A new study published in the U.S. Centers for Disease Control and Prevention’s Emerging Infectious Diseases links a new strain of methicillin-resistant Staphylococcus aureus (MRSA), once found only in pigs, to more than 20 percent of all human MRSA infections in the Netherlands (the study can be found at http://www.cdc.gov/eid/content/13/12/1834.htm).

The new strain of MRSA, NT-MRSA, emerged in the Netherlands in 2003 and increased steadily until by 2006 it accounted for more than one out of every five human MRSA infections, many of them in either pig farmers or cattle farmers. The NT-MRSA cases clustered in regions of the country with high densities of pig and cattle farms. The new strain has high rates of hospitalization, suggesting that it causes severe disease.

Research published this fall in Veterinary Microbiology found MRSA was also prevalent in Canadian pigs and pig farmers, pointing again to animal agriculture as a source of the deadly bacteria.

Despite these studies and others from Europe dating back to 2005, the United States does not systematically test pigs, cattle, and other food animals for MRSA. As a result, the US public health establishment does not know whether the use of antibiotics in food animals in the United States is contributing to the reported surge of MRSA cases in the United States.

A study published earlier in the Journal of the American Medical Association (JAMA) estimated almost 100,000 MRSA infections in the United States in 2005, nearly 19,000 of them fatal. In comparison, HIV/AIDS killed 17,000 people that year.

Members of the Keep Antibiotics Working coalition (KAW), including medical, agriculture, and environmental experts, are repeating their call for Congress to compel the U.S. Food and Drug Administration to determine whether swine, cattle and poultry harbor MRSA in the US and could be reservoirs from which infections are making their way into the community.

 “Antibiotic resistance is exploding in our hospitals and communities. Medical experts point to the profligate use of antibiotics in animal feed as a significant cause, but those in charge of safeguarding our food system are mostly just whistling in the dark,” said Rebecca Goldburg, senior scientist at Environmental Defense.

The heavy use of antibiotics in industrialized livestock operations can select for resistant bacteria, such as MRSA. The Union of Concerned Scientists estimates that 70 percent of all the antibiotics and related drugs used in the United States are used as feed additives for chicken, hogs, and beef cattle. Antibiotics use in pig farms in the Netherlands is believed to be facilitating the spread of MRSA there.

Proposed federal legislation would phase out the use of antibiotics that are important in human medicine as animal feed additives within two years. The Preservation of Antibiotics for Medical Treatment Act is sponsored by Senate Health Committee Chairman Edward Kennedy (D-Mass.) and Senators Olympia Snowe (R-Maine), Susan Collins (R-Maine), Sherrod Brown (D-Ohio) and Jack Reed (D-R.I.) in the Senate (S. 549) and Rep. Louise Slaughter (D-N.Y.), the only microbiologist in Congress, and 34 other House members in the U.S. House of Representatives (H.R. 962).

The American Medical Association, the Infectious Diseases Society of America, and the American Academy of Pediatrics are among the more than 350 health, agriculture, and other groups nationwide that have endorsed this bill.