Airborne antimicrobials cause concern

Researchers have discovered that antimicrobials given to pigs in feed can end up in dust clouds that swirl inside swine housing. While past studies have found farm-derived antimicrobials in waterways and food products, the new study, published online June 18 in the journal Environmental Health Perspectives, now finds that these drugs can also spread through the air.

Swine housing dust originates from feed, bedding, feces, and the animals themselves. Research has shown that veterinarians and other people who work at such operations develop severe respiratory problems from exposure to dust that contains microorganisms, endotoxins, and allergens (see JAVMA, Sept. 15, 2003, page 758). According to researchers of the new study, further risks may arise from inhalation of dust contaminated with a mixture of antimicrobials.

In a retrospective study, German researchers collected dust samples from a pig finishing farm, between 1981 and 2000, and analyzed them for various antimicrobials. In 18 of 20 samples, they detected up to five drugs, including tylosin, various tetracyclines, sulfamethazine, and chloramphenicol. Total concentrations ranged from 0.2 mg/kg to 12.5 mg/kg dust.

Gerd Hamscher, a food chemist with a special interest in analytic chemistry at the Hannover School of Veterinary Medicine in Germany, led the study. Hamscher, who holds a doctorate in his field, says he was surprised that they found at least one compound in 90 percent of the samples. "The concentrations found in dust were relatively high when compared to other environmental compartments, such as surface water or soil," he said.

According to the researchers, antimicrobial dust clouds may contribute to farm workers' allergies. Humans are known to be sensitive to tylosin and sulfamethazine, for example, and these drugs were found in 80 percent and 65 percent of the samples, respectively.

The findings are also of concern because of the possible fate, in terms of effectiveness, of human and veterinary antimicrobials. Ongoing exposure to subtherapeutic concentrations of various antimicrobials create optimal conditions for the development of antimicrobial resistance, say the researchers.

Dr. Hamscher emphasizes, however, that further studies are needed. "It is too early to quantify the health hazards for farmers," he said. "We discussed, in the paper, allergic reactions and the development of antibiotic resistance, but additional studies are required to check these hypotheses." He recommends studying dust in larger pig production systems and hen houses, which also have dust problems. In addition, farm workers should be monitored for antimicrobial resistance.