With at least 4 hospitalized, there were likely more that a few “Sleepless” nights in Seattle. So, what do you need to know about E. coli?
E. coli is an archetypal commensal bacterial species that lives in mammalian intestines. E. coli O157:H7 is one of thousands of serotypes Escherichia coli.[1] The combination of letters and numbers in the name of the E. coli O157:H7 refers to the specific antigens (proteins which provoke an antibody response) found on the body and tail or flagellum[2]respectively and distinguish it from other types of E. coli.[3] Most serotypes of E. coli are harmless and live as normal flora in the intestines of healthy humans and animals.[4] The E. coli bacterium is among the most extensively studied microorganism.[5] The testing done to distinguish E. coli O157:H7 from its other E. coli counterparts is called serotyping.[6] Pulsed-field gel electrophoresis (PFGE),[7] sometimes also referred to as genetic fingerprinting, is used to compare E. coli O157:H7 isolates to determine if the strains are distinguishable.[8] A technique called multilocus variable number of tandem repeats analysis (MLVA) is used to determine precise classification when it is difficult to differentiate between isolates with indistinguishable or very similar PFGE patterns.[9]
E. coli O157:H7 was first recognized as a pathogen in 1982 during an investigation into an outbreak of hemorrhagic colitis[10] associated with consumption of hamburgers from a fast food chain restaurant.[11] Retrospective examination of more than three thousand E. coli cultures obtained between 1973 and 1982 found only one (1) isolationwith serotype O157:H7, and that was a case in 1975.[12] In the ten (10) years that followed there were approximately thirty (30) outbreaks recorded in the United States.[13] This number is likely misleading, however, because E. coliO157:H7 infections did not become a reportable disease in any state until 1987 when Washington became the first state to mandate its reporting to public health authorities.[14] As a result, only the most geographically concentrated outbreak would have garnered enough notice to prompt further investigation.[15]
E. coli O157:H7’s ability to induce injury in humans is a result of its ability to produce numerous virulence factors, most notably Shiga-like toxins.[16] Shiga toxin (Stx) has multiple variants (e.g. Stx1, Stx2, Stx2c), and acts like the plant toxin ricin by inhibiting protein synthesis in endothelial and other cells.[17] Shiga toxin is one of the most potent toxins known.[18] In addition to Shiga toxins, E. coli O157:H7 produces numerous other putative virulence factors including proteins, which aid in the attachment and colonization of the bacteria in the intestinal wall and which can lyse red blood cells and liberate iron to help support E. coli metabolism.[19]
E. coli O157:H7 evolved from enteropathogenic E. coli serotype O55:H7, a cause of non-bloody diarrhea, through the sequential acquisition of phage-encoded Stx2, a large virulence plasmid, and additional chromosomal mutations.[20]The rate of genetic mutation of E. coli O157:H7 indicates that the common ancestor of current E. coli O157:H7 clades[21] likely existed some 20,000 years ago.[22] E. coli O157:H7 is a relentlessly evolving organism,[23] constantly mutating and acquiring new characteristics, including virulence factors that make the emergence of more dangerous variants a constant threat.[24] The CDC has emphasized the prospect of emerging pathogens as a significant public health threat for some time.[25]
Although foods of a bovine origin are the most common cause of both outbreaks and sporadic cases of E. coliO157:H7 infections[26], outbreak of illnesses have been linked to a wide variety of food items. For example, produce has, since at least 1991, been the source of substantial numbers of outbreak-related E. coli O157:H7 infections.[27] Other unusual vehicles for E. coli O157:H7 outbreaks have included unpasteurized juices, yogurt, dried salami, mayonnaise, raw milk, game meats, sprouts, and raw cookie dough.[28]
According to a recent study, an estimated 93,094 illnesses are due to domestically acquired E. coli O157:H7 each year in the United States.[29] Estimates of foodborne acquired O157:H7 cases result in 2,138 hospitalizations and 20 deaths annually.[30] The colitis caused by E. coli O157:H7 is characterized by severe abdominal cramps, diarrhea that typically turns bloody within twenty-four (24) hours, and sometimes fevers.[31] The incubation period—which is to say the time from exposure to the onset of symptoms—in outbreaks is usually reported as three (3) to four (4) days, but may be as short as one (1) day or as long as ten (10) days.[32] Infection can occur in people of all ages but is most common in children.[33] The duration of an uncomplicated illness can range from one (1) to twelve (12) days.[34] 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 have occurred at nursing homes.[35]
