An Epidemic, Toxin Gene–Variant Strain of Clostridium difficile L. Clifford McDonald, M.D., George E. Killgore, Dr.P.H., Angela Thompson, M.M.Sc., Robert C. Owens, Jr., Pharm.D., Sophia V. Kazakova, M.D., M.P.H., Ph.D., Susan P. Sambol, M.T., Stuart Johnson, M.D., and Dale N. Gerding, M.D.
b a c k g r o u n d
Recent reports suggest that the rate and severity of Clostridium difficile–associated disease From the Epidemiology and Laboratory Branch, Division of Healthcare Quality Pro- in the United States are increasing and that the increase may be associated with the motion, Centers for Disease Control and emergence of a new strain of C. difficile with increased virulence, resistance, or both.
Prevention, Atlanta (L.C.M., G.E.K., A.T.,S.V.K.); the Departments of Pharmacy andInfectious Diseases, Maine Medical Cen- ter, Portland (R.C.O.); the College of Med- A total of 187 C. difficile isolates were collected from eight health care facilities in six states icine, University of Vermont, Burlington(Georgia, Illinois, Maine, New Jersey, Oregon, and Pennsylvania) in which outbreaks (R.C.O.); and the Infectious Disease Sec- of C. difficile–associated disease had occurred between 2000 and 2003. The isolates Medicine, Hines Veterans Affairs Hospital were characterized by restriction-endonuclease analysis (REA), pulsed-field gel electro- and Loyola University Stritch School ofphoresis (PFGE), and toxinotyping, and the results were compared with those from a Medicine, Hines, Ill. (S.P.S., S.J., D.N.G.).
database of more than 6000 isolates obtained before 2001. The polymerase chain reac- at 1600 Clifton Rd., MS A35, Atlanta, GA tion was used to detect the recently described binary toxin CDT and a deletion in the 30333, or at [email protected]
pathogenicity locus gene, tcdC, that might result in increased production of toxins A Copyright 2005 Massachusetts Medical Society. Isolates that belonged to one REA group (BI) and had the same PFGE type (NAP1) wereidentified in specimens collected from patients at all eight facilities and accounted forat least half of the isolates from five facilities. REA group BI, which was first identifiedin 1984, was uncommon among isolates from the historic database (14 cases). Both his-toric and current (obtained since 2001) BI/NAP1 isolates were of toxinotype III, werepositive for the binary toxin CDT, and contained an 18-bp tcdC deletion. Resistance togatifloxacin and moxifloxacin was more common in current BI/NAP1 isolates than innon-BI/NAP1 isolates (100 percent vs. 42 percent, P<0.001), whereas the rate of resis-tance to clindamycin was the same in the two groups (79 percent). All of the current butnone of the historic BI/NAP1 isolates were resistant to gatifloxacin and moxifloxacin(P<0.001).
c o n c l u s i o n s
A previously uncommon strain of C. difficile with variations in toxin genes has becomemore resistant to fluoroquinolones and has emerged as a cause of geographically dis-persed outbreaks of C. difficile–associated disease.
Downloaded from www.nejm.org at UNIVERSITY OF CALGARY on December 5, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. The new england journal of medicine Diseases Society of America, which found that ap- positive, anaerobic, spore-forming bacillus proximately 39 percent of respondents noted an in- c that can cause pseudomembranous colitis crease in the severity of cases of C. difficile–associated and other C. difficile–associated diseases. Studies disease in their patient population.15during the 1970s showed that two toxins, A and B, One explanation for an increase in both the rate were involved in the pathogenesis of C. difficile–asso- and the severity of C. difficile–associated diseaseciated disease.1-5 Transmission occurs primarily in could be the emergence of an epidemic strain withhealth care facilities, where exposure to antimicro- increased virulence, antimicrobial resistance, orbial drugs (the major risk factor for C. difficile–asso- both. To examine this possibility, we characterizedciated disease) and environmental contamination C. difficile isolates obtained from health care facilitiesby C. difficile spores are more common.6 Certain that reported outbreaks from 2001 through 2003strains of C. difficile have a propensity to cause out- and compared these isolates with historic isolatesbreaks, including multistate outbreaks in health (obtained before 2001) with the use of strain typing,care facilities.7 Because these outbreak-associated identification of genetic determinants of newly de-strains are resistant to certain antimicrobial agents, scribed virulence factors, and testing for antimi-such as clindamycin, the use of such antimicrobial crobial susceptibility.
