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Another Reason to Hold Your Breath Around Corporate Hog Farms

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Science Letter

December 28, 2004

Multidrug-resistant bacteria airborne in concentrated swine operation


People could be exposed to antibiotic-resistant bacteria from breathing
the air from concentrated swine feeding facilities, according to
researchers at the Johns Hopkins Bloomberg School of Public Health.

They detected bacteria resistant to at least two antibiotics in air
samples collected from inside a large-scale swine operation in the
Mid-Atlantic region of the United States. Until now, little research has
been conducted regarding the presence of antibiotic-resistant bacteria
in the air within industrial swine facilities.

The study adds to the understanding of various pathways in which humans
can be exposed to antibiotic-resistant bacteria, such as consumption of
retail pork products and contact with or ingestion of soil, surface
water and groundwater near production operations. The article is
published in the online edition of Environmental Health Perspectives.

"Eating retail pork products is not the only pathway of exposure for the
transfer of antibiotic-resistant bacteria from swine to humans.
Environmental pathways may be equally important," said Amy Chapin, the
study's lead author and a doctoral candidate at the Bloomberg School of
Public Health's department of environmental health sciences.

Chapin explained that the use of antibiotics in industrial animal
production has a significant impact on the emergence of
antibiotic-resistant bacteria that threaten human health. Using
antibiotics in animals can decrease the effectiveness of the same
antibiotics used to combat human infections. The nontherapeutic use of
antimicrobials in livestock production in the United States comprises an
estimated 60 to 80% of the total antimicrobial production nationally.
Nontherapeutic doses of drugs are given to swine to promote growth and
improve feed efficiency - not to treat actual swine disease.

The airborne bacteria samples that were found to be multidrug-resistant
were: Enterococcus, coagulase-negative staphylococci and viridans group
streptococci. These bacteria are associated with a variety of human
infections. The study found that 98% of the isolated samples were
resistant to at least two of the following antibiotics: erythromycin,
clindamycin, virginiamycin and tetracycline. All of these drugs (or
their human drug counterparts) are important antibiotics in the
treatment of human infections. In contrast, none of the bacterial
samples were resistant to vancomycin - an antibiotic that has never been
approved for use in swine production in the United States.

The researchers believe workers at concentrated animal feeding
operations are at greatest risk for airborne exposure to
antibiotic-resistant bacteria. However, the same workers may also become
reservoirs of drug-resistant bacteria that can be spread to family and
the broader community. The study also raises questions about the spread
of drug-resistant bacteria to areas beyond the immediate site through
ventilation fans and by the application of manure from feeding
operations to off-site fields.

"These research findings add another piece to our understanding of human
exposure to antibiotic-resistant bacteria," said Kellogg Schwab, PhD,
assistant professor in the Bloomberg School of Public Health's
department of environmental health sciences and the study's
corresponding author. "Finding and documenting the multiple
environmental pathways of exposure are critical to finding solutions to
the growing, serious problem of antibiotic-resistant bacteria in
humans."