What makes E. coli O157:H7 remarkably dangerous is its very low infectious dose,[36] and how relatively difficult it is to kill these bacteria.[37] 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,”[38] as few as twenty (20) organisms may be sufficient to infect a person and, as a result, possibly kill them.[39] And unlike generic E. coli, the O157:H7 serotype multiplies at temperatures up to 44°F, survives freezing and thawing, is heat resistant, grows at temperatures up to 111°F, resists drying, and can survive exposure to acidic environments.[40]
And, finally, to make it even more of a threat, E. coli O157:H7 bacteria are easily transmitted by person-to-person contact.[41] 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.[42] With this pathogen, there is ultimately no margin of error. It is for this precise reason that the USDA has repeatedly rejected calls from the meat industry to hold consumers primarily responsible for E. coli O157:H7 infections caused, in part, by mistakes in food handling or cooking.[43]
[1] E. coli bacteria were discovered in the human colon in 1885 by German bacteriologist Theodor Escherich. Feng, Peter, Stephen D. Weagant, Michael A. Grant, Enumeration of Escherichia coli and the Coliform Bacteria, in BACTERIOLOGICAL ANALYTICAL MANUAL (8th Ed. 2002), http://www.cfsan.fda.gov/~ebam/bam-4.html. Dr. Escherich also showed that certain strains of the bacteria were responsible for infant diarrhea and gastroenteritis, an important public health discovery. Id. Although the bacteria were initially called Bacterium coli, the name was later changed to Escherichia coli to honor its discoverer. Id.
[2] Not all E. coli are motile. For example, E. coli O157:H7 which lack flagella are thus E. coli O157:NM for non-motile.
[3] CDC, Escherichia coli O157:H7, General Information, Frequently Asked Questions: What is Escherichia coli O157:H7?, http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm.
[4] Marion Nestle, Safe Food: Bacteria, Biotechnology, and Bioterrorism, 40-41 (1st Pub. Ed. 2004).
[5] James M. Jay, MODERN FOOD MICROBIOLOGY at 21 (6th ed. 2000). (“This is clearly the most widely studied genus of all bacteria.”)
[6] Beth B. Bell, MD, MPH, et al. A Multistate Outbreak of Escherichia coli O157:H7-Associated Bloody Diarrhea and Hemolytic Uremic Syndrome from Hamburgers: The Washington Experience, 272 JAMA (No. 17) 1349, 1350 (Nov. 2, 1994) (describing the multiple step testing process used to confirm, during a 1993 outbreak, that the implicated bacteria were E. coli O157:H7).
[7] Jay, supra note 5, at 220-21 (describing in brief the PFGE testing process).
[8] Id. Through PFGE testing, isolates obtained from the stool cultures of probable outbreak cases can be compared to the genetic fingerprint of the outbreak strain, confirming that the person was in fact part of the outbreak. Bell, supra note 6, at 1351-52. Because PFGE testing soon proved to be such a powerful outbreak investigation tool, PulseNet, a national database of PFGE test results was created. Bala Swaminathan, et al. PulseNet: The Molecular Subtyping Network for Foodborne Bacterial Disease Surveillance, United States, 7 Emerging Infect. Dis. (No. 3) 382, 382-89 (May-June 2001) (recounting the history of PulseNet and its effectiveness in outbreak investigation).
[9] Konno T. et al. Application of a multilocus variable number of tandem repeats analysis to regional outbreak surveillance of Enterohemorrhagic Escherichia coli O157:H7 infections. Jpn J Infect Dis. 2011 Jan; 64(1): 63-5.
[10] “[A] type of gastroenteritis in which certain strains of the bacterium Escherichia coli (E. coli) infect the large intestine and produce a toxin that causes bloody diarrhea and other serious complications.” The Merck Manual of Medical Information, 2nd Home Ed. Online, http://www.merck.com/mmhe/sec09/ch122/ch122b.html.
[11] L. Riley, et al. Hemorrhagic Colitis Associated with a Rare Escherichia coli Serotype, 308 New. Eng. J. Med. 681, 684-85 (1983) (describing investigation of two outbreaks affecting at least 47 people in Oregon and Michigan both linked to apparently undercooked ground beef). Chinyu Su, MD & Lawrence J. Brandt, MD, Escherichia coli O157:H7 Infection in Humans, 123 Annals Intern. Med. (Issue 9), 698-707 (describing the epidemiology of the bacteria, including an account of its initial discovery).
[12] Riley, supra note 11 at 684. See also Patricia M. Griffin & Robert V. Tauxe, The Epidemiology of Infections Caused by Escherichia coliO157:H7, Other Enterohemorrhagic E. coli, and the Associated Hemolytic Uremic Syndrome, 13 Epidemiologic Reviews 60, 73 (1991).
