Methicillin Resistant Staphylococcus aureus: A Growing Link between MRSA Infections and Pigs
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That methicillin resistant Staphylococcus aureus (MRSA) is in the news again is not surprising. However, to my knowledge, Nicholas Kristof‘s article in today’s New York Times may be the first Op-Ed piece written by a non-scientist about the growing threat and seriousness of MRSA infections. Mr. Kristof apparently became aware of MRSA when he was contacted by Tom Anderson, MD, a Camden, Indiana physician who was experiencing “phenomenal levels of MRSA infections" in his community.
Beginning in the early 1990s, Dr Anderson noticed a rapidly rising incidence in the number of community acquired skin infections caused by MRSA among his patients. Most of Dr Anderson’s patients were swine farmers—the predominant industry in Camden. At first puzzled by the growing incidences of MRSA outbreaks, Dr. Anderson began to suspect that his patient’s pigs may be the source of growing number of cases of MRSA skin infections. He was reluctant to alert public health officials about his suspicions because any hint livestock-related health issues might jeopardize the livelihood of many of his neighbors and friends. By last fall, however, Camden’s MRSA epidemic had grown so large that Dr. Anderson could no longer remain silent. Rather than alert the authorities himself, he decided to invite Mr. Kristof, an investigative reporter, to visit him in Camden and break the story. Unfortunately, before Mr. Kristof could visit, Dr. Anderson died abruptly at age 54. There was no autopsy, but a blood test suggested he may have died from a heart attack or aneurysm. And—this is where the story gets interesting—a recent Dutch study has linked porcine MRSA isolates to a case of human endocarditis. Dr. Anderson had himself suffered at least three bouts of MRSA infections.
In another Dutch study conducted in 2004, MRSA strain ST398 (which caused the endocarditis in the more recent study) was isolated from three family members, three farm workers and 8 of 10 pigs from a single farm. Since then, strain ST398 has spread rapidly through the Netherlands — especially in swine-producing areas— and pig farmers there are 760 times more likely than the general population to carry MRSA. More recently, a study conducted by public health officials in Ontario, Canada showed that 20% of pig farmers were colonized by strains of MRSA genetically identical to those isolated from European pigs. Finally, a 2008 study conducted in Iowa, reported that strain ST398 was isolated from 45 percent of pig farmers and 49 percent of hogs that were tested. Together, these studies suggest that colonization of swine by MRSA and pig farmers is very common and that swine (and possibly other agricultural animals) could become an important reservoir for strains of MRSA.
While not conclusive, most infectious diseases experts believe that the emergence of MRSA and antibiotic resistant bacteria can be directly linked to the widespread and rampant use of antibiotics as growth enhancers in livestock feed. Despite the alarming emergence of multiple antibiotic resistance bacteria, livestock producers in the US and elsewhere continue to add antibiotics to livestock feeds. This led Mr. Kristof to lament that “we as a nation have moved to a model of agriculture that produces cheap bacon but risks the health of all of us.” Not surprisingly, as is frequently the case, big business has chosen to place profits before the health and safety of society.
Until next time...
Good Luck and Good Reading (look for Mr. Kristof’s Sunday column on the emergence of antibiotic resistant "superbugs")
Vincent Racaniello