agents provides these strains with a selective advan-tage over strains that are not associated with out- breaks. Historically low rates of severe disease and
death (3 percent or less) may have led to an under- health care facilities and isolates
estimation of the importance of C. difficile–associ- from patients
ated disease as a health care–associated infection8; Isolates were collected from patients in eight health
however, each case of C. difficile–associated disease care facilities that had reported an outbreak of
has been estimated to result in more than $3,600 in C. difficile–associated disease since 2001 to investi-
excess health care costs, and these costs may exceed gators at either the CDC or the Hines Veterans Af-
$1 billion annually in the United States.9
fairs (VA) Hospital. These facilities were located Both the rate and the severity of C. difficile–asso- in six states (Georgia, Illinois, Maine, New Jersey, ciated disease may be increasing in U.S. health care Oregon, and Pennsylvania); all were acute care hos-facilities. An analysis of data from the National pitals, except for one long-term care facility inNosocomial Infections Surveillance system identi- Georgia that was associated with a VA hospital.16fied an upward slope in C. difficile–associated dis- The isolates were obtained from patients who hadease rates from the late 1980s through 2001.10 Of received a diagnosis of C. difficile–associated diseasegreater concern is a reported increase of 26 percent- on the basis of clinical history (e.g., diarrhea withage points between 2000 and 2001 in the propor- recent receipt of an antimicrobial drug) and a posi-tion of patients discharged from nonfederal U.S. tive clinical laboratory test for C. difficile toxin (e.g.,hospitals with C. difficile–associated disease listed cytotoxin assay or enzyme immunoassay). Isolatesas a diagnosis.11 from current (since 2001) outbreaks were compared Indications of the increased severity of C. difficile– with isolates from a historic (pre-2001) database of associated disease include reports from the Univer- more than 6000 C. difficile isolates maintained by
sity of Pittsburgh Medical Center, where the inci- Hines VA investigators. The isolates in the historic
dence of the disease in 2000 and 2001 was nearly database were collected during the period from
twice as high as in 1990 through 1999. Twenty-six 1984 through 1990; all isolates were extensively
patients with severe disease required colectomy, and characterized by HindIII restriction-endonuclease
18 patients died.12-14 In addition, in the past two analysis (REA) and linked to clinical and epidemio-
years, the Centers for Disease Control and Preven- logic data.
tion (CDC) has received an increased number of
reports from health care facilities of cases of severe strain typing
C. difficile–associated disease that have resulted in ad- The isolates underwent REA typing and pulsed-
missions to intensive care units, colectomies, and field gel electrophoresis (PFGE), as previously de-
deaths. These reports have been confirmed by a na- scribed17,18; software from BioNumerics 3.5 (Ap-
tionwide survey of infectious-disease physicians in plied Maths) was used to perform dendrographic
the Emerging Infections Network of the Infectious analysis of the PFGE results. In addition, toxino-
Downloaded from www.nejm.org at UNIVERSITY OF CALGARY on December 5, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved.
a n e p i d e m i c , t o x i n g e n e – v a r i a n t s t r a i n o f c l o s t r i d i u m d i f f i c i l e typing was performed according to the method ofRupnik et al., with modifications.19 Toxinotyping analyzes the restriction-fragment–length polymor- phisms (RFLPs) of the genes encoding toxins A (tcdA) and B (tcdB), the surrounding regulatory genes(tcdC and tcdD), and a porin gene (tcdE) in a region of the C. difficile genome known as the pathogenicitylocus (PaLoc) (Fig. 1). Because RFLP analysis of polymerase-chain-reaction (PCR) fragments A3 andB1 results in a pattern sufficient to identify most Figure 1. Major Genes in the Pathogenicity Locus (PaLoc) of Clostridium
toxinotypes,19 we limited our analysis to these two difficile and Relation to the Genes for Binary Toxin.
Genes tcdA and tcdB encode toxins A and B, respectively, whereas tcdD encodes a positive regulator of the production of toxins A and B. Gene tcdE encodes a protein that may be important for the release of toxin from the cell. Gene tcdC m o l e c u l a r m a r k e r s o f p o t e n t i a l l y
is a putative negative regulator of the production of toxins A and B. Genes i n c r e a s e d v i r u l e n c e
cdtA and cdtB are located at an unknown distance from the PaLoc and encode In addition to the well-characterized A and B toxins, the enzymatic and binding components, respectively, of binary toxin. B1 and a binary toxin has been identified in about 6 percent A3 designate the location and relative size of the gene fragments that under- of clinical C. difficile isolates obtained in the United went polymerase-chain-reaction (PCR) amplification for toxinotyping.
