US Pharm. 2006;6:52-60.

Clostridium difficile is an anaerobic, gram-positive, spore- and toxin-producing bacillus that was first discovered in 1935. At that time, it was considered to be normal flora in neonates, and the organism¡¯s role in antibiotic-associated diarrhea was not elucidated until the 1970s.1 Since then, C. difficile ¨Cassociated diarrhea (CDAD) has become one of the most common and problematic nosocomial infections to contain. Recently, the pathophysiology and epidemiology of CDAD have been changing. Noteworthy developments include reports of more severe CDAD, cases occurring in settings not associated with health care, and a potential reduction in treatment effectiveness. This article will provide a brief review of traditional CDAD, as well as summarize the recent noteworthy changes in disease that pharmacists should recognize.

Background
The classic intestinal manifestations of CDAD consist of three or more episodes of watery diarrhea per day, fever, leukocytosis, and abdominal pain or cramping.2 While diarrhea is the most common manifestation, CDAD symptoms can range all the way from asymptomatic carriage to severe disease characterized by pseudomembranous colitis, toxic megacolon, colonic perforation, and death. In pseudomembranous colitis, the colonic mucosa is studded with raised white and yellowish plaques that may coalesce to form pseudomembranes (composed of mucin, neutrophils, fibrin, and cellular debris) that can exist throughout the entire colon. Toxin-secreting C. difficile is associated with 10% to 30% of cases of antibiotic-associated diarrhea, 50% to 70% of cases of antibiotic-associated colitis, and greater than 90% of cases of antibiotic-associated pseudomembranous colitis.2-4

The development of CDAD is a multistep process that involves alteration of normal colonic flora by antibacterial agents, colonization by and overgrowth of toxin-secreting isolates of C. difficile, and subsequent expression of toxin, which leads to mucosal injury and inflammation. Normal gut flora confers protection against infection with C. difficile, as animal models suggest that normally present gut bacteria limit carbon sources required for C. difficile overgrowth.4 Prior antibacterial use traditionally predisposes a person to development of CDAD, as it disrupts the normal gut flora. In most cases, alteration of normal flora precedes colonization of the colon via the fecal¨Coral route. The acid-resistant C. difficile spores enable the organism to pass through the acidic medium of the stomach unharmed. In the duodenum, they are exposed to primary bile acid necessary for the conversion to vegetative forms. It should be noted that alteration of normal colonic flora does not always precede colonization with C. difficile via the fecal¨Coral route. Many pediatric and adult patients have been identified as asymptomatic carriers. When CDAD develops in such cases, it is often due to overgrowth of resistant C. difficile subsequent to selection by antibacterial use. As C. difficile multiplies, it produces two toxins (A and B) that cause diarrhea and colitis. The two toxins are internalized by intestinal epithelium and ultimately cause cytoskeletal disruption, cell rounding and retraction, opening of tight junctions of intestinal epithelial cells, and apoptosis. Toxins A and B also induce inflammation and secretory responses via various inflammatory mediators and neutrophil chemotaxis.3,4

Most cases of CDAD have been associated with nosocomial transmission. Surveillance studies have shown that 20% to 30% of hospitalized patients typically become colonized with C. difficile, with approximately one third proceeding to develop CDAD.2,4 Historically, there have been reports of CDAD being associated with community-acquired diarrhea as well; however, in most cases these patients had recent previous exposure to health care resources (e.g., hospitalization or nursing home).5 Health care worker hand carriage with transfer from patient to patient likely accounts for the majority of nosocomial transmission. Contact with contaminated fomites (e.g., telephones, bedpans, rectal thermometers) has been implicated in the spread of C. difficile as well. Further, despite environmental cleaning, the persistence of spores for weeks to months after a patient has left the environment also contributes to horizontal transmission.5

