The Challenges Posed by Reemerging Clostridium difficile Infection

Transcription

1 EMERGING INFECTIONS James M. Hughes and Mary E. Wilson, Section Editors INVITED ARTICLE The Challenges Posed by Reemerging Clostridium difficile Infection David B. Blossom and L. Clifford McDonald Division of Healthcare Quality Promotion, National Center for Preparedness, Detection, and Control of Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia There have been recent, marked increases in the incidence and severity of Clostridium difficile associated disease (CDAD). These may be attributable to the emergence of a hypervirulent strain of C. difficile that produces increased levels of toxins A and B, as well as an extra toxin known as binary toxin. This previously uncommon strain has become epidemic, coincident with its development of increased resistance to fluoroquinolones, the use of which is increasingly associated with CDAD outbreaks. Although not necessarily related to this epidemic strain, unusually severe CDAD has been reported in populations that had previously been thought to be at low risk, including peripartum women and healthy persons living in the community. Challenges posed by the changing epidemiology of CDAD are compounded by current limitations in diagnostic testing, treatment, and infection control. Overcoming these challenges and limitations will require a concerted effort from a variety of sources, including an ongoing partnership between infectious disease clinicians and public health professionals. BACKGROUND Clostridium difficile, a gram-positive, spore-forming, toxin-producing bacillus, was first described in 1935 as a component of the intestinal flora in healthy newborn infants. The role of C. difficile in human disease was not appreciated until the 1970s, when it was identified as the causative agent of pseudomembranous colitis [1]. Additional studies demonstrated that C. difficile associated disease (CDAD) encompasses a range of disease severity from colitis (which, in many cases, manifests only as diarrhea) to toxic megacolon (which can result in sepsis and even death). C. difficile is the most commonly identified cause of antibiotic-associated diarrhea, accounting for 15% 25% of cases [2]. A typical presentation involves an older patient with frequent, loose, watery stools who has been recently treated with a course of antimicrobials while hospitalized for a chronic medical condition. Because most patients experience no complications [3], many clinicians have, in the past, viewed CDAD as more of a nuisance or a side effect of antimicrobial use, Received 11 January 2007; accepted 9 March 2007; electronically published 4 June The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the Centers for Disease Control and Prevention. Reprints or correspondence: Dr. L. Clifford McDonald, 1600 Clifton Rd., MS A35, Atlanta, GA (cmcdonald1@cdc.gov). Clinical Infectious Diseases 2007; 45:222 7 This article is in the public domain, and no copyright is claimed /2007/ $15.00 DOI: / rather than focusing on it as a disease entity. Regardless, the financial burden of the disease has always been significant. One study in the 1990s revealed that, even though CDAD had a low attributable mortality rate (i.e.,!2%), it was costing US hospitals 1$1 billion annually to treat [4]. CHANGING EPIDEMIOLOGY IN HEALTH CARE SETTINGS Despite this history of CDAD as a relatively mild albeit costly health care associated infection, there have been alarming increases in both the incidence and severity of this disease reported over the past several years. An analysis of US hospital discharge data revealed that CDAD rates increased abruptly beginning in 2001, with a doubling of national rates from 2000 through 2003 [5]. This increase was most prominent for patients aged 164 years, among whom the rates are highest (figure 1), and it occurred in all geographic regions. Regional outbreaks of more-severe disease, resulting in increased deaths and in colectomies performed to avert death, date back to the year The earliest report was in Pittsburgh, Pennsylvania [6]; other outbreaks soon followed in Quebec, Canada [7], and the Centers for Disease Control and Prevention (CDC) initially began hearing about outbreaks of severe CDAD from hospitals in the mid-atlantic and southeastern United States [8]. On the basis of data from Quebec, the attributable mortality rate for CDAD increased to 6.9% [7]. 222 CID 2007:45 (15 July) EMERGING INFECTIONS

