E. coli O157:H7 is one of hundreds of strains of the bacterium Escherichia coli.[1] Most strains of E. coli are harmless and live as normal flora in the intestines of healthy humans and animal.[2] The E. coli bacterium is among the most extensively studied microorganism.[3] The combination of letters and numbers in the name of the E. coli O157:H7 refers to the specific markers found on its surface and distinguishes it from other types of E. coli.[4] The testing done to distinguish E. coli O157:H7 from its other E. coli counterparts is called serotyping.[5] Pulsed-field gel electrophoresis (“PFGE”),[6]sometimes also referred to as genetic fingerprinting, is used to compare E. coli O157:H7 isolates to determine if the strains are distinguishable.[7]
E. coli O157:H7 was first recognized as a pathogen in 1982 during an investigation into an outbreak of hemorrhagic colitis[8]associated with consumption of hamburgers from a fast food chain restaurant.[9] Retrospective examination of more than three thousand E. coli culturesobtained between 1973 and 1982 found only one isolationwith serotype O157:H7, and that was a casein 1975.[10] In the ten years that followed there were approximately thirty outbreaks recorded in the United States.[11] This number is likely misleading, however, because E. coli O157:H7 infections did not become a reportable disease in any state until 1987 when Washington became the first state to mandate its reporting.[12] As a result, only the most geographically concentrated outbreak would have garnered enough notice to prompt further investigation.[13]
The virulence of E. coli O157:H7 is a result of its ability to produce Shiga-like toxins.[14] It has been theorized that generic E. coli picked up this deadly ability through horizontal transfer of virulence genes from the Shigella bacteria.[15] Genome sequencing of E. coli O157:H7 has since confirmed that gene transfer did in fact occur, and that the evolution of ever more virulent forms of bacteria will likely continue to occur.[16] The prospect of emerging pathogens as a significant public health threat has been emphasized by the CDC for some time.[17]
Foods of a bovine origin are the most common cause of both outbreaks and sporadic cases of E. coli O157:H7 infections.[18] Surveys performed on feed lots have demonstrated that cattle can be infected with E. coli O157:H7 through close contact, and under muddy conditions.[19] The prevalence of E. coli O157:H7 among cattle in these feed lots can reach 63-100%, especially during the summer.[20] The prevalence of E. coli O157:H7 in the summer, which is when outdoor grilling of hamburgers becomes most common, is a significant public safety risk.
According to a recent study, an “estimated 73,480 illnesses due to E. coli O157:H7 infections occur each year in the United States, leading to an estimated 2,168 hospitalizations and sixty-one deaths annually.”[21] The hemorrhagic colitis caused by E. coli O157:H7 is characterized by severe abdominal cramps, diarrhea that typically turns bloody within twenty-four hours, and sometimes fever.[22] The typical incubation period—which is to say the time from exposure to the onset of symptoms—in outbreaks is usually reported as three to eight days.[23] Infection can occur in people of all ages but is most common in children.[24] The duration of an uncomplicated illness can range from one to twelve days.[25] In reported outbreaks, the rate of death is 0-2%, with rates running as high as 16-35% in outbreaks involving the elderly, like those at nursing homes.[26]
What makes E. coli O157:H7 truly and decidedly deadly is its very low infectious dose,[27] and how relatively difficult it is to kill these bacteria.[28] Unlike Salmonella, for example, which usually requires something approximating an “egregious food handling error, E. coli O157:H7 in ground beef that is only slightly undercooked can result in infection.”[29] As few as twenty organisms have been said to be sufficient to infect a person and, as a result, possibly kill them.[30] And unlike generic E. coli, the O157:H7 serotype multiplies at temperatures up to 44° Fahrenheit, survives freezing and thawing, is heat resistant, grows at temperatures up to 111° Fahrenheit, resists drying, and can survive exposure to acidic environments.[31]
And, finally, to make it even more of a dangerous threat, E. coli O157:H7 bacteria are easily transmitted by person-to-person contact.[32] There is also the serious risk of cross-contamination between raw meat and other food items intended to be eaten without cooking.Indeed, a principle and consistent criticism of the USDA E. coli O157:H7 policy is the fact that it has failed to focus on the risks of cross-contamination versus that posed by so-called improper cooking.[33] With this pathogen, there is ultimately no real margin of error, and the cost of error can be death. It is for this precise reason that the USDA has repeatedly rejected calls from the meat industry to hold consumers responsible for E. coli O157:H7 surviving the cooking process.
See footnotes below