Clostridium difficile: an emerging infectious disease threat
Ines Prasidha BmedSci, MBBS (Hons)* |

*Medical Student, The University of Sydney

Abstract

Clostridium difficile (C. difficile) infection is the most common cause of nosocomial infection and antibiotic-associated diarrhoea, with high morbidity and mortality, causing extra costs and pressures on the Australian healthcare system. The organism is an obligate anaerobe, Gram positive bacillus that can exist in a vegetative or spore form and is transmitted by the faecal-oral route. The infection can range from asymptomatic colonisation to severe pseudomembranous colitis. C. difficile infection risk is increased by factors that impair the normal resistance mechanisms, particularly disruption of host flora by antibiotics. C. difficile infection is not notifiable to public health authorities in Australia and few data were available from Australia on the incidence of C. difficile infection and the distribution of the various ribotypes. This highlights the need for increased awareness and surveillance of C. difficile infection in Australia.

Introduction

WClostridium difficile is the most common cause of hospital-acquired and antibiotic-associated diarrhoea (1).  The infection can range from asymptomatic colonisation to severe pseudomembranous or fulminant colitis (2), resulting in prolonged hospital stays with high morbidity and mortality, and extra cost and pressure to the healthcare system (3).

In 2003, there has been an emergence of a highly virulent strain, C. difficile BI/NAP1/027, in North America and Europe, with a mortality rate of >10% in people aged over 60. 

Following this outbreak, there were reports of initial cases of this strain in Australia, South Korea, Hong Kong and Costa Rica. Considering the high mortality, the emergence of this highly virulent strain is a worldwide concern (4).

This review aims to increase awareness of the importance of C. difficile infection as a nosocomial infection, and to update knowledge on current epidemiology in Australia.

Microbiology

C. difficile is an obligate anaerobe (5), Gram-positive bacillus that can exist in a vegetative or spore form. In its spore form, the bacteria can survive harsh environments and common disinfection techniques.  The spores are also resistant to antibiotics, thus they can remain in the gastrointestinal tract and potentially contribute to recurrent disease after treatment and eradication of vegetative C. difficile (6).

C. difficile colonises 60-70% of healthy newborns and infants aged 12-18 months (6), however in adults, it is only present in the stools of 5% of healthy individuals (7).

Virulence Factors

The primary virulence factors are the two toxins, toxin A (TcdA) and toxin B (TcdB).
TcdA causes fluid secretion, mucosal damage, and intestinal inflammation, while TcdB is a cytotoxin (2).

The epidemic C. difficile strain (BI/NAP1/027) has an 18 base pair deletion within the TdcC gene (negative regulator for the production of TcdA and TcdB), as well as a deletion at position 117. These deletions result in a truncated TcdC protein. Due to the defective negative regulator, they are able to produce significantly more toxin, which has been associated with increased disease severity (8).

This strain has also been shown to produce a third toxin, C. difficile toxin (CDT), which is a binary toxin. CDT induces microtubule protrusions at the cell surface of intestinal epithelial cells, therefore increasing adherence (8). This hypervirulent strain also shows resistance to newer fluoroquinolone antibiotics, such as moxifloxacin (9).

Pathogenesis

C. difficile is transmitted by the faecal-oral route (2). There is a preference for the large bowel for colonisation, which is probably due to the anaerobic environment; while colonisation in the small bowel is quite rare (6). Once the spores have reached an appropriate location within the gastrointestinal tract, germination occurs. After germination, C. difficile adheres to the intestinal epithelium. In the hypervirulent BI/NAP1/027 strain, adherence is increased by CDT. After or during colonisation, vegetative C. difficile releases TcdA and/or TcdB into the colon, which leads to clinical manifestations of C. difficile infection. However, the non-toxin producing C. difficile strain will not result in clinical disease (6,10).

Risk Factors

The risk for acquiring C. difficile infection is increased by factors that impair the normal resistance mechanisms, including disruption of host flora by antibiotics, gastric acid suppression, immunosuppression, or cytotoxic drugs that may result in C. difficile colonisation in the gastrointestinal tract (9).

Many antibiotics have been implicated in C. difficile infection, but the most common ones are broad spectrum agents, such as ampicillin, amoxycillin, third and fourth generation cephalosporins, and clindamycin (9).

C. difficile infection should be suspected in any hospitalised patient or any person in the community who develops diarrhoea after a course of antibiotics or in association with immunosuppressive therapy.