2 Figure 1. Rates of discharges from US short-term stay hospitals of patients with Clostridium difficile associated disease listed as any diagnosis, by age [5]. EMERGENCE OF AN EPIDEMIC STRAIN Growing evidence suggests the emergence of a hypervirulent, epidemic strain as an important factor in the recent increases in CDAD incidence and severity. In both Quebec hospitals and hospitals in multiple locations in the United States, a previously uncommon strain of C. difficile was found to be the epidemic strain and to be responsible for multiple, near-simultaneous outbreaks of hospital infection [7, 8]. Not only has this strain been identified in 24 states (as of March 2007), it has also been identified as causing outbreaks in the United Kingdom and in parts of continental Europe, suggesting it is now a global epidemic strain [9]. It is characterized as North American Pulsed Field Type 1 (NAP1), restriction enzyme analysis type BI, and PCR ribotype 027 [8, 10]. NAP1/BI/027 can also be characterized via restriction enzyme analysis of the toxin and surrounding regulatory genes as toxinotype III, a previously uncommon toxinotype; historically, 180% of hospital strains were toxinotype 0 [11]. In addition to the large clostridial toxins A and B, which are the main recognized virulence factors of C. difficile, NAP1/BI/ 027 possesses an extra toxin known as binary toxin. This toxin, which is related to the iota-toxin found in Clostridium perfringens, was first discovered in C. difficile in 1988 [12] and, until recently, was found in 6% of isolates recovered from hospitalized patients [11]. Although studies are underway, the role of binary toxin in human CDAD remains unknown [13]. In addition, NAP1/BI/027 possesses an 18 base pair deletion [7, 8] and a frameshift mutation leading to a premature stop codon [14] in tcdc, a putative negative regulator of toxin A and B production. This may be important, because NAP1/BI/027 has been shown to produce 16-fold more toxin A and 23-fold more toxin B in vitro [10]. Whether it is binary toxin, increased toxin A and B production, or other unidentified virulence factors that are responsible, NAP1/BI/027 does appear to produce more-severe disease than other strains [7, 15]. Increased virulence alone, however, does not explain how a previously uncommon strain has recently become epidemic; historic isolates of NAP1/BI/027 from nearly 25 years ago possess the same binary toxin genes and deletions in tcdc as contemporary isolates [8]. One factor that has changed is an increase in resistance to fluoroquinolones. Not only are contemporary isolates of NAP1/BI/027 more resistant to fluoroquinolones than are historic isolates of this same strain, they are also more resistant than contemporary, nonepidemic strain isolates [8, 16]. The concept of a particular C. difficile strain becoming an epidemic strain on the basis of a selective advantage afforded by increased resistance to a particular antimicrobial was previously observed in the late 1980s and early 1990s with the highly clindamycin-resistant J strain [17]. DISEASE IN PREVIOUSLY LOW-RISK POPULATIONS In addition to disease in health care settings, C. difficile can cause disease in healthy individuals. In 2005, the CDC reported the occurrence of severe CDAD in several peripartum women and persons living in the community [18]. Although severe peripartum disease is still uncommon, the CDC is aware of cases of CDAD in this population that have resulted in colectomy or death. Previous reports of community-associated CDAD (CA-CDAD) from the United States suggested that CA- CDAD was very uncommon [19]; however, studies performed in Sweden 5 10 years ago suggested that as many as 1 in 5 cases of CDAD may be CA-CDAD [20]. In addition, some patients with CA-CDAD may not have a history of recent antimicrobial use [18, 21], which, if confirmed, could change our understanding of C. difficile as a human pathogen. Thus far, there is little information about the strains responsible for CA- CDAD or the sources of these strains. EMERGING RISK FACTORS Antimicrobial therapy is the most widely recognized risk factor for CDAD; these drugs are thought to act through the disruption of the normal bowel flora, providing a niche for C. difficile to multiply and elaborate toxins. Although virtually all antimicrobial agents have been implicated in the development of CDAD, some recent studies of CDAD caused by the current NAP1/BI/027 strain have found that fluoroquinolones were the antimicrobials most closely associated with disease [6, 22]. In addition, increased duration of antimicrobial therapy, the use of broad-spectrum antimicrobials, and the use of multiple agents all contribute to the incidence of CDAD [23]. Another recently described risk factor that remains controversial is the use of stomach acid suppressing medications, such as proton pump inhibitors. Although some reports have refuted the role EMERGING INFECTIONS CID 2007:45 (15 July) 223