Classic risk factors for developing CDAD include hospitalization, advanced age, chronic comorbidity, gastrointestinal surgery or manipulations, tube feedings, use of anti-acid drugs (particularly proton pump inhibitors), and preeminently, previous exposure to antimicrobial agents (including antineoplastic agents with antimicrobial activity).5-11 While virtually all antimicrobials have been associated with development of CDAD, agents such as clindamycin, aminopenicillins, and cephalosporins historically have been considered to pose the greatest risk.4,5,8,12 This strong association of CDAD with the use of certain antibiotics is due to selection of resistant C. difficile . In many epidemics of CDAD, the circulating clone was found to be resistant to antibiotics that were considered to be risk factors for the outbreak, such as clindamycin.12 Subsequent reduction in the use of the antibiotic identified as selecting resistant C. difficile resulted in a decrease in CDAD.13

Pharmacotherapy of CDAD
Treatment of CDAD generally includes the administration of oral metronidazole or vancomycin. If possible, the offending antibiotic should be discontinued. In severe disease, colonoscopy and surgical intervention may be necessary. Studies conducted during the late 1970s and 1980s found similar clinical cure rates between metronidazole and vancomycin, ranging from 86% to 98%.14 Due to concerns about the potential for oral vancomycin to foster the development of vancomycin-resistant Enterococcus and the equivalence of the two agents in clinical trials, national guidelines published during the 1990s recommended oral metronidazole as the agent of choice and vancomycin use only in cases of metronidazole failure or severe or life-threatening disease.5 The recommended dosing for metronidazole is 250 mg QID or 500 mg TID for 10 days. Oral vancomycin is typically dosed at 125 mg QID for 10 days. Metronidazole and vancomycin regimens are generally well tolerated.2 The most common adverse effects of metronidazole therapy include a disulfiram-like reaction, if alcohol is used concurrently, and loss of appetite or taste disturbance.

Changing Prevalence of CDAD
The prevalence rate of CDAD has changed notably since the 1970s. An analysis of hospital data from the National Nosocomial Infectious Surveillance System identified an upward trend in rates of CDAD from the mid to late 1980s to 2001.15 More recently, CDAD rates have increased with greater intensity. From 2000 to 2001, rates of CDAD on U.S. hospital discharge diagnoses increased by 26% (figure 1). 16 One locale, the University of Pittsburgh Medical Center¨CPresbyterian, reported that the incidence of CDAD in 2000 and 2001 was nearly double the incidence from 1990 to 1999.17 In Quebec, rates almost quadrupled, from 35.6 to 156.3 per 100,000 population.18

Historically, the prevalence of CDAD in outpatient populations has been low, with the overall risk assessed at less than one case per 10,000 outpatient prescriptions for antibiotics.19 In May and June of 2005, 23 cases of community-acquired CDAD (CA-CDAD) were reported from Pennsylvania, Ohio, New Hampshire, and New Jersey.19 The cases occurred in patients thought to be at low risk (no or low exposure to a health care setting) for CDAD. The estimated annual incidence in Philadelphia and surrounding areas was 7.6 cases per 100,000 population, and one case per 5,549 antibiotic prescriptions. The increase in prevalence rates of CDAD in both the nosocomial and community setting appear to correspond with the widespread emergence of a previously uncommon strain of C. difficile termed BI/NAP1 (figure 2). 20



The Emergence of the C. difficile BI/NAP1 Strain

McDonald et al. recently published findings on 187 C. difficile isolates collected from health care facilities with CDAD outbreaks in eight states between 2000 and 2003.21 Molecular analysis was used to compare these strains to more than 6,000 isolates collected prior to 2001. The BI/NAP1 strain was determined to constitute one half of the 2000¨C2003 isolates, whereas this strain was identified in only 17% of the historical isolate collection. The BI/NAP1 strain contains a different toxin called binary toxin. While the specific role of binary toxin as a virulence factor is unknown and under investigation, isolates that contain the gene for binary toxin also frequently were missing a gene (tcdC) that serves as a negative regulator for production of classic C. difficile toxins A and B. BI/NAP1 isolates have been shown to produce 16 and 23 times more A and B toxins in vitro, respectively, than have previous epidemic strains.22 It is important to note that while binary toxin itself has not been established as a virulence factor, researchers noted that the prevalence of the binary toxin was higher in isolates from outbreaks associated with increased morbidity, including those hospitals reported by McDonald.21

