A series of maps were developed to depict the shipment of individual retail meat types within the NARMS states during 2012–2014. Using locations gathered through MPI queries and the NARMS database, the researchers aggregated processors and retailers to the state level. Individual retail meat collections were stratified based upon their path, from processor to retail, and connected with an arched line. Those pathways were then evaluated for prevalence of MDR bacterial contamination.

A total of 11,243 meat samples were included in the final analyzed dataset. Data for ground turkey were collected most frequently, accounting for 36.9 percent of samples, followed by chicken breast (33.2 percent), ground beef (19.3 percent), and pork chops at (10.6 percent). The region where most meat samples were processed was in the South (44.3 percent of samples), followed by the Midwest (27 percent), the West (18.3 percent), and the Northeast (10.4 percent). The average distance that meat traveled from processor to retailer was 619.25 miles (approximately 997 kilometers).

Overall, retail meats included in the analysis were neither processed nor distributed equally across the U.S., and the researchers identified a potential association between distance traveled and prevalence of MDR bacteria, which might suggest a role for shipment distance in MDR bacterial contamination. Southern processors had the highest MDR bacterial contamination among chicken breast (11.1 percent), ground turkey (45.3 percent), and ground pork (6 percent). Regarding individual states, New York had the highest MDR Salmonella prevalence (48 percent), Pennsylvania had the highest MDR Campylobacter contamination levels (3.4 percent), Oregon had the highest MDR Escherichia coli contamination (38.9 percent), and Maryland had the highest MDR Enterococcus contamination (3 percent). The proportion of MDR bacterial contamination was similar across distances for both Salmonella and Campylobacter contamination. Increased distance was associated with increased MDR bacterial contamination both among all retail meat samples and those contaminated.

Limited evidence exists to explain regional differences associated with MDR bacterial contamination on retail meat. Upstream factors, such as husbandry practices, are shown to vary the bacteria harbored on the animals that enter the processor facilities, which could alter bacterial contamination on the final product. For example, some states have many more USDA-Certified Organic farms than others. There are also differences in state-specific humane slaughter laws and inspection programs. Although microbial contamination of retail meat is known to occur from slaughtering procedures, any differences in contamination as a result of state-specific humane laws and inspection programs is unknown and, therefore an opportunity for further research.

Regardless of the underlying reason, properly kept data, when available and transparent, could provide traceback information to identify individual processor entities and their facility locations and potentially be used to intervene and decrease exposures from MDR bacteria-contaminated retail meat.

A hypothesis for why longer distances traveled results in greater MDR pathogen contamination is the increased risks for gaps in a continuous cold chain and humidity control with longer transit times of refrigerated trucks. Additionally, after transportation, retailer conditions might similarly impact bacterial growth on retail meat products.