3 of these drugs [24, 25], others have suggested that proton pump inhibitors are particularly important in CA-CDAD and contribute to an apparent increase in the rate of CDAD among patients without precedent antimicrobial use [21, 26]. New exposure to C. difficile, especially in the hospital setting, where both the environment and the hands of health care workers easily become contaminated with spores from other patients, also plays an important role in the spread of disease. Unlike other multidrug-resistant organisms, the risk of developing CDAD is decreased, rather than increased, in hospitalized patients who are already colonized with C. difficile [27]. This may be due to a boosting in serum antitoxin antibody levels observed in these patients [28]. However, protection is also observed in both humans and animal models when colonization occurs with nontoxigenic strains [27, 29], suggesting there may be a role for the colonizing strain to occupy a microbial niche in the large intestine and to protect against superinfection with a new toxigenic strain. Regardless of the mechanism of protection, it is the patient who is newly exposed to C. difficile, rather than the patient who is already colonized with C. difficile, who is at increased risk of developing CDAD during an inpatient stay at a health care facility. DIAGNOSTIC CHALLENGES Clinicians should maintain a high level of suspicion regarding any patient who is receiving or who has recently received antimicrobials and who presents with diarrhea. Because of the emergence of CA-CDAD, clinicians should also consider the disease in patients from the community who present with several days of diarrhea, even without a history of antimicrobial exposure, provided that diagnostic tests for other bacterial and protozoan pathogens are also performed and that the results are negative. In addition, C. difficile testing in the absence of diarrhea may be appropriate in certain circumstances in which an intestinal ileus is suspected. Although the tissue cytotoxic assay is considered to be the gold standard, this test requires technical expertise, and it takes at least 48 h before results are available. As a result, most clinical laboratories use EIAs, which are much easier to perform and which can provide results in as little as 2 h. However, the sensitivity of EIAs is lower (range, 60% 95%). Although specificity has not been traditionally viewed as a major issue with either the tissue cytotoxic assay or EIAs, it is possible that, if these tests are used in populations in which the prevalence is relatively low (e.g., patients without precedent antimicrobial use), their positive predictive value will be unacceptably low. Additional studies are needed to improve our understanding of the limitations of current, commonly used assays and to improve testing paradigms. An approach that is still used in some European laboratories but that has been abandoned in virtually all US hospital laboratories is the use of anaerobic culture for the C. difficile organism. Although the test is extremely sensitive [30], it fell out of favor because of the high level of work involved, the slow turnaround time, and the inability to differentiate toxinproducing strains from non toxin-producing strains. This last limitation has been addressed in some laboratories by performing a toxigenic culture, in which an EIA is used to determine whether a C. difficile isolate recovered from culture is a toxinproducing strain. At least 1 report suggests that a toxigenic culture may be significantly more sensitive than EIAs and tissue cytotoxic assays that directly use stool specimens [31]. In addition, at present, the only way to determine what strains are affecting patients in a hospital or region is to perform stool culture; the shift by laboratories away from culture has made it more difficult to understand the changing epidemiology of C. difficile. TREATMENT CHALLENGES For the first several years after C. difficile was recognized as a cause of antibiotic-associated diarrhea, oral vancomycin was