Science of Resistance: Antibiotics in Agriculture
The Risk to Human Health
It is estimated that over one-half of the antibiotics in the U.S. are used in food animal production. The overuse of antimicrobials in food animal production is an under-appreciated problem. In both human and veterinary medicine, the risk of developing resistance rises each time bacteria are exposed to antimicrobials. Resistance opens the door to treatment failure for even the most common pathogens and leads to an increasing number of infections. The mounting evidence of the relationship between antimicrobial use in animal husbandry and the increase in bacterial resistance in humans has prompted several reviews of agricultural practices by scientific authorities in a number of countries, including the US.
Overview of the Relationship Between Antimicrobial Use in Food Animal Production and Antibiotic Resistance
- Exposure to antimicrobials fundamentally alters microbial ecosystems of humans, animals and the environment, which may lead to the development of antimicrobial resistance.
- Increasing antimicrobial resistance limits treatment options, raises health care costs, and increases the number, severity and duration of infections.
- Antimicrobial use is a major cause of antimicrobial resistance.
- It is estimated that, in the United States, the amount of antimicrobials administered to food animals is comparable to that used in humans. These antimicrobials are utilized largely to promote growth and prevent disease, thereby reducing production costs. A substantial amount of them are sold over-the-counter and do not require a veterinarian's prescription.
- Most food animals in the US are exposed to antimicrobials in feed, water, or by injection at some point during their lives.
- Fecal waste from food animals treated with antimicrobials, which is often composted and spread as fertilizer, is implicated in environmental contamination with resistant bacteria.
- Several lines of evidence may link antimicrobial use in food animal production to resistant infections in humans. These include: (i) direct studies tracing resistant infections in humans to specific meat and poultry operations; (ii) temporal evidence (i.e. the emergence of resistance in animal-associated bacteria prior to its emergence in human pathogens); (iii) circumstantial evidence linking human disease to trends in resistance among common bacterial pathogens such as Salmonella, Campylobacterand E. coli; (iv) studies suggesting that farmers and family members may be more likely than the general public to harbor antimicrobial-resistant intestinal bacteria; and (v) studies of the transfer of resistance in commensal bacteria.
- Most antimicrobials used in food animal production are the same as, or closely related to, drugs used in human medicine.
- Current antimicrobial use policy for animals in the US differs from policy enacted in the European Union, which has banned the use of some antimicrobials for growth promotion on the farm.
- Also of concern is the farm use of antimicrobials of critical importance in human medicine, such as fluoroquinolones and third (or higher) generation cephalosporins
- Once the prevalence of antimicrobial resistance in a population reaches a certain level, reversal of the problem becomes extremely difficult.
- The study entitled “Changes in the use of antimicrobials and the effects on productivity of swine farms in Denmark” identifies positive results from the enactment of policies in Denmark that regulate antimicrobial use in agriculture. Trends showed a decrease in antimicrobial consumption per kilogram of pig produced from 1992-2008 along with an improvement in overall swine productivity. These findings provide the best evidence supporting a ban on the use of antimicrobial growth promoters.
- For more information please see the APUA FAAIR (Facts about Antibiotics in Animals and Their Impact on Resistance) report sponsored by the Joyce Foundation. The report entitled The Need to Improve Antimicrobial Use in Agriculture: Ecological and Human Health Effects contains scientific evidence meant to inform the policy debate surrounding the use of antibiotics in food animal production. Please also see the 2005 FAAIR II report focused on obtaining improved antibiotic usage estimates in US food animal production to guide regulatory decision-making.
The U.S. Food and Drug Administration (FDA) is implementing a new strategy to encourage more appropriate and prudent use of antibiotics in food animal production. The strategy intends to curb antibiotic overuse and misuse by identifying certain antibiotics that will now require veterinary oversight via the Veterinary Feed Directive (VFD). The FDA will also help drug companies voluntarily re-label antibiotic products to remove feed efficiency and growth promotion claims. Labels will instead emphasize antibiotic use for the prevention, control, and treatment of bacterial diseases.
In July, APUA, along with multiple other national health organizations, signed a letter submitted to the FDA and the US Department of Agriculture (USDA) commenting on their proposed changes to the VFD. While the changes would keep certain over-the-counter drugs under closer supervision by veterinarians, they would alter the definition of the veterinary client patient relationship (VCPR) in a way that allows a veterinarian’s practice to issue a VFD without requiring a visit to each facility. The letter states support for the FDA and USDA to retain the current, stricter VCPR definition.