States and Europe.20,21 The structure and functionof this toxin (referred to as binary toxin CDT) aresimilar to those of other binary toxins, such as the Standards Institute (CLSI; formerly the Nationaliota toxin found in C. perfringens, and it is a suspect- Committee for Clinical Laboratory Standards).25ed virulence factor in strains of C. difficile that carry However, because no breakpoints have been set bythe toxin.22 We detected the C. difficile binary toxin the CLSI for C. difficile tested against these fluoro-gene by using PCR for cdtB, which is located outside quinolones, the CLSI breakpoints for C. difficile test-the PaLoc and encodes the beta subunit of the binary ed against trovafloxacin were used. The validity oftoxin (Fig. 1).20 the trovafloxacin breakpoints was confirmed by We also looked for deletions in tcdC by using identification of two distinct subpopulations in the PCR with the primers tcdc1 and tcdc2, which were distribution of minimum inhibitory concentrations
synthesized at the CDC Core Facility on the basis of (MICs) for apparently susceptible isolates, as com-
published sequences.23 The gene tcdC is located pared with resistant isolates, tested against these
within the PaLoc downstream from the genes en- fluoroquinolones; these subpopulations were de-
coding toxins A and B, and it is transcribed in the marcated by the trovafloxacin breakpoints. Quality
opposite direction from these genes (Fig. 1). The control of antimicrobial-susceptibility testing was
tcdC protein is thought to function as a negative performed during each test run with the standard
regulator of the production of toxins A and B. Re- strains Enterococcus faecalis American Type Culture
cently, multiple alleles of tcdC have been described Collection (ATCC) 29212, Pseudomonas aeruginosa
that include different-sized deletions, point muta- ATCC 27583, Bacteroides fragilis ATCC 25285, and
tions, and in one case, a nonsense mutation, all of B. thetaiotaomicron ATCC 29741.
which would result in a truncated tcdC protein.23,24
It has been hypothesized that mutations in tcdC may statistical analysis
result in a loss of negative regulatory function, lead- To compare the overall resistance patterns of cur-
ing to increased toxin production and virulence.23,24 rent epidemic and nonepidemic isolates, a total of
three (determined according to the availability of t e s t i n g f o r a n t i m i c r o b i a l s u s c e p t i b i l i t y
isolates) epidemic-strain (case) and three nonepi- Susceptibility to clindamycin and the fluoroquino- demic-strain (control) isolates, as determined bylones (levofloxacin, gatifloxacin, and moxifloxacin) REA and PFGE, were randomly selected from eachwas determined with the use of E-test strips (AB health care facility. Resistance was then comparedBiodisk), and the results were interpreted accord- by matched case–control analysis with the use ofing to standard criteria.25 Specific breakpoints for Epi Info software (version 6.02). This method wasthe interpretation of clindamycin-susceptibility re- chosen to take into account possible geographicsults were available from the Clinical and Laboratory variation in resistance and to avoid bias resulting Downloaded from www.nejm.org at UNIVERSITY OF CALGARY on December 5, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved.
The new england journal of medicine from outbreaks with a larger number of isolates. In netic testing, along with three BI/NAP1 and threecontrast, we used Fisher’s exact test and the Stat- non-BI/NAP1 current isolates from each health careCalc function of Epi Info software (version 6.02) to facility. The PFGE results and the dendrogram ofmake an unmatched comparison between current these representative isolates are shown in Figure 2,and historic epidemic isolates. All P values are based along with the toxinotype, the status of binaryon a two-tailed comparison.
CDT, and the status of a deletion in the tcdC gene.
According to dendrographic analysis, 25 of 29 ofthe combined current and historic BI/NAP1 isolates (86 percent) were 90 percent or more related, and A total of 187 isolates were obtained from the eight all were more than 80 percent related. In contrasthealth care facilities in which the outbreaks oc- to this close relatedness among BI/NAP1 isolatescurred. In each of the facilities, a strain composed across a wide geographic area, relatively few non-of closely related isolates was identified by both BI/NAP1 isolates were more than 80 percent relat-PFGE and REA. This epidemic strain accounted for ed. All of the BI/NAP1 isolates were of toxinotype50 percent or more of the isolates from five of the III, were positive for binary toxin CDT, and had aneight facilities (Table 1). The epidemic strain has 18-bp deletion in tcdC; these features were largelybeen identified as belonging to REA group BI and absent among non-BI/NAP1 isolates (Fig. 2). Of theNorth American PFGE type 1 (NAP1). Within this 24 non-BI/NAP1 isolates, 20 (83 percent) were tox-strain, characterized as BI/NAP1, the isolates have inotype 0, none of which had binary toxin CDT orbeen further differentiated on the basis of minor the tcdC deletion.
