August 18, 2010

A MRSA Story: The FDA, CAFOs, and Antibiotic Resistant Bacteria

In June, the Food and Drug Administration issued Draft Guidance on the Judicious Use of Medically Important Antimicrobials in Food-Producing Animals. The FDA recognizes in the guidance that the “overall weight of evidence available… supports the conclusion that using medically important antimicrobial drugs for production or growth enhancing purposes… in food-producing animals is not in the interest of protecting and promoting the public health.” The public health concern arises where bacteria in these animals develop resistance to the drugs and then are transmitted to food workers and consumers, who then introduce the drug-resistant bacteria into their communities. 

In a new book, Superbug: The Fatal Menace of MRSA, journalist Maryn McKenna details the emergence of one of the most common and increasingly prevalent drug-resistant bacteria, methicillin-resistant Staphylococcus aureus (MRSA). While MRSA was once primarily found in hospitals, McKenna traces the emergence of community-based strains of the bug that evolved independently to also cause serious infections in people with no connection to the hospital or other traditional environments with MRSA. Her book also examines the ability of MRSA to use domestic pets as hosts and then infect their human owners, as well as the impact of antibiotic use in the food production sector (there's a great book interview from Fresh Air).

MRSA is part of the Staphylococcus genus, which includes a variety of ancient bacteria that are, as McKenna says, “probably one of mankind’s oldest evolutionary companions.” Staphylococcus aureus, or S. aureus, is mostly benign and at any given moment is present in nearly one-third of the population. Humans and our bacteria live in an intimate balance, but when that balance with S. aureus is toppled, the bacteria may turn extremely virulent and even deadly. S. aureus can attack the human body with rapid and devastating consequences, ranging from simple skin abscesses to muscle and bone infections, toxic shock, and pneumonia. 

Bacterial infections are commonly resolved with antibiotics, but over the past 70 years since the introduction of penicillin, these bacteria have evolved increasing resistance to even the most infrequently used drugs. According to the FDA, the development of antibiotic resistant bacteria—including MRSA—is a mounting public health problem of global significance. While once mostly found in hospitals and health-care settings, MRSA has emerged in the community as strands that are wholly unrelated to their hospital counterparts and unique in their resistance properties. 

The spread of resistant bacteria is due to many factors, including the pervasive use of antibacterial drugs in humans and animals. In animals, these drugs are used in concentrated animal feeding operations (CAFOs), enormous facilities that raise threshold numbers of cows or pigs, for their intended purpose as well as “subtherapeutic” or “nontherapeutic” uses: increasing the rate of weight gain or improving feed efficiency. Unlike the use of these drugs for the treatment, control, or prevention of disease, these subtherapeutic uses are expressly directed at enhancing the production of animal-derived products. After developing resistance in the animals, MRSA lingers in manure lagoons and can be spread by flies and even the wind. McKenna notes that, in the Chesapeake Bay, researchers have found resistant bacteria carried long distances by flies. 

In Superbug, McKenna details the discovery of a pig strain of MRSA in a six-month old baby in the Netherlands, whose father—a pig farmer—transmitted the bacteria to her, and of a similar strain in Canadian pigs. This is startling not only because it raises the likelihood that animals can be a reservoir of MRSA that can infect humans (animal-to-human transmission), but it also demonstrates the ability of MRSA to spread rapidly and internationally, from Europe to North America in a short amount of time. While the humans infected with the pig strain of MRSA were asymptomatic, the uncertainty of what may happen when a critical human mass is infected, or when the pig strain merges with other antibiotic resistant strains, warrants precautionary measures. 

FDA’s new guidance outlines two principles for the judicious use of antimicrobial drugs in food-animal production:

  1. The use of medically important antimicrobial drugs in food-producing animals should be limited to those uses that are considered necessary for assuring animal health; and
  2. The use of medically important antimicrobial drugs in food-producing animals should be limited to those uses that include veterinary oversight or consultation. 

Seemingly sensible, this voluntary guidance has nonetheless elicited cries of protest from Big Ag interests like the National Pork Council and the National Cattlemen’s Beef Association. McKenna argues that by the time a pig strain of MRSA was discovered in 2004, the continued use of antibiotics was a matter of maintaining the status quo rather than a question of public health. CAFOs had become so economically dependent on subtherapeutic uses of antibotics for their production that it was impossible to stop. Says McKenna, “Antibiotics were the only way to keep livestock healthy long enough to efficiently put on weight.” 

By issuing its recent guidance, FDA has taken a step forward in recognizing what McKenna says “may be the most frightening epidemic since AIDS.” But if the CAFO industry does not comply voluntarily, the FDA should pass mandatory rules to control the use of antibiotics in animal production. Superbug provides a vivid and gripping account of the spread of MRSA and should be required reading at the FDA.

Yee Huang, Policy Analyst, Center for Progressive Reform. Bio.

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