Clinical Presentation

The severity of C. difficile infection varies from mild diarrhoea to pseudomembranous colitis, toxic megacolon and death (10). The symptoms usually occur five to ten days after commencing antibiotic therapy (9).

Diarrhoea is usually watery, but may occasionally be bloody. Other associated symptoms include fever, anorexia, nausea, and abdominal pain. An elevated white cell count and hypoalbuminaemia also commonly occur (9).

Clinical features of severe C. difficile infection include fever (>38.5°C), peritonitis, evidence of bowel perforation, the presence of ileus, and/or toxic megacolon. Laboratory findings associated with severe C. difficile infection include lactic acidosis, elevated white cell count, low albumin level, and acute renal impairment. The presence of pseudomembranous colitis on colonoscopy and radiological evidence of dilatation of the large bowel without involvement of the small bowel, thickening of the bowel wall, perforation, or unexplained ascites, are also strongly suggestive of severe C. difficile infection (9).

Risk factors associated with poor prognosis include age over 60 years, significant underlying comorbid conditions or organ dysfunction, and immunocompromised status (9).

Diagnosis

In Australia, laboratory diagnosis of C. difficile infection is most commonly made through detection of C. difficile TcdA and TcdB using Enzyme Immunoassay (EIA) kits. Despite limitation of its sensitivity (75-95%), it remains widely used due to its simplicity and relatively low cost (11).
Commercial real-time Polymerase Chain Reaction (PCR) testing for toxin genes, has better sensitivity (93%) and specificity (97%), and is now available in many Australian laboratories (11). Other methods of diagnosis include anaerobic toxigenic culture, screening EIA to detect C. difficile glutamate dehydrogenase (GDH), and cell culture cytotoxicity neutralisation assay (CCNAs) (12).
Anaerobic toxigenic culture is extremely sensitive, but is labour intensive and takes at least three days (4).  Screening EIA to detect GDH has high sensitivity but is not very specific, while CCNAs takes 24 to 72 hours to complete (12).

Some commercially available PCR methods can presumptively identify PCR ribotype 027 based on detection of binary toxin genes and the 18-base-pair deletion in the TdcC (4). An alternative is to screen for moxifloxacin resistance, as most BI/NAP1/027 isolates are resistant to moxifloxacin (9).

Repeat testing is not indicated within 30 days of initial detection, as 25-30% of patients have asymptomatic carriage within this period (9).

Treatment

The current treatment for C. difficile infection based on Australian Society for Infectious Diseases (ASID) guidelines is metronidazole for mild to moderate disease, and oral vancomycin for severe disease. The oral route is preferred for metronidazole administration as the concentration in the colon is similar after oral and intravenous administration in patients with ileus. A ten day course is usually used, but a longer course may be indicated, although it should not be used for longer than four to six weeks due to the potential for peripheral neuropathy.

Vancomycin is more effective in severe C. difficile infection and is associated with lower rates of treatment failure and relapse than metronidazole. Vancomycin achieves a much higher concentration following oral administration than intravenously, as it is not absorbed in the gut. Vancomycin can also be administered as a retention enema, particularly in cases of ileus.
Surgery is indicated if there are signs of bowel perforation, toxic megacolon, and/or ongoing severe sepsis despite antibiotic treatment. The most commonly performed surgery is subtotal colectomy, with an end-ileostomy.

Recurrent C. difficile infection should be treated with re-administration of metronidazole or vancomycin, as for an initial episode. However, for second or subsequent recurrences, an alternative antibiotic is preferable, due to concerns about the cumulative toxicity of metronidazole. Alternative therapies for this include bacitracin, tigecycline, fusidic acid, and faecal enemas (“stool transplant”).

Prevention

The hospital environment, as well as chronic care facilities, can become grossly contaminated with C. difficile spores, which can persist for months to years and be easily transmitted by hands of healthcare workers, unless methods of cleaning and disinfection that remove or kill spores are used (2, 9) in addition to hand hygiene before and after contact with patients and their immediate environment. Alcohol-based hand rub is effective against the vegetative form, but not as effective against spores as hand washing, which physically removes spores (9).