Changing Severity of Disease
There are now numerous reports of both increasing severity of CDAD and increased attributable mortality since 2001.17-19,21,23,24 In 2002 in Quebec, complicated cases (defined as death within 30 days, megacolon, perforation, colectomy, or shock requiring vasopressors) increased fourfold over rates among historical controls dating back to 1989.23 Thirty-day mortality also increased from 4.7% to 13.8% during the same study period. In 2000¨C2001, the epidemic at University of Pittsburgh Medical Center¨CPresbyterian reported a doubling in life-threatening CDAD infections, identifying 64 patients who required colectomies or died of CDAD.17,25 Typically, historical reports of attributable mortality due to CDAD have been <3%. However, several studies have recently reported attributable mortality as high as 16.7% and overall mortality as high as 37%.17,18,23,24 The CA-CDAD cases described above also had a 30% overall hospitalization rate and included reports of severe CDAD, including death.19

Changing Antibiotic Risk Factors Associated with CDAD
Paralleling the emergence of the BI/NAP1 C. difficile strain, fluoroquinolones are increasingly being implicated as risk factors for development of CDAD. 25-28 In some cases, older fluoroquinolones such as ciprofloxacin and levofloxacin have been implicated; however, several reports of association of CDAD with gatifloxacin and moxifloxacin, which possess antianaerobic activity, are concerning.26,28 Analysis of antimicrobial spectra may partially explain this association as both moxifloxacin and gatifloxacin possess greater anaerobic activity than levofloxacin and ciprofloxacin, thus incurring greater disruption of colonic flora and a subsequent increase in the likelihood of developing CDAD. Gaynes et al., analyzing a CDAD outbreak in a Veterans Affairs (VA) long-term-care facility, reported a sharp increase in CDAD after a formulary conversion from levofloxacin to gatifloxacin.26 Use of gatifloxacin, as well as of clindamycin, was highly correlated with CDAD. The outbreak terminated upon a formulary change back to levofloxacin. The previously reported outbreaks in Quebec and in Pittsburgh also reported that certain fluoroquinolones, as well as select cephalosporins and clindamycin, were associated with CDAD.25,28 In the Quebec outbreak, Pepin and colleagues reported that patients given gatifloxacin versus other fluoroquinolones were at greater risk for CDAD.28 Further, fluoroquinolone administration for as short as one to three days was associated with CDAD, whereas most other antibiotics associated with increased risk of CDAD required more than three days. Finally, the aforementioned McDonald study reported that resistance to gatifloxacin and moxifloxacin was virtually 100% in BI/NAP1 isolates compared to 42% of non¨CBI/NAP1 isolates. 21 Seventy-nine percent of both groups of isolates were resistant to clindamycin. In summary, fluoroquinolones have emerged as strong risk factors for the development of CDAD, especially disease caused by the BI/NAP1 strains, and newer fluoroquinolones with antianaerobic activity may pose the greatest risk.

Potentially Decreased Effectiveness of CDAD Treatment
Treatment of CDAD has not changed appreciably in the past 25 years. In the early 1980s, oral vancomycin was considered the standard of care, with a response rate approximating 80% to 90%. Metronidazole was also shown to be comparably efficacious. Due to concerns about oral vancomycin use increasing risk for vancomycin-resistant Enterococcus spread, metronidazole became the agent of choice for most cases of CDAD.5 In the past five years, concern has surfaced over the efficacy of the current treatment modalities. The aforementioned study from Quebec posted alarming treatment failure rates, suggesting problems with efficacy of metronidazole: Use of vancomycin as a ¡°rescue¡± therapy remained at 9.6% from 1991 to 2002 but increased by more than twofold to 25.7% in 2003 to 2004.23 In addition, the recurrence rate of patients treated with metronidazole increased from 20.8% to 47.2% during the same period. Further analysis tempers the reports of alarming recurrence rates. Researchers discovered that of the 463 patients who experienced a first recurrence of CDAD, most subsequent infections were reinfections rather than relapses.29 In addition, neither metronidazole nor vancomycin was associated with a higher recurrence rate or more severe initial disease. However, in patients with advanced age, WBC ¡Ý 20,000 and serum creatinine ¡Ý2.2 mg/dL were associated with complicated CDAD, irrespective of treatment. Another study from a Texas VA hospital also suggested the efficacy of metronidazole to be approximately 50%, markedly different from the 90% reported in the 1980s.30

