Escherichia coli O157 cluster evaluation.
We investigated a multistate cluster of Escherichia coli Escherichia coli (ĕsh'ərĭk`ēə kō`lī), common bacterium that normally inhabits the intestinal tracts of humans and animals, but can cause infection in other parts of the body, especially the urinary tract. O157:H7 isolates; pulsed-field gel electrophoresis gel electrophoresis
Electrophoresis performed in a gel composed of agarose, polyacrylamide, or starch. subtyping, using a single enzyme, suggested an epidemiologic association. An investigation and additional subtyping, however, did not support the association. Confirming E. coli E. coli: see Escherichia coli.
in full Escherichia coli
Species of bacterium that inhabits the stomach and intestines. E. coli can be transmitted by water, milk, food, or flies and other insects. O157 clusters with two or more restriction endonucleases is necessary before public health resources are allocated to follow-up investigations.
Escherichia coli O157:H7 is an important cause of foodborne infections estimated to cause 73,000 illnesses and 60 deaths annually in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. (1). Implementation of pulsed-field gel electrophoresis (PFGE PFGE Pulsed-Field Gel Electrophoresis ) molecular subtyping has greatly improved E. coli O157:H7 surveillance and detection of outbreaks (2). PFGE subtyping was initially used to identify related isolates and support epidemiologic associations during outbreak investigations. Public health laboratories in the United States now routinely subtype (programming) subtype - If S is a subtype of T then an expression of type S may be used anywhere that one of type T can and an implicit type conversion will be applied to convert it to type T. all E. coli O157:H7 isolates by PFGE as part of a national molecular subtyping network (PulseNet) (2) after this practice proved instrumental in identifying outbreaks not detected by traditional epidemiologic methods (3). PulseNet laboratories initially digest isolates with a single enzyme and compare the resulting PFGE patterns by using commercial software (BioNumerics, St. Martens-Latem, Belgium) to determine whether patterns are shared by multiple isolates. These patterns are then communicated electronically to the Centers for Disease Control and Prevention Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center. (CDC See Control Data, century date change and Back Orifice.
CDC - Control Data Corporation ) (Atlanta, GA), where PFGE patterns of isolates from different states are definitively compared. PulseNet policy states that isolates with potential epidemiologic significance that have indistinguishable patterns with a primary enzyme, should be digested with a secondary enzyme before extensive epidemiologic investigations are undertaken. Indistinguishable patterns should also be confirmed by submission to a central database (2). However, time constraints and the availability of sufficient resources prevent some laboratories from adhering to this policy.
On July 5, 2000, the Michigan Department of Community Health's laboratory notified CDC of a cluster of five E. coli O157:H7 isolates, collected from May 25 to June 21, 2000, which shared an indistinguishable XbaI PFGE pattern. PulseNet staff confirmed that these isolates' patterns were indistinguishable and designated the pattern as PulseNet pattern EXHX01.0047. In 2000, this PFGE pattern represented approximately 2% of the E. coli O157 patterns in the PulseNet database. These Michigan isolates possessed genes only for Shiga toxin Shiga toxins are a family of related toxins with two major groups, Stx1 and Stx2, whose genes are considered to be part of the genome of lambdoid prophages. The toxins are named for Kiyoshi Shiga, who first described the bacterial origin of dysentery caused by 2 (stx2) but not Shiga toxin 1 (stx1); approximately 30% of E. coli O157 isolates sent to CDC since 1983 expressed only stx2. From July through September 2000, six states (California, Michigan, New Jersey, New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of , Ohio, and Texas) reported a total of 64 E. coli O157 isolates with PulseNet pattern EXHX01.0047, a value that exceeded expectation for this time of year and that prompted an epidemiologic investigation. Not all of these patterns were submitted to CDC's central database for confirmation. Fifty-one of these isolates were probed for Shiga toxin genes, and all possessed only stx2. Illness onsets ranged from April 1 through August 21, 2000, with a notable increase after late May 2000. The median age of case-patients was 13 years (range 1-91), and 38 (60%) were female; 36 (57%) of 64 were hospitalized, and hemolytic uremic syndrome hemolytic uremic syndrome
A syndrome in which hemolytic anemia and thrombocytopenia occur with acute renal failure, marked in children by sudden gastrointestinal bleeding, urine that contains red blood cells and is scanty in volume, and developed in 9 (14%).