considered to be the treatment of choice. By the early 1980s, results of studies suggested that oral metronidazole was therapeutically equivalent to oral vancomycin in the treatment of CDAD [32, 33]. The main attractions of metronidazole were that it was less expensive than vancomycin and that some experts thought that it was less likely to promote the spread of vancomycin-resistant enterococci. Although not approved by the US Food and Drug Administration for this indication, oral metronidazole became the drug of choice for initial CDAD therapy, with the caveat that oral vancomycin should be used in patients with the most severe forms of disease [34]. Recently, however, the initial treatment of CDAD has come under renewed scrutiny as failure rates for metronidazole used as initial therapy have been reported to be in the range of 16% 38% [35, 36]; these are much higher than metronidazole failure rates of 7% that were reported in the 1990s [37]. Although there are no reports from North America of in vitro resistance to metronidazole, there is ongoing debate regarding the appropriate first-line therapy for C. difficile infection. Because most cases of CDAD are still mild, metronidazole would appear to still be appropriate for the initial treatment of most patients; what is unresolved is where in the continuum of moderateto-severe disease should oral vancomycin become the preferred agent, and what are the most important clinical indicators (e.g., WBC count, abdominal tenderness, and elevated serum creatinine level) that should be used to differentiate severity? It is disconcerting that, after 30 years of dealing with CDAD, we remain limited to 2 medications (i.e., oral vancomycin and 224 CID 2007:45 (15 July) EMERGING INFECTIONS

4 metronidazole) for treatment. Fortunately, there are now a handful of agents being developed as new therapies for CDAD. Tolevamer, a C. difficile toxin binding resin, is the agent farthest along in the approval process among the agents that are being developed specifically for CDAD [38]. Other agents, such as rifaximin [39] and nitazoxanide [40], are already approved for other gastrointestinal infections and are currently being investigated as potential therapies for CDAD. Novel agents in earlier phases of development include monoclonal antibodies directed at toxins A and B [41] and a C. difficile vaccine [42]. Another treatment challenge is recurrent CDAD, which occurs in 20% of cases after initial successful therapy. Although recurrence can develop up to 2 months after the completion of therapy, most recurrences occur within the first 30 days, and at least one-half of all recurrences represent reinfection (i.e., with a new infecting strain) rather than relapse. Several risk factors for recurrence have been identified, including advanced age, increased elevation of the WBC count during initial illness, and antimicrobial use in the interim between initial treatment and the recurrence. Along with recent evidence of increased clinical failures with metronidazole, there is evidence suggesting an increased number of recurrences. Overall, the most important risk factor for recurrence is recurrence itself; patients with at least 1 episode of recurrent CDAD have a 50% 65% chance of experiencing additional episodes [43]. Patients who develop multiple recurrences may be especially difficult to treat. One of the most common therapeutic techniques is to attempt a tapering of the vancomycin dose over several weeks, with decreasing doses or pulsed doses at the end of that taper. This highlights the problem with using an antimicrobial to treat a disease originally caused by the use of an antimicrobial: a patient s lower intestinal flora remains disturbed after discontinuing use of the antimicrobial directed at CDAD; it is at this point that CDAD is most likely to recur. Whether dosage tapering or pulsed dosing allows some restoration of normal flora while still suppressing C. difficile is unknown, but it does appear to have some efficacy in preventing recurrence. Although many have hoped that a specific probiotic could help fill the microbial void in the large intestine, either during or after antimicrobial therapy, few data support the use of these probiotics in the treatment of either initial or recurrent CDAD [44]. However, human stool transplants, either via enema or feeding tube, have shown some promise in treating patients with multiple recurrences of CDAD and for whom a variety of other regimens have failed [45]. PREVENTION CHALLENGES Because inpatient health care facilities remain at the epicenter of C. difficile transmission, there are several strategies that infection-control programs should use to prevent patient-to-patient transmission of C. difficile. First, contact precautions should be used for all patients with known CDAD [46]; these should include placement of the patient in a single room while he or she has diarrhea, with a bathroom used solely by that patient; alternatively, patients with CDAD may share the same room and bathroom (i.e., patient cohorting), provided that each is transferred out of the room once diarrhea ceases. In addition, gloves should be used by health care workers for all patient contact. Because alcohol does not eradicate C. difficile spores, there has been concern that widespread use of alcohol-based hand sanitizers for health care worker hand hygiene has had a role in recent increases in CDAD rates. However, there are data from a number of health care facilities demonstrating that overall CDAD rates tend to either decrease or remain the same after the introduction and increased use of alcohol-based sanitizers as the primary mode of hand hygiene in the care of all patients, including those with CDAD [47]. Nonetheless, if a health care facility is experiencing an outbreak of CDAD, it is prudent for health care workers to wash their hands with soap and water rather than using an alcohol-based hand sanitizer after glove removal [48]. Because C. difficile spores have the ability to survive on dry surfaces for several months, special attention needs to be given to environmental cleaning of care areas that accommodate patients with CDAD. At present, the only available products that are reliably sporicidal contain at least 5000 parts per million of sodium hypochlorite. This translates into a 1:10 dilution of household bleach that must be prepared fresh daily and that can be quite caustic and damage the surfaces of hospital equipment. Despite these drawbacks, use of such a solution should be considered for environmental cleaning of rooms and bathrooms used by patients with CDAD, especially in a facility that is experiencing an outbreak. Finally, major attention should be paid to controlling antimicrobial use. Targeted restriction of a particular antimicrobial agent or class of agents, such as clindamycin or third-generation cephalosporins, has led to control of individual hospital outbreaks or to reduced CDAD rates across hospitals [17, 49 50]. This was evident in the control of several outbreaks caused by the highly clindamycin-resistant J strain: clindamycin restrictions were followed by rapid reductions in CDAD cases [17]. Some have attempted, with varied success, individual restrictions of or formulary substitutions for fluoroquinolones during outbreaks caused by NAP1/BI/027 [22, 51]. However, it appears that fluoroquinolone resistance in NAP1/BI/027 strain is a class effect that is not limited to the newer 8-methoxyfluoroquinolones but that also results in higher MICs to all currently available fluoroquinolones [8, 16]. Thus, if any fluoroquinolone EMERGING INFECTIONS CID 2007:45 (15 July) 225

5 restriction is going to contribute to control, it is likely to be restriction or reduced use of all fluoroquinolones. FUTURE DIRECTIONS With the spread of NAP1/BI/027 throughout almost one-half of all US states, as well as much of Canada and western Europe, it is likely that rates of CDAD and associated morbidity and mortality will continue to increase before we see improvement. To reduce this morbidity and mortality, we will need advances in available treatments, therapeutic management strategies, and diagnostics. There will undoubtedly be new challenges presented by this organism as we improve our understanding of disease in previously low-risk populations and learn how C. difficile is transmitted in the community. To meet these challenges, it is clear that there will be an ongoing need for a coordinated and concerted effort on the part of clinicians, infection-control professionals, researchers, members of industry, and public health officials. Acknowledgments Potential conflicts of interest. References D.B.D. and L.C.M.: no conflicts. 