Reasons for the apparent lack of efficacy of current treatment modalities are not clear. Few in vitro studies have suggested that the minimum inhibitory concentration of metronidazole for C. difficile is higher in some strains; however, susceptibility data for metronidazole and vancomycin were not reported for the Quebec and Texas VA studies.14 In addition, no evidence exists indicating that metronidazole resistance plays a clinically important role in treatment failures and recurrence. Gerding suggested that the variability in clinical failure rates in the aforementioned studies may be related to the observational nature and differences in case definitions and clinical end points.31 In addition, the highly virulent strains identified may have factors that predispose infected individuals to relapses of CDAD. Finally, the highly virulent strains of C. difficile may lengthen hospitalization and thus increase the risk of becoming reinfected and redeveloping CDAD.29 In summary, while there are several recent reports of increasing clinical failures and relapses, it is unclear if these findings represent loss of antibiotic potency, increased disease virulence, or differences in clinical reporting methods between trials. However, the clinician should be aware of the possibility of increased CDAD treatment failures with standard therapies.

Potential Impact on Diagnosis, Prevention, and Treatment
The emergence of increasingly severe CDAD has several implications for its diagnosis and treatment. First, for patients (both inpatients and outpatients) who develop diarrhea and have any risk factors for CDAD, early diagnosis and treatment are critical to prevent morbidity and mortality. Pharmacists in both hospital and community settings are capable of contributing to early diagnosis and treatment, as they are aware of risk factors (especially antibiotic risk factors). In a community setting, pharmacists often receive requests from patients who seek nonprescription products for relief of diarrhea. Pharmacists should inquire about recent antibiotic use by the patient or the immediate family members (siblings, etc.) as part of the patient assessment and should consider referral for further medical evaluation if CDAD risk and symptoms are present. Patients with CDAD should not receive antimotility antidiarrheal agents, such as loperamide or diphenoxylate, as these may worsen CDAD.2

Prevention and control of CDAD are vital in all patient care settings. All patients being treated for CDAD and their caregivers should be reminded to wash their hands regularly with soap and warm water.32 It is important to note that the use of alcohol-based disinfecting hand rub solutions are not recommended, as the solutions are not reliably sporicidal and will not prevent spread of C. difficile spores as well as traditional hand washing. Cleaning and disinfection of environmental surfaces (e.g., bedpans, light switches, bathtubs) are also recommended, since C. difficile spores may last for weeks to months. Various disinfecting agents, such as unbuffered hypochlorite or formaldehyde and glutaraldehyde, have been employed, and further study is merited to determine which disinfectants are most effective. While environmental disinfection practices are standard in institutional settings, a 10% bleach solution is affordable, is readily prepared at home, and is an effective disinfectant for household use. Given the aggressive nature of BI/NAP1 C. difficile strains and the recent reports of CA-CDAD, it is prudent to recommend these practices to outpatients being treated for CDAD and to their caregivers.

Since asymptomatic carriers harbor C. difficile, some clinicians have attempted to eliminate asymptomatic carriage by administration of metronidazole or vancomycin. Due to metronidazole¡¯s virtually complete absorption by those without diarrhea, it is ineffective in eliminating asymptomatic carriage, as intraluminal concentrations are negligible.33 Further, while oral vancomycin eliminates carriage effectively (due to high fecal concentrations even during normal gut motility), recolonization with C. difficile is common in patients. Given these findings, use of metronidazole or vancomycin for prevention by eliminating asymptomatic carriage is not recommended.5

Antimicrobial therapy has been identified as the preeminent risk factor for the development of CDAD, and restriction of certain antibiotics has been shown to interrupt epidemics. Various studies at hospitals throughout the U.S. have shown that restriction of clindamycin decreased the incidence of CDAD associated with clindamycin-resistant epidemic strains.13 The emergence of CDAD caused by fluoroquinolones may necessitate similar restriction of fluoroquinolone use, at least during CDAD epidemics.26 Use of antimicrobials that possess lower risk for developing CDAD than do gatifloxacin and moxifloxacin (cotrimoxazole, tetracyclines, macrolides, etc.) may be preferable for the treatment of many uncomplicated infections, particularly in outpatients without recent antibiotic exposure. Pharmacists are encouraged to discuss these options for treatment with patients and health care providers, when appropriate.