To determine the source of these E. coli O157:H7 infections, six state health departments (California, Michigan, New Jersey, New York, Ohio, and Texas) and CDC initiated an epidemiologic investigation. Informed consent was obtained from all patients or their parents or guardians and human experimentation Human experimentation involves medical experiments performed on human beings. It is an important part of medical research, and many people volunteer for clinical trials of medical treatments. People also volunteer to be subjects for experiments in basic medical science and biology. guidelines of the U.S. Department of Health and Human Services Noun 1. Department of Health and Human Services - the United States federal department that administers all federal programs dealing with health and welfare; created in 1979
Health and Human Services, HHS were followed. These data were collected as part of an outbreak investigation and therefore were exempt from formal institutional review board aprovals.
Through hypothesis-generating interviews with 19 infected persons, 11 food exposures were reported by [greater than or equal to] 50% of interviewees or were reported in substantial excess relative to that food's frequency of consumption in the general population (4). In a case-control study case-control study,
n an investigation employing an epidemiologic approach in which previously existing incidents of a medical condition are used in lieu of gathering new information from a randomized population. that used a survey instrument that focused on these 11 food exposures, controls were matched to case-patients by sex and age group, and were asked about exposures during the same 5-day period before the matching case-patient's illness onset. Controls were contacted and identified by using sequential-digit dialing beginning with the matching patient's telephone number.
Twenty-eight case-patients and 69 matched controls were enrolled (2.46 controls per patient). The median age was 13.5 years and 50% were female; case-patients did not differ significantly from controls in terms of sex or age. In matched univariate analysis by using logistic regression In statistics, logistic regression is a regression model for binomially distributed response/dependent variables. It is useful for modeling the probability of an event occurring as a function of other factors. with stratification (LogXact version 2.1.1, Cytel Software Corporation, Cambridge, MA), only broccoli was significantly associated with illness (matched odds ratio [mOR] 3.65, p = 0.04); 14 (58%) of 24 case-patients, and 19 (31%) of 62 controls reported eating broccoli. Although none of the three foods that contained ground beef were individually associated with illness, consumption of "any hamburger" (a composite variable) was significant (mOR 7.30, p = 0.01), reported by 20 (87%) of 23 patients and 28 (55%) of 51 controls. In multivariate analysis multivariate analysis,
n a statistical approach used to evaluate multiple variables.
n a set of techniques used when variation in several variables has to be studied simultaneously. , only eating "any hamburger" remained significantly associated with illness (OR = 6.13, p = 0.02).
Ground beef eaten by case-patients was recovered from three households; samples from two households (in New Jersey and California) yielded E. coli O157:H7 isolates that were indistinguishable from PulseNet pattern EXHX01.0047. One of these isolates was tested for Shiga toxin and produced only stx2. Using information from these two cases and additional information regarding likely ground beef sources for the original Michigan cases, the U.S. Department of Agriculture performed a traceback; however, an extensive investigation did not identify any common supplier for the two samples of ground beef.