differences in the band pattern into 14 REA sub- Susceptibility testing was performed on the 3 cur- types, designated by numbers, in which at least 90 rent BI/NAP1 and non-BI/NAP1 isolates from eachpercent of the bands are identical.17 Similarly, sev- health care facility, as well as on the 14 patient BIeral PFGE subtypes are included in the NAP1 desig- isolates available from the historic database. Amongnation. Five REA BI types (BI1 through BI5), dating current isolates (obtained after 2000), all BI/NAP1back to 1984, were identified in the historic data- and only a fraction of the non-BI/NAP1 isolates werebase. These represented 18 isolates obtained from resistant to gatifloxacin and moxifloxacin (Table 2).
14 patients and consisted of 5 isolates of BI1 from Although both BI/NAP1 and non-BI/NAP1 isolates4 patients, 8 isolates of BI2 from 7 patients, 2 iso- were largely resistant to clindamycin and levo-lates of BI3 from 1 patient, 2 isolates of BI4 from floxacin, the MICs of levofloxacin were higher for1 patient, and 1 isolate of BI5 from 1 patient.
BI/NAP1 isolates as a group (Fig. 3). All current One isolate from each of the five REA BI types in BI/NAP1 isolates and no historic isolates (obtained the historic database was selected for further ge- before 2001) were resistant to gatifloxacin and mox- Table 1. Isolates of Clostridium difficile According to Health Care Facility
and the Proportion of Isolates Belonging to the BI/NAP1 Strain.
Date of Onset No. of Isolates
An epidemic strain of C. difficile has been associated Health Care Facility
of Outbreak
BI/NAP1 Strain
with outbreaks of C. difficile–associated disease in eight health care facilities since 2001. This strain is the same as the strain responsible for recent outbreaks outside the United States.26,27 It is clas- sified by REA typing as BI and by PFGE as NAP1, and is distinct from the J strain (REA type J7/9) thatwas responsible for outbreaks during the period from 1989 through 1992.28 Eighteen related isolates of the BI REA group, obtained from 14 known U.S.
cases of C. difficile–associated disease that occurred between 1984 and 1993, were found in a database of more than 6000 isolates (representing more than100 REA groups). According to PFGE dendrograph- * Isolates were not collected until after the peak of the outbreak.
ic analysis, the majority of BI/NAP1 strain isolates Downloaded from www.nejm.org at UNIVERSITY OF CALGARY on December 5, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved.
a n e p i d e m i c , t o x i n g e n e – v a r i a n t s t r a i n o f c l o s t r i d i u m d i f f i c i l e Relatedness (%)
18-bp tcdC
Binary CDT
Figure 2. Pulsed-Field Gel Electrophoresis Results and Dendrographic Analysis of a Sample of BI/NAP1 and Non-BI/NAP1 Isolates
from Current Outbreaks of Clostridium difficile
–Associated Disease and of Isolates from a Historic Database.
The years listed for the historic isolates indicate years in which isolates of that type were recovered from patients, according to the database. The asterisk denotes the presence of a 39-bp deletion in tcdC.
Downloaded from www.nejm.org at UNIVERSITY OF CALGARY on December 5, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. The new england journal of medicine Table 2. Resistance of Current BI/NAP1 Clostridium difficile Isolates, Current Non-BI/NAP1 Isolates, and Historic BI/NAP1 Isolates
to Clindamycin and Fluoroquinolones.*

Current BI/NAP1 Isolates Current Non-BI/NAP1 Isolates
Historic BI/NAP1 Isolates
no. with intermediate resistance or resistant (%)§ no. with intermediate resistance or resistant (%) * The fluoroquinolones are levofloxacin, moxifloxacin, and gatifloxacin. Current BI/NAP1 isolates are those obtained since 2001, and historic BI/NAP1 isolates are those obtained before 2001.
† The P value is for the comparison between BI/NAP1 and non-BI/NAP1 isolates.
‡ The P value is for the comparison between current and historic BI/NAP1 isolates.