The most recent reports from Quebec tend to support the current Standard of Care, which suggests that initial or first recurrences of mild to moderate CDAD be treated with metronidazole, with vancomycin reserved for severe or refractory disease.5,29 In such cases, use of oral vancomycin seems prudent if the patient¡¯s condition continues to deteriorate or WBC counts rise after metronidazole is started. 31 In addition, increased monitoring of metronidazole efficacy in such cases may be necessary to detect treatment failure or sequelae of C. difficile infection. Further, development of ileus or fulminant CDAD may require surgery, in addition to more aggressive treatment such as intravenous metronidazole coupled with vancomycin enemas.13 Recurrent CDAD is a problem for which no clear consensus has emerged. Repeating treatment courses with high-dose vancomycin has proven efficacious, while others employ pulsed dosing, believing that C. difficile spores will germinate between pulses and be susceptible to the next dose of drug.34,35

Conclusion
In the past five years, the pathophysiology and epidemiology of CDAD have changed. Noteworthy developments include reports of more severe CDAD, cases occurring in settings not associated with health care, and a potential reduction in treatment effectiveness. table 1 highlights the take-home points to remember about the recent findings involving CDAD. The changing nature of CDAD presents new challenges for patient care in which effective drug therapy is necessary, and a number of new antibiotic as well as nonantibiotic therapies are in development. As professionals versed in drug therapy, pharmacists are positioned to contribute to effective patient care by evaluating patient risk for CDAD and providing recommendations regarding prevention and effective drug therapy for all severities of CDAD.