[13] Peter Feng, Escherichia coli Serotype O157:H7: Novel Vehicles of Infection and Emergence of Phenotypic Variants, 1 Emerging Infect. Dis. (No. 2), 47, 47 (April-June 1995) (noting that, despite these earlier outbreaks, the bacteria did not receive any considerable attention until ten years later when an outbreak occurred 1993 that involved four deaths and over 700 persons infected).
[14] William E. Keene, et al. A Swimming-Associated Outbreak of Hemorrhagic Colitis Caused by Escherichia coli O157:H7 and Shigella Sonnei, 331 New Eng. J. Med. 579 (Sept. 1, 1994). See also Stephen M. Ostroff, MD, John M. Kobayashi, MD, MPH, and Jay H. Lewis, Infections with Escherichia coli O157:H7 in Washington State: The First Year of Statewide Disease Surveillance, 262 JAMA (No. 3) 355, 355 (July 21, 1989). (“It was anticipated the reporting requirement would stimulate practitioners and laboratories to screen for the organism.”)
[15] See Keene, supra note 14 at 583. (“With cases scattered over four counties, the outbreak would probably have gone unnoticed had the cases not been routinely reported to public health agencies and investigated by them.”) With improved surveillance, mandatory reporting in 48 states, and the broad recognition by public health officials that E. coli O157:H7 was an important and threatening pathogen, there were a total of 350 reported outbreaks from 1982-2002. Josef M. Rangel, et al. Epidemiology of Escherichia coli O157:H7 Outbreaks, United States, 1982-2002, 11 Emerging Infect. Dis. (No. 4) 603, 604 (April 2005).
[16] Griffin & Tauxe, supra note 12, at 61-62 (noting that the nomenclature came about because of the resemblance to toxins produced by Shigella dysenteries).
[17] Sanding K, Pathways followed by ricin and Shiga toxin into cells, Histochemistry and Cell Biology, vol. 117, no. 2:131-141 (2002). Endothelial cells line the interior surface of blood vessels. They are known to be extremely sensitive to E. coli O157:H7, which is cytotoxigenic to these cells making them a primary target during STEC infections.
[18] Johannes L, Shiga toxins—from cell biology to biomedical applications. Nat Rev Microbiol 8, 105-116 (February 2010). Suh JK, et al. Shiga Toxin Attacks Bacterial Ribosomes as Effectively as Eucaryotic Ribosomes, Biochemistry, 37 (26); 9394–9398 (1998).
[19] Welinder-Olsson C, Kaijser B. Enterohemorrhagic Escherichia coli (EHEC). Scand J. Infect Dis. 37(6-7): 405-16 (2005). See alsoUSDA Food Safety Research Information Office E. coli O157:H7 Technical Fact Sheet: Role of 60-Megadalton Plasmid (p0157) and Potential Virulence Factors, http://fsrio.nal.usda.gov/document_fsheet.php?product_id=225.
[20] Kaper JB and Karmali MA. The Continuing Evolution of a Bacterial Pathogen. PNAS vol. 105 no. 12 4535-4536 (March 2008). Wick LM, et al. Evolution of genomic content in the stepwise emergence of Escherichia coli O157:H7. J Bacteriol 187:1783–1791(2005).
[21] A group of biological taxa (as species) that includes all descendants of one common ancestor.
[22] Zhang W, et al. Probing genomic diversity and evolution of Escherichia coli O157 by single nucleotide polymorphisms. Genome Res 16:757–767 (2006).
[23] Robins-Browne RM. The relentless evolution of pathogenic Escherichia coli. Clin Infec Dis. 41:793–794 (2005).
[24] Manning SD, et al. Variation in virulence among clades of Escherichia coli O157:H7 associated with disease outbreaks. PNAS vol. 105 no. 12 4868-4873 (2008). (“These results support the hypothesis that the clade 8 lineage has recently acquired novel factors that contribute to enhanced virulence. Evolutionary changes in the clade 8 subpopulation could explain its emergence in several recent foodborne outbreaks; however, it is not clear why this virulent subpopulation is increasing in prevalence.”)
[25] Robert A. Tauxe, Emerging Foodborne Diseases: An Evolving Public Health Challenge, 3 Emerging Infect. Dis. (No. 4) 425, 427 (Oct.-Dec. 1997). (“After 15 years of research, we know a great deal about infections with E. coli O157:H7, but we still do not know how best to treat the infection, nor how the cattle (the principal source of infection for humans) themselves become infected.”)