1. Bartlett JG, Moon N, Chang TW, Taylor N, Onderdonk AB. Role of Clostridium difficile in antibiotic-associated pseudomembranous colitis. Gastroenterology 1978; 75: Bartlett JG. Antibiotic-associated diarrhea. Clin Infect Dis 1992; 15: Kelly CP, Pothoulakis C, Lamont JT. Clostridium difficile colitis. N Engl J Med 1994; 330: Kyne L, Hamel MB, Polavaram R, Kelly CP. Health care costs and mortality associated with nosocomial diarrhea due to Clostridium difficile. Clin Infect Dis 2002; 34: McDonald LC, Owings M, Jernigan D. Clostridium difficile infection in patients discharged from US short-stay hospitals, Emerg Infect Dis 2006; 12: Muto CA, Pokrywka M, Shutt K, et al. A large outbreak of Clostridium difficile-associated disease with an unexpected proportion of deaths and colectomies at a teaching hospital following increased fluoroquinolone use. Infect Control Hosp Epidemiol 2005; 26: Loo VG, Poirier L, Miller MA, et al. A predominantly clonal multiinstitutional outbreak of Clostridium difficile-associated diarrhea with high morbidity and mortality. N Engl J Med 2005; 353: McDonald LC, Killgore GE, Thompson A, et al. An epidemic, toxin gene-variant strain of Clostridium difficile. N Engl J Med 2005; 353: Kuijper EJ, Coignard B, Tull P. Emergence of Clostridium difficileassociated disease in North America and Europe. Clin Microbiol Infect 2006; 12(Suppl 6): Warny M, Pepin J, Fang A, et al. Toxin production by an emerging strain of Clostridium difficile associated with outbreaks of severe disease in North America and Europe. Lancet 2005; 366: Geric B, Rupnik M, Gerding DN, Grabnar M, Johnson S. Distribution of Clostridium difficile variant toxinotypes and strains with binary toxin genes among clinical isolates in an American hospital. J Med Microbiol 2004; 53: Popoff MR, Rubin EJ, Gill DM, Boquet P. Actin-specific ADP-ribosyltransferase produced by a Clostridium difficile strain. Infect Immun 1988; 56: Geric B, Carman RJ, Rupnik M, et al. Binary toxin-producing, large clostridial toxin-negative Clostridium difficile strains are enterotoxic but do not cause disease in hamsters. J Infect Dis 2006; 193: MacCannell DR, Louie TJ, Gregson DB, et al. Molecular analysis of Clostridium difficile PCR ribotype 027 isolates from Eastern and Western Canada. J Clin Microbiol 2006; 44: Hubert B, Loo VG, Bourgault AM, et al. A portrait of the geographic dissemination of the Clostridium difficile North American pulsed-field type 1 strain and the epidemiology of C. difficile associated disease in Quebec. Clin Infect Dis 2007; 44: Bourgault AM, Lamothe F, Loo VG, Poirier L. In vitro susceptibility of Clostridium difficile clinical isolates from a multi-institutional outbreak in Southern Quebec, Canada. Antimicrob Agents Chemother 2006; 50: Johnson S, Samore MH, Farrow KA, et al. Epidemics of diarrhea caused by a clindamycin-resistant strain of Clostridium difficile in four hospitals. N Engl J Med 1999; 341: Severe Clostridium difficile-associated disease in populations previously at low risk four states, MMWR Morb Mortal Wkly Rep 2005; 54: Hirschhorn LR, Trnka Y, Onderdonk A, Lee ML, Platt R. Epidemiology of community-acquired Clostridium difficile associated diarrhea. J Infect Dis 1994; 169: Noren T, Akerlund T, Back E, et al. Molecular epidemiology of hospitalassociated and community-acquired Clostridium difficile infection in a Swedish county. J Clin Microbiol 2004; 42: Dial S, Delaney JA, Barkun AN, Suissa S. Use of gastric acid-suppressive agents and the risk of community-acquired Clostridium difficile-associated disease. JAMA 2005; 294: Gaynes R, Rimland D, Killum E, et al. Outbreak of Clostridium difficile infection in a long-term care facility: association with gatifloxacin use. Clin Infect Dis 2004; 38: Bignardi GE. Risk factors for Clostridium difficile infection. J Hosp Infect 1998; 40: Pepin J, Saheb N, Coulombe MA, et al. Emergence of fluoroquinolones as the predominant risk factor for Clostridium difficile associated diarrhea: a cohort study during an epidemic in Quebec. Clin Infect Dis 2005; 41: Lowe DO, Mamdani MM, Kopp A, Low DE, Juurlink DN. Proton pump inhibitors and hospitalization for Clostridium difficile associated disease: a population-based study. Clin Infect Dis 2006; 43: Dial S, Delaney JA, Schneider V, Suissa S. Proton pump inhibitor use and risk of community-acquired Clostridium difficile-associated disease defined by prescription for oral vancomycin therapy. CMAJ 2006; 175: Shim JK, Johnson S, Samore MH, Bliss DZ, Gerding DN. Primary symptomless colonisation by Clostridium difficile and decreased risk of subsequent diarrhoea. Lancet 1998; 351: Kyne L, Warny M, Qamar A, Kelly CP. Asymptomatic carriage of Clostridium difficile and serum levels of IgG antibody against toxin A. N Engl J Med 2000; 342: