In that light, two recent pieces about the role of agriculture in the rise of antibiotic resistance are interesting. The New York Times described a new study in the Journal of Occupational and Environmental Medicine ("Persistence of livestock-associated antibiotic-resistant Staphylococcus aureus among industrial hog operation workers in North Carolina over 14 days," Nadimpalli et al.)
that reports that workers at industrial hog farms can carry antibiotic-resistant bacteria, Staphylococcus aureus, in their nostrils for up to four days.
Twenty-two workers provided 327 samples. S. aureus carriage end points did not change with time away from work (mean 49 h; range greater than 0-96 h). Ten workers were persistent and six were intermittent carriers of livestock-associated S. aureus. Six workers were persistent and three intermittent carriers of livestock-associated multidrug-resistant S. aureus. One worker persistently carried livestock-associated methicillin-resistant S. aureus. Six workers were non-carriers of livestock-associated S. aureus. Eighty-two per cent of livestock-associated S. aureus demonstrated resistance to tetracycline. A majority of livestock-associated S. aureus isolates (n=169) were CC398 (68%) while 31% were CC9. No CC398 and one CC9 isolate was detected among scn-positive isolates.As the NYT piece notes, eight-six percent of this sample of hog farm workers carried bacteria for at least 24 hours, compared with about one-third of the non-farm worker population.
This is a problem because the resistant variety of S. aureus, MRSA, has made its way into hospitals and is responsible for thousands of deaths. Further, many people believe that industrial farming is the cause of much of the antibiotic resistance that is now becoming such a problem, because animals are fed antibiotics to speed their growth, and many of those antibiotics are used to treat human diseases. Indeed, the majority of the antibiotics used in the industrialized world are given to animals. When bacteria on the farm become resistant to antibiotics, as this study shows, they don't necessarily stay on the farm. How they spread has been difficult to document, but might include consumption of contaminated meat, and Nadimpalli et al. report another pathway.
|Hog farm; Wikipedia|
But much of this is controversial. Is agricultural use of antibiotics in fact to blame for the problem, or is it overuse of antibiotics by the medical system? Indeed, there's less of a problem in, say, Scandinavian countries where for decades physicians have prescribed antibiotics at a much lower rate than they have done in the US. Do resistant bacteria really spread in considerable numbers from farm to city? This may be less controversial with the publication of the Nadimpalli et al. paper, but critics will say that the sample size was small and anyway, documenting a mechanism doesn't mean this is what has happened.
We all tend to pick and choose facts to support our convictions. Indeed, if you look at how scientists, in any field, cling to their explanations, 'convictions' is perhaps a muted term for what is being clung to. How we think about these questions may well reflect what we believe more generally about the food system, how or even whether animals should be farmed for meat, whether we patronize farmers' markets rather than industrially produced food, and so forth rather than what we, or anyone, actually know about the causes of antibiotic resistance. That is, our personal sociopolitical positions seem clearly be correlated with, if not strongly influencing, our scientific position.
Yesterday, an opinion piece by Iowa veterinarian and pig farmer Howard Hill appeared in our local paper, and in papers around the country. Hill believes that farmers are being unfairly blamed for antibiotic resistance in humans.
...the claim that "70 to 80 percent of all antibiotics sold in the United States each year are used in livestock" is a straw man. More than a third of those drugs aren't used in human medicine, another third are not considered highly important to human medicine, and most of them aren't used for growth promotion. Critics also ignore the fact that there are a lot more cows, pigs and chickens than people. In 2011, for example, 30 million pounds of antibiotics were sold for use in more than 3 billion livestock and poultry, compared with 7 million pounds for 311 million people, meaning each person used nearly five times more antibiotics than were used in each food animal.Is he making selective use of the data? Yes, but isn't everyone who talks about this issue? And does that make our assertions wrong? Doesn't prior belief influence our understanding of what the data show?
While Rome burns
President Obama yesterday issued an executive order aimed at combating antibiotic resistance. The order accepts that industrial agriculture may have a role in increasing resistance, but it adds little to the FDA order of several months ago:
The Food and Drug Administration (FDA) in HHS, in coordination with the Department of Agriculture (USDA), shall continue taking steps to eliminate the use of medically important classes of antibiotics for growth promotion purposes in food-producing animals.Not many teeth here. Years ago Europe took much the same approach, requiring that the use of antibiotics for growth promotion be reduced, but a lot of reclassification of antibiotic use for medical purposes followed, as many expected in the US following the FDA announcement last December, which we blogged about here, and again with this Executive Order.
Again in Scandinavia, the use of antibiotics for growth promotion has been banned, beginning in Sweden in 1986, but farmers have not suffered. According to a piece in the BCMJ in 2011:
In 1986, Sweden became the first country to regulate the withdrawal of antibiotics used in food animal production. By 2009, Swedish sales of antibiotics for use in agriculture were reduced from an average of 45 tons of active substance to 15 tons. Sweden was followed by Denmark, the United Kingdom, and the Netherlands.
Danish swine and poultry production continued to flourish with gradual reductions of antibiotic use beginning in 1992 and continuing to 2008 (latest data). During this time, Danish farmers increased swine production by 47% while reducing antimicrobial use by 51%. As well, poultry production increased slightly while reducing antimicrobial use by 90%. Denmark remains one of the largest pork exporters in the world.So, whether or not growth promoting antibiotic use in animals is a major cause of resistance is not really an issue, and we needn't even continue to have the discussion. If there is any chance it is, why not ban it entirely? Experience in Scandinavia suggests there won't be dire economic consequences -- unless you're a pharmaceutical company making antibiotics for animals.
Faith in science
We have often written here about the economic interests that drive the course of Big Science. Can we have faith in science if there is considerable faith in science? People are, after all, only human, and people of all faiths, including science, defend their faiths. Further, it's often impossible to disentangle belief from vested interest. If you've got a hammer, or a hammer to sell, everything looks like a nail.