livestock, in order to promote weight gain. Earlier this year, Rear Admiral Ali Kahn of the Centers for Disease Control testified before Congress that "there is unequivocal evidence of the relationship between [the] use of antibiotics in animals and [the] transmission of antibiotic-resistant bacteria causing adverse effects in humans."
Last month, for the first time, the Food and Drug Administration released data on the quantity of antibiotics distributed to animals in the United States, and the numbers were shocking—an incredible 28.8 million pounds, compared to just seven million pounds prescribed to humans, with more tetracycline produced for animal use each year than the combined weight of all the antibiotics manufactured for human consumption.
Continuing to join the dots, earlier today a team from the University of Iowa published the results of a study [PDF] showing that 3.7 percent of farm workers have been diagnosed by a doctor with an MRSA-related infection. Writing in Wired, Maryn McKenna, author of a recent book on the subject of MRSA, Superbug, puts the finding in context:
So what does this tell us? It’s a beginning. It makes clear that MRSA is occurring among farm workers, probably more than in the general population, and it spotlights some ways in which they are being made more vulnerable to infection from animals or from each other.
The researchers themselves are careful to note that their 3.7 percent finding may well be an underestimate, since the study relied on self-reports and only achieved a low response rate overall. What's more, they add
Pork producers may not seek medical treatment, or infections may be misdiagnosed by rural physicians. Some producers may not want to disclose MRSA infections in workers or pigs due to fear of identification.
As McKenna and the researchers conclude, much more work is needed to understand the ways in which livestock-associated MRSA and human infection are related.
In the European Union, where farmers have been banned from administering antibiotics used to treat humans to their livestock since 1998, there has been a significant reduction in the numbers of antibiotic resistant bacteria found in both animals and food.
In the United States, livestock and poultry producers, pharmaceutical companies, and the American Veterinary Medical Association have thus far successfully opposed similar legislation. But you can expect the issue to come up again later this year, when the Trans-Atlantic Task Force on Antimicrobial Resistance, established by Obama in November 2009, presents its recommendations. In the meantime, this study goes some way to filling in the data gap, and providing a fuller picture of the threat that the agricultural overuse of antibiotics poses to public health.
Photo of cutaneous abscess on hand caused by MRSA, taken by Gregory Moran, M.D., for the CDC.