Investigation of Occupational Exposure to and Infection by MRSA in Rural Iowa.

摘要

A recent report has documented the clinical impact of methicillin-resistant Staphylococcus aureus (MRSA), suggesting that MRSA caused over 94,000 invasive infections and more than 18,000 deaths in the United States in 2005, eclipsing HIV as a leading infectious disease killer. In 2005, the majority of these infections were associated with healthcare exposure; however, this trend is changing, and new groups at risk of acquiring MRSA have emerged. Initially individuals with health care contact were the main risk group for MRSA carriage and infection; however, in the past decade, athletes, injection drug users, and prisoners have also emerged as groups at risk of MRSA infection. The most recent occupational group identified as at-risk for MRSA infection are individuals in contact with live swine and other animals. As such, we examined the presence and molecular types of S. aureus on swine farms in Iowa using environmental sampling and before/after self-swabs of veterinary students on swine rotations through these farms; examined airborne transmission within swine barns using Andersen sampling, and the potential for a biofilter system to mitigate risk of transmission of this bacterium; and examined MRSA infections in patients in a livestock-dense area of the state. MRSA was detected in 30% of the pork farms and in 22% of the students following an exposure to a MRSA-positive pork farm. All students found to be MRSA-positive initially following farm visit were negative for MRSA within 24 hours post visit, suggesting short duration of carriage via farm exposure or contamination rather than biological contamination. Most common spa types recovered were t002 (79%), t034 (16%) and t548 (4%). MRSA was also detected within a swine facility, mostly large particles (>5um), which tend to be associated with feed. This was also detected in small particles (<5um) 215 meters downwind of a swine facility. These smaller particles tend to be associated with dried feces and shed skin cells. Feed itself was also tested and was positive for MRSA even prior to entering the facility, suggesting that feed imported onto farms may itself be a source of MRSA in the facility. Mitigation of MRSA with a wood chip-based biofilter was also examined. Both hardwood chips and western red cedar chips were effective at preventing the emission of viable MRSA particles in the exhaust air from swine feeding facilities. Efficiency ranged from 77 percent of particles with mean particle size of 1.6 um to 100 percent using western red cedar media with particles with a mean size of 5.85 um. As such, these inexpensive filters may provide a way to reduce transmission of MRSA into the external air, but additional means are needed to reduce the burden of MRSA within barns. Finally, an examination was made of cases of MRSA reporting to a physician's clinic in western Iowa, in a swine-dense area. Fifteen case patients were enrolled with 10 total samples received from the clinic as possible MRSA infections. S. aureus was positively identified in 4 samples. None were identified as common livestock-associated (LA) strains.