We performed a retrospective review retrospective review,
a posttreatment assessment of services on a case-by-case or aggregate basis after the services have been performed. of available isolate patterns received by the PulseNet national database after the case-control study and traceback had been completed. Four additional states (Florida, Indiana, Massachusetts, and Washington) had reported E. coli O157 isolates with XbaI patterns that were indistinguishable from PulseNet pattern EXHX01.0047. Among the 46 submitted XbaI patterns from states reporting a possible match to PulseNet pattern EXHX01.0047, analysis at CDC indicated that 38 were indistinguishable and that 6 differed by one band from the PulseNet pattern EXHX01.0047 (Figure 1). Furthermore, among the 38 isolates confirmed as PulseNet pattern EXHX01.0047, digestion of 13 isolates with the restriction enzyme restriction enzyme
Protein (more specifically, an endonuclease) produced by bacteria that cleaves DNA at specific sites along its length. Thousands have been found, from many different bacteria; each recognizes a specific nucleotide sequence. BlnI produced PFGE patterns that sorted into multiple distinct clusters (Figure 2).
[FIGURES 1-2 OMITTED]
Identifying outbreaks of E. coli O157:H7 infections by routinely subtyping isolates using PFGE is a relatively new phenomenon (2,3). Traditionally, PFGE has been used to support or refute the likelihood of epidemiologic relatedness among case-patients and suspect food vehicles in epidemiologic investigations. In this instance, the converse occurred; the results of routine PFGE subtyping (XbaI) of E. coli O157:H7 isolates prompted a large, multistate epidemiologic investigation. Isolates were potentially related because 1) the PFGE patterns obtained with one restriction enzyme (XbaI) were reported to be indistinguishable and a relatively uncommon pattern, and 2) the isolates shared a Shiga toxin profile that was relatively uncommon among E. coli O157 (stx2 only). A rigorous case-control study implicated im·pli·cate
tr.v. im·pli·cat·ed, im·pli·cat·ing, im·pli·cates
1. To involve or connect intimately or incriminatingly: evidence that implicates others in the plot.
2. a widely consumed food vehicle responsible for multiple past outbreaks of E. coli O157 infections: ground beef (5). This study and the isolation of two E. coli O157 with matching PFGE patterns from ground beef consumed by case-patients prompted two extensive traceback investigations. However, no common source could be identified. Subsequent digestion of patient isolates with a second enzyme showed that they were actually part of multiple, small clusters and that the illnesses were thus unlikely to be related to a common source.
Investigation of suspected multistate outbreaks requires substantial public health resources (6). This investigation involved more than 50 federal, state, and local staff. E. coli O157:H7 infections can cause serious and potentially life-threatening illness that may also engender legal action. Public health authorities must ensure that linkage
of illnesses to an outbreak be as complete and accurate as possible. Rapid identification of the infections' source can avert many potential illnesses. Earlier studies demonstrated the value of subtyping E. coli O157:H7 isolates with two or more restriction endonuclease digestions or using other subtyping methods, such as phage phage: see bacteriophage.
phage - A program that modifies other programs or databases in unauthorised ways; especially one that propagates a virus or Trojan horse. See also worm, mockingbird. The analogy, of course, is with phage viruses in biology. typing, to determine whether such isolates are truly related, even if these isolates have produced matching patterns using a single enzyme digestion (7-9). More recently, in the absence of epidemiologic data, single enzyme PFGE has been found to be a poor measure of genetic relatedness (10). Since 1998, the PulseNet Task Force has recommended the use of at least two enzyme digestions for optimal subtyping of E. coli O157 isolates. However, because of resource limitations, many state and local public health laboratories initially subtype E. coli O157 isolates with XbaI enzyme and perform subtyping with a second enzyme only if clusters are identified and personnel and resources are in place to do so. This investigation lends further support to the conclusion that when clusters of E. coli O157 are detected on the basis of subtyping data only (i.e., in the absence of any epidemiologic data), digestion with two or more endonucleases is warranted, even if the isolates appear to share a primary enzyme pattern or possess other microbiologic evidence of clonality (e.g., Shiga toxin profile). Furthermore, these findings underscore the importance of having a centralized database team that can rapidly verify reports of clusters from participating PulseNet laboratories and assist in determining whether isolates are likely to be part of an outbreak and whether a rapid, large-scale epidemiologic investigation and traceback would be warranted.