[26] CDC, Multistate Outbreak of Escherichia coli O157:H7 Infections Associated With Eating Ground Beef—United States, June-July 2002, 51 MMWR 637, 638 (2002) reprinted in 288 JAMA (No. 6) 690 (Aug. 14, 2002).
[27] Rangel, supra note 15, at 605.
[28] Feng, supra note 13, at 49. See also USDA Bad Bug Book, Escherichia coli O157:H7, http://www.fda.gov/food/foodsafety/foodborneillness/foodborneillnessfoodbornepathogensnaturaltoxins/badbugbook/ucm071284.htm.
[29] Scallan E, et al. Foodborne illness acquired in the United States –major pathogens, Emerging Infect. Dis. Jan. (2011), http://www.cdc.gov/EID/content/17/1/7.htm.
[30] Id., Table 3.
[31] Griffin & Tauxe, supra note 12, at 63.
[32] Centers for Disease Control, Division of Foodborne, Bacterial and Mycotic Diseases, Escherichia coli general information, http://www.cdc.gov/nczved/dfbmd/disease_listing/stec_gi.html. See also PROCEDURES TO INVESTIGATE FOODBORNE ILLNESS, 107 (IAFP 5th Ed. 1999) (identifying incubation period for E. coli O157:H7 as “1 to 10 days, typically 2 to 5”).
[33] Su & Brandt, supra note 11 (“the young are most often affected”).
[34] Tauxe, supra note 25, at 1152.
[35] Id.
[36] Griffin & Tauxe, supra note 12, at 72. (“The general patterns of transmission in these outbreaks suggest that the infectious dose is low.”)
[37] V.K. Juneja, O.P. Snyder, A.C. Williams, and B.S. Marmer, Thermal Destruction of Escherichia coli O157:H7 in Hamburger, 60 J. Food Prot. (vol. 10). 1163-1166 (1997) (demonstrating that, if hamburger does not get to 130°F, there is no bacterial destruction, and at 140°F, there is only a 2-log reduction of E. coli present).
[38] Griffin & Tauxe, supra note 12, at 72 (noting that, as a result, “fewer bacteria are needed to cause illness that for outbreaks of salmonellosis”). Nestle, supra note 4, at 41. (“Foods containing E. coli O17:H7 must be at temperatures high enough to kill all of them.”) (italics in original)
[39] Patricia M. Griffin, et al. Large Outbreak of Escherichia coli O157:H7 Infections in the Western United States: The Big Picture, in RECENT ADVANCES IN VEROCYTOTOXIN-PRODUCING ESCHERICHIA COLI INFECTIONS, at 7 (M.A. Karmali & A. G. Goglio eds. 1994). (“The most probable number of E. coli O157:H7 was less than 20 organisms per gram.”) There is some inconsistency with regard to the reported infectious dose. Compare Chryssa V. Deliganis, Death by Apple Juice: The Problem of Foodborne Illness, the Regulatory Response, and Further Suggestions for Reform, 53 Food Drug L.J. 681, 683 (1998) (“as few as ten”) with Nestle, supra note 4, at 41 (“less than 50”). Regardless of these inconsistencies, everyone agrees that the infectious dose is, as Dr. Nestle has put it, “a miniscule number in bacterial terms.” Id.
[40] Nestle, supra note 4, at 41.
[41] Griffin & Tauxe, supra note 12, at 72. The apparent “ease of person-to-person transmission…is reminiscent of Shigella, an organism that can be transmitted by exposure to extremely few organisms.” Id. As a result, outbreaks in places like daycare centers have proven relatively common. Rangel, supra note 15, at 605-06 (finding that 80% of the 50 reported person-to-person outbreak from 1982-2002 occurred in daycare centers).
[42] See, e.g. National Academy of Science, Escherichia coli O157:H7 in Ground Beef: Review of a Draft Risk Assessment, Executive Summary, at 7 (noting that the lack of data concerning the impact of cross-contamination of E. coli O157:H7 during food preparation was a flaw in the Agency’s risk-assessment), http://www.nap.edu/books/0309086272/html/.
[43] Kriefall v. Excel, 265 Wis.2d 476, 506, 665 N.W.2d 417, 433 (2003). (“Given the realities of what it saw as consumers’ food-handling patterns, the [USDA] bored in on the only effective way to reduce or eliminate food-borne illness”—i.e., making sure that “the pathogen had not been present on the raw product in the first place.”) (citing Pathogen Reduction, 61 Fed. Reg. at 38966).