Sambol SP, Merrigan MM, Tang JK, Johnson S, Gerding DN. Colonization for the prevention of Clostridium difficile disease in hamsters. J Infect Dis 2002; 186: Shanholtzer CJ, Willard KE, Holter JJ, Olson MM, Gerding DN, Peterson LR. Comparison of the VIDAS Clostridium difficile toxin A immunoassay with C. difficile culture and cytotoxin and latex tests. J Clin Microbiol 1992; 30: Delmee M, Van BJ, Simon A, Janssens M, Avesani V. Laboratory diagnosis of Clostridium difficile-associated diarrhoea: a plea for culture. J Med Microbiol 2005; 54: Cherry RD, Portnoy D, Jabbari M, Daly DS, Kinnear DG, Goresky CA. Metronidazole: an alternate therapy for antibiotic-associated colitis. Gastroenterology 1982; 82: Teasley DG, Gerding DN, Olson MM, et al. Prospective randomised trial of metronidazole versus vancomycin for Clostridium difficile-associated diarrhoea and colitis. Lancet 1983; 2: CID 2007:45 (15 July) EMERGING INFECTIONS

6 34. Centers for Disease Control and Prevention. Recommendations for preventing the spread of vancomycin resistance: recommendations of the Hospital Infection Control Practices Advisory Committee (HIC- PAC). MMWR Recomm Rep 1995; 44(RR-12): Musher DM, Aslam S, Logan N, et al. Relatively poor outcome after treatment of Clostridium difficile colitis with metronidazole. Clin Infect Dis 2005; 40: Pepin J, Alary ME, Valiquette L, et al. Increasing risk of relapse after treatment of Clostridium difficile colitis in Quebec, Canada. Clin Infect Dis 2005; 40: Olson MM, Shanholtzer CJ, Lee JT Jr, Gerding DN. Ten years of prospective Clostridium difficile-associated disease surveillance and treatment at the Minneapolis VA Medical Center, Infect Control Hosp Epidemiol 1994; 15: Louie TJ, Peppe J, Watt CK, et al. Tolevamer, a novel nonantibiotic polymer, compared with vancomycin in the treatment of mild to moderately severe Clostridium difficile associated diarrhea. Clin Infect Dis 2006; 43: Marchese A, Salerno A, Pesce A, Debbia EA, Schito GC. In vitro activity of rifaximin, metronidazole and vancomycin against Clostridium difficile and the rate of selection of spontaneously resistant mutants against representative anaerobic and aerobic bacteria, including ammonia-producing species. Chemotherapy 2000; 46: Musher DM, Logan N, Hamill RJ, et al. Nitazoxanide for the treatment of Clostridium difficile colitis. Clin Infect Dis 2006; 43: Babcock GJ, Broering TJ, Hernandez HJ, et al. Human monoclonal antibodies directed against toxins A and B prevent Clostridium difficileinduced mortality in hamsters. Infect Immun 2006; 74: Aboudola S, Kotloff KL, Kyne L, et al. Clostridium difficile vaccine and serum immunoglobulin G antibody response to toxin A. Infect Immun 2003; 71: McFarland LV. Alternative treatments for Clostridium difficile disease: what really works? J Med Microbiol 2005; 54: Dendukuri N, Costa V, McGregor M, Brophy JM. Probiotic therapy for the prevention and treatment of Clostridium difficile-associated diarrhea: a systematic review. CMAJ 2005; 173: Aas J, Gessert CE, Bakken JS. Recurrent Clostridium difficile colitis: case series involving 18 patients treated with donor stool administered via a nasogastric tube. Clin Infect Dis 2003; 36: Garner JS. Guideline for isolation precautions in hospitals. The Hospital Infection Control Practices Advisory Committee. Infect Control Hosp Epidemiol 1996; 17: Boyce JM, Ligi C, Kohan C, Dumigan D, Havill NL. Lack of association between the increased incidence of Clostridium difficile-associated disease and the increasing use of alcohol-based hand rubs. Infect Control Hosp Epidemiol 2006; 27: Boyce JM, Pittet D. Guideline for hand hygiene in health-care settings: recommendations of the Healthcare Infection Control Practices Advisory Committee and the HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. Infect Control Hosp Epidemiol 2002; 23(12 Suppl):S McNulty C, Logan M, Donald IP, et al. Successful control of Clostridium difficile infection in an elderly care unit through use of a restrictive antibiotic policy. J Antimicrob Chemother 1997; 40: Carling P, Fung T, Killion A, Terrin N, Barza M. Favorable impact of a multidisciplinary antibiotic management program conducted during 7 years. Infect Control Hosp Epidemiol 2003; 24: Biller P, Shank B, Lind L, et al. Moxifloxacin therapy as a risk factor of Clostridium difficile-associated disease during an outbreak: attempts to control a new epidemic strain. Infect Control Hosp Epidemiol 2007; 28: EMERGING INFECTIONS CID 2007:45 (15 July) 227