Hypervirulent Strains Of Clostridium Difficile
By Dr. Barry Cookson, Centre for Infections, Health Protection Agency, UK

The anaerobic, gram-positive, spore-forming bacterium Clostridium difficile was first isolated in 1935. The designated name related to how difficult the original investigators found it to culture. It has been isolated widely in the soil and the gut of many animals and, although a known cause of colitis in animals such as cats, dogs, birds, rodents and neonatal pigs, it was not until 1978 that it was found to also cause human disease (pseudomembranous colitis).

CAUSES  OF CDAD
Risk factors for (itals)Clostridium difficile associated diarrhoea (CDAD) comprise those that affect the gut microbial flora, the most common being exposure to antibiotics. Almost all antibiotics have been associated with CDAD, although it is less often associated with some – for example, metronidazole, aminoglycosides, trimethoprim and the quinolones. Clindamycin historically had a particularly infamous relationship to CDAD; animal work showed that following its use there was a particularly long period of gut susceptibility to the disease when challenged with C. difficile spores. CDAD is a disease predominantly of the aged, but other factors include recent gastrointestinal surgery and immunosuppressive therapy, including cytotoxics. Other independent risk factors described more recently comprise proton pump inhibitors, which increase the risk threefold. It is presumed that increased gastric pH leads to decreased destruction of spores, but colonic receptors do exist for some proton inhibitors.

HYPERVIRULENT CDAD IN NORTH AMERICA
Increased numbers of patients requiring colectomy alerted a hospital in Montreal in 2002 to the possibility of CDAD with a higher severity, mortality and relapse rate. Over the next two years several investigations were performed: rates of CDAD were 28/1000 admissions (five times the national average of 1997) with an extra 10.7 days in hospital and 30-day attributed mortality rates of 6.9 per cent, these being  0.8 to two per cent in 1997. Perforations, toxicmegacolon and colectomy rates had also increased. Between 2004 and 2005 it was estimated that over 14,000 patients had been affected in the province of Quebec, with high mortality and relapse rates. By June 2006 the problem had spread to seven provinces with estimates of 13 cases per 1000 admissions.

Risk factors compared with matched controls comprised, as in many previous studies, cephalosporins (odds ratio [OR] 3.8 per cent, 95 per cent confidence interval [CI] 2.2 per cent to 6.6 per cent) and, for the first time, fluoroquinolones (OR 3.9 per cent, 95 per cent CI 2.3 per cent to 6.6 per cent). Interestingly it may be that the association is only with certain quinolones; methoxyquinolones (gatifloxacin and moxifloxacin) had been introduced recently in several of the affected centres, these agents having greater anaerobic activity. However, the situation with antibiotics was not straightforward, as patients received more antibiotics per case (46 per cent) than controls.

Typing was performed and a new strain (ribotype O27) was isolated from 82 per cent of patients. It was assumed that this was related to the increased virulence and relapse rate. There were other relevant factors, however; hospitals agreed that their case mix had changed over the last few years with greater numbers of debilitated, immunocompromised and elderly patients. Another interesting point is that the study of Pepin and colleagues did not show that proton pump inhibitors were an independent risk factor for CDAD, unlike the study quoted above. There are several possible explanations for this – for example, the patients may have been sicker or have some other missed risk factor. Such a risk factor might include patients admitted from the community.

A similar situation to that in Canada had emerged in the United States, with the Centres for Disease Control and Prevention (CDC) showing rates had doubled between 1996 and 2003 from 31 to 61 cases per 100,000. Isolates from six recent outbreaks in the U.S. revealed emergence of the same epidemic O27 strain. Higher morbidity and mortality were described in at least 17 states. A nursing home outbreak of CDAD could be related to the switching from levafloxacin to gatifloxacin.

PATHOGENESIS OF CDAD
When considering the pathogenesis of CDAD it is important to consider the interactions of the organism (the seed), the affected patients (soil) and the environment (climate). We have already mentioned various aspects of the patient case mix for the Canadian outbreaks and similarly alluded to some of the climatic factors – for example, antibiotic and other drug usage. Although CDAD is under long and continuing study, much is still not know. The inoculum, for example, may be very low.

Several pathogenicity factors are described: there are two large exotoxins (TcdA&B). However, TcdA2/B+ strains are recognized with increasing frequency and truncated A/B strains can cause disease. In 10 per cent of selected strains there is a cdtA-B binary toxin encoding an actin-specific ADP-ribosyltransferase; this may just produce secretion of fluid by colonic cells but does not result in cell death. Many other factors may also be implicated, including fimbriae and sub-groups of adhesions. O27 and O1 may produce higher sporulation levels than other strains and these were even higher when non-chlorinated (i.e. non-oxidating) disinfectants were used.

It should be noted that there has been no consistent relationship between severity of disease and toxin concentration in stool. It is clear that, despite years of research, the organism has many hidden secrets and poses many interesting questions. Interestingly, several of the infection control teams in Quebec comment that they no longer see as many cases of serious CDAD and think this may be related to their aggressive early treatment of infection as soon as the diarrhoea.

PREVENTION AND CONTROL OF CDAD
The number of CDAD cases is increasing throughout the world. This may be related to new factors including the emergence of certain strains, their increasing antimicrobial resistance, the changing case mix, and aspects of healthcare delivery. Prevention and control measures are being reviewed in many countries.

Control will be informed by improved surveillance and typing information. The guidelines point to reinforcement of all of the following: the use of hand washing for soiled hands or close contact with CDAD cases, isolation of patients with diarrhoea, effective stewardship of antibiotics, and proper decontamination of the environment.

A new factor in the rubric of prevention and control are various aspects of clinical governance. These are apparent in reports from the Quebec and other outbreaks. Staffing shortages, high bed occupancy, poorly cleaned and maintained premises, old buildings that need to be replaced, and low priority of infection control resonated. There are other interesting aspects about healthcare delivery. Patient transfers have resulted in the spread of the O27 strain between Belgian and France, and between hospitals in the Netherlands. The O27 strain is now found in many parts of the UK, and it is interesting to speculate whether this may be caused by increased inter-city patient transfers due to patient choice? We described inter-city spread of epidemic methicillin resistant Staphylococcus aureus (MRSA) in the 1990s, perhaps encouraged by this process.

Clearly a holistic approach to prevention and control will be required if we are to make any impact on the increasing numbers of CDAD cases described in many parts of the world.

 - reprinted from Volume 14 of the Virox Technologies’ Solutions newsletter.