Pigs, their manure and their handlers are frequently targeted as the source of antibiotic resistance, but recent research in Sweden suggests humans are to blame.
A five-year study by Sweden’s National Veterinary Institute (SVA) analyzed samples of extended spectrum beta-lactamase (ESBL), a type of enzyme known to confer resistance to beta-lactam antibiotics, including penicillin and cephalosporins. The samples were obtained from domestic and imported foods, farm animals, healthy volunteers, severely ill patients, the environment and sewage water.
From these 5,300 samples, researchers identified three separate populations of ESBL: one in Swedish food and farm animals, one in imported foods and one in humans and the environment. Results indicate that only 6 percent of isolates were ESBLa, which are attributed to farm animals, while the majority of isolates were ESBLm, which are found only in humans. The ESBL genes in the general community population, sewage water and the environment have an appoximately 90 percent similarity.
The data also show that animals are associated with a human infection rate of only 0.00022 percent on a population basis, or 85 people in a population of 100,000. Based on these findings, the SVA, together with Sweden’s Public Health Agency and National Food Agency, concluded that food is a limited contributor to antibiotic-resistant E. coli infections in humans.
In fact, the potential overlap between clinical human isolates and isolates from healthy farm animals was found to be extremely unlikely, according to SVARM 2014, a report responsible for measuring the consumption of antibiotics and occurance of antibiotic resistance in Sweden.