In the call for reducing farm antibiotic use, let's make sure we're comparing apples to oranges
When the U.S. Centers for Disease Control announced its annual Get Smart About Anbitiotics Week earlier this month, to remind people to use antibiotics intelligently in order to avoid losing the effectiveness of these important medicines, it brought out media reports citing a statistic so commonly used as to now be widely accepted as fact: " Over 70 percent of antibiotics go to livestock, not to people," quoted health reporter Martha Rosenberg, as example. Most commonly, media and Internet pundits repeat the statistic that anywhere from 70 percent to 84 percent of all antibiotics used yearly in this country go to food animals. Let's take a deeper look at those figures:
Although antibiotic availability is strictly regulated by the U.S. Food & Drug Administration, the reality is that the amount of the drugs actually used is not publicly known. Ironically, although now FDA carefully tracks and reports a summary each year of the tonnage farmers use, a similar figure for the amount used in humans is not. Even reliable estimates of the amount of antibiotics people use are decades old. The percentages commonly cited by news media are similarly only suspect estimates, not only because they rely on those old estimates of human use, but also because they rely on estimates of farm animal use based on numerous unproven assumptions, several of which are clearly wrong (like the fact it creates out of thin air tonnages for two drugs that although they were FDA-approved were never sold in the United States.)
Even if you're willing to accept the 70 percent to 84 percent figures at face value, it's important to ask whether the statistic is even relevent. Here’s how to put the numbers into perspective for your customers:
- Each year, America’s farms grow one third more animals and birds than the combined human population of the entire world. Those 9.5 billion birds and animals outnumber the U.S. human population by more than 31 times. Shouldn’t their antibiotic use be higher?
- In addition, farm antibiotics?—?like most medicines, whether animal and human?—?are given to animals according to their weight. So you can only meaningfully compare the relative use between animals and people on a pound-per-pound basis. Not only does the U.S. population of farm animals outnumber humans, it also outweighs the U.S. human population?—?by almost 3.4 times. Again, since dose is based on weight, we should naturally expect animals to consume more antibiotics. In this case, their share of the total strictly by weight should be 77 percent.
- Rather than hogging all the antibiotics, farm animals on a pound-per-pound basis actually use only a fraction of the antibiotics humans do. Based on one estimate by a USDA veterinary researcher, pound-for-pound, each human and pet consumes 10 times more of the nation’s supply of antibiotics than each farm animal uses.
- Opponents of farm medications use another statistical sleight of hand to further inflate the implied risk that farm antibiotic consumption might be contributing to antibiotic resistance. Not every type of antibiotic they loop into their calculations is relevent to the resistance debate. Several antibiotic classes?—?those known as ionophores, bambermycin, carbadox, tiamulin and arsenicals?—?are never used in humans. So, their use in farm animals poses no risk of causing human antibiotics to fail. Subtract the drug manufacturers’ own estimates for how much of those antibiotics are used from the inflated statistics, and the oft-repeated 70 percent figure immediately falls to only 58 percent.
- Finally, when you recalculate the estimated use of antibiotics by converting the dosage for farm animals into a comparable human dose?—?what’s known as an “allometric calculation,” which comes as close as possible to making an apples-to-apples comparison between the dose given humans and the dose given animals?—?it grows clear that farm use is not out of line. Depending on which allometric model you use, farm animals should be consuming from 2.1 to 3.7 times more antibiotics than humans in order to receive a comporable dose. In other words, an appropriate share for farms, based on the best numbers we have, should fall between 70 percent and 79 percent.