References
1. Tedesco FJ, Barton RW, Alpers DH. Clindamycin-associated colitis: a prospective study. Ann Intern Med. 1974;81:429-433.
2. Thielman NM, Wilson KH. Antibiotic-associated colitis. In: Mandell, Douglas, and Bennett¡¯s Principles and Practice of Infectious Diseases. Philadelphia: Elsevier Churchill Livingstone; 2005:1249-1259.
3. Mylonakis E, Ryan ET, Calderwood SB. Clostridium difficile¨Cassociated diarrhea: a review. Arch Intern Med. 2001;161:525-533.
4. Bartlett JG. Clinical practice: antibiotic-associated diarrhea. N Engl J Med. 1996;346:334-339.
5. Gerding DN, Johnson S, Peterson L, et al. Clostridium difficile¨Cassociated diarrhea and colitis. SHEA Position Paper. Infect Control Hosp Epidemiol. 1995;16:459-477.
6. Manabe YC, Vinetz JM, Moore RD, et al. Clostridium difficile colitis: an efficient approach to diagnosis. Ann Intern Med. 1995;123:835-840.
7. Bliss DZ, Johnson S, Savik K, et al. Acquisition of Clostridium difficile and Clostridium difficile-associated diarrhea in hospitalized patients receiving tube feeding. Ann Intern Med. 1998;129:1012-1019.
8. Oldfield EC 3rd. Clostridium difficile-associated diarrhea: risk factors, diagnostic methods, and treatment. Rev Gastroenterol Disord. 2004;4:186-195.
9. Kyne L, Sougioultzis S, McFarland LV, Kelly CP. Underlying disease severity as a major risk factor for nosocomial Clostridium difficile diarrhea. Infect Control Hosp Epidemiol . 2002;23:653-659.
10. Dial S, Alrasadi K, Manoukian C, et al. Risk of Clostridium difficile diarrhea among hospital inpatients prescribed proton pump inhibitors: cohort and case-control studies. CMAJ. 2004;171:33-38.
11. 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;294:2989-2995.
12. 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;341:1645-1651.
13. Davey P, Brown E, Fenelon L, et al. Interventions to improve antibiotic prescribing practices for hospital inpatients. Cochrane Database Syst Rev. 2005;(4):CD003543.
14. Aslam S, Hamill RJ, Musher DM. Treatment of Clostridium difficile-associated disease: old therapies and new strategies. Lancet Infect Dis. 2005;5:549-557.
15. Archibald LK, Banerjee SN, Jarvis WR. Secular trends in hospital-acquired Clostridium difficile disease in the United States, 1987¨C2001. J Infect Dis. 2004;189:1585-1589.
16. McDonald CL, Owings M, Jernigan DB. Clostridium difficile infection in patients discharged from US short-stay hospitals, 1996¨C2003. Emerg Infect Dis. 2006;12(3). Available from www.cdc.gov/ncidod/EID/vol12no03/05-1064.htm.
17. Dallal RM, Harbrecht BG, Boujoukas AJ, et al. Fulminant Clostridium difficile: an underappreciated and increasing cause of death and complications. Ann Surg . 2002;235:363-372.
18. Pepin J, Valiquette L, Alary ME, et al. Clostridium difficile-associated diarrhea in a region of Quebec from 1991 to 2003: a changing pattern of disease severity. CMAJ. 2004;171:466-472.
19. Centers for Disease Control and Prevention (CDC). Severe Clostridium difficile-associated disease in populations previously at low risk¡ªfour states, 2005. MMWR Morb Mortal Wkly Rep. 2005;54:1201-1205.
20. Centers for Disease Control and Prevention. Clostridium difficile Infections. Available at: www.cdc.gov/ncidod/dhqp/id_Cdiff_data.html. Accessed February 15, 2006.
21. McDonald LC, Killgore GE, Thompson A, et al. An epidemic, toxin gene-variant strain of Clostridium difficile. N Engl J Med. 2005;353:2433-2441.
22. Bartlett JG, Perl TM. The new Clostridium difficile¡ªwhat does it mean? N Engl J Med . 2005;353:2503-2505.
23. 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;40:1591-1597.
24. Pepin J, Valiquette L, Cossette B. Mortality attributable to nosocomial Clostridium difficile-associated disease during an epidemic caused by a hypervirulent strain in Quebec. CMAJ. 2005;173:1037-1042.
25. 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;26:273-280.
26. 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;38:640-645.
27. McCusker ME, Harris AD, Perencevich E, Roghmann MC. Fluoroquinolone use and Clostridium difficile-associated diarrhea. Emerg Infect Dis. 2003;9:730-733.
28. 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;41:1254-1260.
29. Pepin J, Routhier S, Gagnon S, Brazeau I. Management and outcomes of a first recurrence of Clostridium difficile-associated disease in Quebec, Canada. Clin Infect Dis . 2006;42:758-764.
30. Musher DM, Aslam S, Logan N, et al. Relatively poor outcome after treatment of Clostridium difficile colitis with metronidazole. Clin Infect Dis. 2005;40:1586-1525.
31. Gerding DN. Metronidazole for Clostridium difficile-associated disease: is it okay for Mom? Clin Infect Dis. 2005;40:1598-1600.
32. Boyce JM, Pittet, D. Guideline for hand hygiene in health-care settings. MMWR Recomm Rep. 2002;51(RR16):1-45.
33. Johnson S, Homann SR, Betin KM, et al. Treatment of asymptomatic Clostridium difficile carriers (fecal excretors) with vancomycin or metronidazole. Ann Intern Med. 1992;117:297-302.
34. Tedesco FJ, Gordon D, Fortson WC. Approach to patients with multiple relapses of antibiotic-associated pseudomembranous colitis. Am J Gastroenterol. 1985;80:867-868.
35. McFarland LV, Elmer GW, Surawicz CM. Breaking the cycle: treatment strategies for 163 cases of recurrent Clostridium difficile disease. Am J Gastroenterol. 2002;97:1769-1775.

To comment on this article, contact editor@uspharmacist.com.