§ A minimal inhibitory concentration breakpoint of not more than 2 µg per milliliter was used for the definition of susceptibility, on the basis of the recommendations of the Clinical Laboratory Standards Institute for trovafloxacin.
(including historic BI isolates) were more than 90 C. difficile–associated disease, may have an impor-percent related, and all were more than 80 percent tant role in the causation of severe disease.
related. Although current BI/NAP1 isolates shared The importance of binary toxin CDT as a viru- with historic BI isolates the putative virulence fac- lence factor in C. difficile has not been established;tors of binary toxin and an 18-bp deletion in tcdC, however, a similar toxin, iota toxin, is responsiblethe current isolates were more likely to be resistant for virulence in C. perfringens.22 In previous reports,to fluoroquinolones. Therefore, the increasing use binary toxin CDT was found in only about 6 percentof fluoroquinolones in U.S. health care facilities may of C. difficile isolates20,21,31; therefore, our findinghave provided a selective advantage for this epidem- that the prevalence of this toxin is much higher inic strain and promoted its widespread emergence.
isolates from outbreaks associated with increased The most compelling evidence of an increase in morbidity suggests that it could, indeed, affect the the severity of C. difficile–associated disease in the severity of C. difficile–associated disease. PreviousUnited States is found in the reports from Pennsyl- studies have indicated that C. difficile strains with bi-vania Facility A, where an increase in both the num- nary toxin CDT nearly always have polymorphismsber of cases and the severity of the disease was noted in the PaLoc.21 Binary toxin CDT has been associat-in 2000 and 2001.12-14 In addition, there was evi- ed with several different toxinotype patterns31; indence of higher white-cell counts and more severe our isolates, it was associated with toxinotype III,disease in patients infected with BI/NAP1 strains which was infrequently found in previous clinicalthan in those infected with non-BI/NAP1 strains at surveys. Pseudomembranous colitis is more fre-the Illinois facility in our study.29 Another report quent among patients infected with C. difficile offrom a Connecticut hospital indicates an increase toxinotype III than among patients infected within the number of cases of severe disease necessitat- C. difficile of other toxinotypes, suggesting that thising colectomy during a recent outbreak associat- toxinotype is associated with increased severity ofed with the BI/NAP1 strain.30 However, reports of the disease.19,21other outbreaks, such as the outbreak in the Georgia The importance of the 18-bp deletion in tcdC is long-term care facility included in our study, do not currently unknown. Although tcdC is a proposedsuggest increased disease severity.16 Even in the negative regulator of the production of toxins Acase of Pennsylvania Facility A, investigators were and B, it is not known whether this 18-bp deletionunable to find a significant association between the would render a tcdC product nonfunctional andoccurrence of severe C. difficile–associated disease lead to increased production of toxins A and B.23,24and infection with the outbreak strain (P=0.23).14 A recent report, however, indicates that BI/NAP1Therefore, other factors, such as underlying host isolates in vitro do, indeed, produce toxins A and Bsusceptibility, prevailing practices of the use of anti- in considerably greater quantities and at highermicrobial agents or approaches to the treatment of rates than non-BI/NAP1 isolates.27 Nonetheless, Downloaded from www.nejm.org at UNIVERSITY OF CALGARY on December 5, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. a n e p i d e m i c , t o x i n g e n e – v a r i a n t s t r a i n o f c l o s t r i d i u m d i f f i c i l e additional research on the effects of binary toxinCDT and of tcdC deletions on the severity of C. diffi- cile–associated disease appears warranted.
In addition to geographic variation in disease severity, there is variation in the role of particular fluoroquinolones as risk factors in these outbreaks.
The outbreak in the Georgia long-term care facility occurred after a change in the formulary from levo-floxacin to a C-8-methoxy fluoroquinolone, gati- No. of Isolates
floxacin.16 Gatifloxacin was an important riskfactor for C. difficile–associated disease among pa- tients, and the outbreak resolved after a formularyswitch back to levofloxacin. The authors hypothe- sized that the higher antianaerobic activity of gati- Minimum Inhibitory Concentration (µg/ml)
floxacin than of levofloxacin led to a greater alter-ation in bowel flora and that this, combined withresistance to fluoroquinolone in the prevailing C. dif- Figure 3. Distribution of Minimum Inhibitory Concentrations of Levofloxacin
for Current (Obtained after 2000) BI/NAP1 and Non-BI/NAP1 Clostridium

ficile strain, contributed to the outbreak.16 difficile Isolates.