Epidemiology in Australia

Limited data were available from Australia on the incidence of C. difficile infection and the distribution of the various ribotypes before the introduction of ribotype 027 (8). The first case of C. difficile ribotype 027 thought to have been acquired in Australia was in an 83 year-old man who developed watery diarrhoea and subsequently toxic megacolon post-aortic valve replacement (13). Since then, there have been further clusters of C. difficile ribotype 027 infections centred in residential aged-care facilities.

C. difficile Infection Surveillance in Australia

C. difficile is not notifiable to public health authorities in any jurisdiction in Australia, and there are no known formal patient-based surveillance systems for notification of severe C. difficile infection cases or outbreaks, nor a reference laboratory for C. difficile typing. Draft definitions for laboratory–based C. difficile infection surveillance were proposed in 2002; however they have not yet been widely adopted (14). Nevertheless, C. difficile infection is one of the markers of healthcare-associated infections, recommended by the Australian Commission on Safety and Quality in Healthcare, and national surveillance will be introduced soon (15).

Conclusion

C. difficile infection is the commonest cause of nosocomial infection and antibiotic-associated diarrhoea, with high morbidity and mortality, causing extra costs and pressures on the healthcare system.  The emergence and outbreak of highly virulent C. difficile BI/NAP1/027 in North America and Europe, followed by its detection in Australia, highlight the need for increased awareness and a better surveillance of C. difficile infection in Australia.

Acknowledgement
Prof. Lyn Gilbert (Director of Centre for Infectious Diseases and Microbiology – Public Health, Westmead Hospital)

 Conflicts of Interest
None declared.

References

  1. Australasian Society for Infectious Diseases. Australasian Society for Infectious Diseases guidelines for the diagnosis and treatment of Clostridium difficile infection. Australasian Society for Infectious Diseases. 2010.
  2. Kelly CP, Pothoulakis C, LaMont JT.  Clostridium difficile colitis. N Engl J Med. 1994; 330(4):257-62.
  3. 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(3):346-53.
  4. Richards M, Knox J, Elliott B, Mackin K, Lyras D, Waring LJ, et al. Severe infection with Clostridium difficile PCR ribotype 027 acquired in Melbourne, Australia. Med J Aust. 2011;194(7):369-71.
  5. Gerding DN, Johnson S. Chapter 129. Clostridium Difficile Infection, Including Pseudomembranous Colitis. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, editors. Harrison's Principles of Internal Medicine. 18th ed. New York: McGraw-Hill; 2012.
  6. Heinlen L, Ballard JD. Clostridium difficile Infection. Am J Med Sci. 2010;340(3):247-52.
  7. Kachrimanidou M, Malisiovas N. Clostridium difficile Infection: A Comprehensive Review. Cr Rev Microbiol. 2011; 37(3):178-87.
  8. Freeman J, Bauer MP, Baines SD, Corver J, Fawley WN, Goorhuis B, et al. The Changing Epidemiology of Clostridium difficile Infections. Clin Microbiol Rev. 2010;23(3):529.
  9. Cheng AC, Ferguson JK, Richards MJ, Robson JM, Gilbert GL, McGregor A, et al. Australasian Society for Infectious Diseases guidelines for the diagnosis and treatment of Clostridium difficile infection. Med J Aust. 2011;194(7):353-8.
  10. Elliott B, Chang BJ, Golledge CL, Riley TV. Clostridium difficile-associated diarrhoea. Intern Med J. 2007;37(8):561-8.
  11. Ferguson JK, Cheng AC, Gilbert GL, Gottlieb T, Korman T, McGregor A, et al. Clostridium difficile laboratory testing in Australia and New Zealand: national survey results and Australian Society for Infectious Diseases recommendations for best practice. Pathology 2011; 43(5):482-7.
  12. Carroll KC. Tests for the diagnosis of Clostridium difficile: the next generation. Anaerobe 2011; 17(4):170-4.
  13. Stuart RL, Marshall C. Clostridium difficile infection: a new threat on our doorstep. Med J Aust.  2011;194(7):331-2.
  14. McGregor A, Riley TV, Gessel HV. Clostridium difficile associated disease. In:  Cruikshank M, Ferguson J, editors. Reducing harm to patients from healthcare associated infection: the role of surveillance. Australian Commission on Safety and Quality of Healthcare; 2008. p. 171-87.
  15. Bull AL, Worth LJ, Richards MJ. Implementation of standardised surveillance for Clostridium difficile infections in Australia: initial report from the Victorian Healthcare Associated Infection Surveillance System. Intern Med J. 2012;42(6):715-8.