We acknowledge the many people at CDC, USDA USDA,
n.pr See United States Department of Agriculture. , and state and local health departments who contributed their time and efforts to this investigation. We especially thank Keith Pilot, Sylvia Matiuk, Maria Lidicker, Dianna J. Schoonmaker-Bopp, Deborah Shea, Jeffrey Higa, and Sharon Abbott Sharon Abbott (nee' Collins) also known as Sharon Newman is a fictional character in the CBS soap opera, The Young and the Restless, played by actress Sharon Case since 1994. .
Funding or support was provided by CDC's Emerging Infections Programs and Food Safety Office.
Dr. Gupta is currently at Johns Hopkins University Johns Hopkins University, mainly at Baltimore, Md. Johns Hopkins in 1867 had a group of his associates incorporated as the trustees of a university and a hospital, endowing each with $3.5 million. Daniel C. , Division of Infectious Diseases infectious diseases: see communicable diseases. . Her research interests include enteric enteric /en·ter·ic/ (en-ter´ik) within or pertaining to the small intestine.
1. Of, relating to, or within the intestine.
2. diseases and HIV HIV (Human Immunodeficiency Virus), either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS. There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States. clinical care and treatment research in India.
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(2.) Swaminathan B, Barrett TJ, Hunter SB, Tauxe RV. PulseNet: the molecular subtyping network for foodborne bacterial disease A bacterial disease is an abnormal condition of an organism (disease) caused by bacteria, a type of unicellular microorganisms. Not all bacteria cause disease, and not all diseases are caused by bacteria, or even microorganisms. surveillance, United States. Emerg Infect Dis. 2001;7:382-9.
(3.) Bender JB, Hedberg CW, Besser JM, Boxrud D J, MacDonald KL, Osterholm MT. Surveillance by molecular subtype for Escherichia coli O157:H7 infections in Minnesota by molecular subtyping. N Engl J Med. 1997;337:388-44.
(4.) Centers for Disease Control and Prevention. Foodborne Diseases Active Surveillance Network (FoodNet): population survey atlas of exposures: 1998-2000. Atlanta: The Centers; 2000.
(5.) Slutsker L, Ries AA, Greene KD, Wells JG, Hutwagner L, Griffin PM. Escherichia coli O157:H7 diarrhea in the United States: clinical and epidemiologic features. Ann Intern Med. 1997;126:505-13.
(6.) Elbasha EH, Fitzsimmons TD, Meltzer MI. Costs and benefits of a subtype-specific surveillance system for identifying Escherichia coli O157:H7 outbreaks. Emerg infect Dis. 2000;6:293-7.
(7). Barrett TJ, Lior H, Green JH, Khakhria R, Wells JG, Bell BP, et al. Laboratory investigation of a multistate food-borne outbreak of Escherichia coli O157:H7 by using pulsed-field gel electrophoresis and phage typing. J Clin Microbiol. 1994;32:3013-7.
(8.) Proctor ME, Kurzynski T, Koschmann C, Archer JR, Davis JP. Four strains of Escherichia coli O157:H7 isolated from patients during an outbreak of disease associated with ground beef: importance of evaluating multiple colonies from an outbreak-associated product. J Clin Microbiol. 2002;40:1530-3.
(9.) Preston MA, Johnson W, Khakhria R, Borczyk A. Epidemiologic subtyping of Escherichia coli serogroup O157 strains isolated in Ontario by phage typing and pulsed-field gel electrophoresis. J Clin Microbiol. 2000;38:2366-8.
(10.) Davis MA, Hancock DD, Besser TE, Call DR. Evaluation of pulsed-field gel electrophoresis as a tool for determining the degree of genetic relatedness between strains of Escherichia coli O157:H7. J Clin Microbiol. 2003;41:1843-9.
Address for correspondence: Amita Gupta: Johns Hopkins University, Division of Infectious Diseases, 1830 East Monument Street, Room 450E, Baltimore, MD 21287, USA; fax 410-614-8488; email: agupta25@ jhmi.edu
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