Similarly, in Pennsylvania Facility B, the outbreak started within three months after a switch in theformulary from levofloxacin to a C-8-methoxy fluo- patient.33 Enhanced environmental cleaning withroquinolone (moxifloxacin); the preliminary results dilute bleach should be used to eliminate C. difficileof a case–control study identify moxifloxacin as a spores.34 Because alcohol is ineffective in killingrisk factor for C. difficile–associated disease during C. difficile spores, it is prudent for health care work-the outbreak.32 In Pennsylvania Facility A, C. difficile– ers to wash their hands with soap and water, ratherassociated disease was associated with the use of than with alcohol-based waterless hand sanitizers,levofloxacin, clindamycin, and ceftriaxone.13 How- when caring for patients with C. difficile–associatedever, a higher proportion of cases of C. difficile–asso- disease during an outbreak.35 ciated disease was associated with levofloxacin (31 Finally, an important method of controlling past percent) than with clindamycin (10 percent) or cef- outbreaks of C. difficile–associated disease has beentriaxone (7 percent).
restriction of the use of antimicrobial agents impli- The emergence of a previously uncommon strain cated as risk factors for the disease.36 Whether a of C. difficile that is more resistant and potentially large-scale restriction of the use of these antimi-more virulent than other strains indicates a need crobial agents could slow the geographic spread offor inpatient health care facilities in North America the BI/NAP1 strain is not known. Because fluoro-to track the incidence of C. difficile–associated dis- quinolones have become a mainstay in the treat-ease. Clinical outcomes of patients with C. difficile– ment of several common infections, a large-scaleassociated disease should also be monitored, espe- restriction of the use of these drugs would be quitecially if an increase in rates is noted. If an increase difficult. However, if this epidemic strain continuesin the proportion of severe cases is noted, special to spread and to contribute to increased morbidityconsideration should be given to the need for early and mortality, it will be important either to recon-diagnosis and treatment. Strict infection-control sider the use of fluoroquinolones or to developmeasures, including contact precautions, should be other innovative measures for controlling C. difficile–instituted for all patients with C. difficile–associated associated disease.
disease. In contact precautions, the patient is placed Supported in part by grants from the Department of Veterans Af- in a room alone or with another patient with C. dif- fairs Research Service (to Drs. Johnson and Gerding).
Presented in part at the 42nd Annual Meeting of the Infectious ficile–associated disease, health care workers wear Diseases Society of America, Boston, October 1–3, 2004.
gloves and gowns when entering the room, and Dr. Owens reports having received research funding from Elan, patient-care equipment (such as blood-pressure Bayer, Ortho-McNeil, and Pfizer; Dr. Johnson, research funding from Salix Pharmaceuticals and consulting fees or fees for service on an cuffs and stethoscopes) either is used only for the advisory board from Genzyme, Acambis, ViroPharma, and Salixpatient or is cleaned before it is used for another Pharmaceuticals; and Dr. Gerding, research funding from Presutti Downloaded from www.nejm.org at UNIVERSITY OF CALGARY on December 5, 2005 . Copyright 2005 Massachusetts Medical Society. All rights reserved. The new england journal of medicine Laboratories, ActivBiotics, Oscient Pharmaceuticals, and Optimer sisting in the characterization and analysis of isolates: Jemelae Pharmaceuticals and consulting fees or fees for serving on an advi- Bessette, Priscilla Biller, Adam Cheknis, Robert Gaynes, Carol Gen- sory board from Acambis, Oscient Pharmaceuticals, ViroPharma, ese, Kathleen Gensheimer, David Gilbert, Lee Harrison, Bette Jensen, Genzyme, Optimer Pharmaceuticals, and Salix Pharmaceuticals. Dr.
Susan Kohlhepp, James Martin, Linda McDougal, Michelle Merrigan, Gerding holds U.S., Canadian, and European Union patents for the Carlene Muto, Gary Noskin, Sandra Reiner, Corey Robertson, Kath- use of nontoxigenic C. difficile to treat and prevent C. difficile infection.
leen Roye-Horn, Steve Sears, Farida Siddiqui, Sarah Slaughter, Lisa We are indebted to the members of the Clostridium difficile Investi- Tkatch, Marty Topiel, August J. Valenti, Carol Ward, Kim Ware, John gation Team for making isolates available for study or otherwise as- Warren, Lois Wiggs, Teresa Zembower, and Walter Zukowski.
r e f e r e n c e s
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Source: http://clubs.ucalgary.ca/~ngk/carbo/cdiff/NEJM_CDC_dec8_05.pdf

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