Cl. difficile can be transmitted from patient-to-patient, via contaminated hands of healthcare workers or by contaminated environmental surfaces. The bacterium can be found in the stools of 3% of healthy adults and up to 80% of healthy newborns and infants (2). Stool carriage of Cl. difficile reaches 16-35% in hospital patients and the percentage is proportional to the duration of hospital stay and increases with exposure to antibiotics. Cl. difficile is well known to persist in the stools of 10-40% of patients with Clostridium difficile-associated diarrhea (CDAD) irrespective of the antibiotic treatment (3). The role of symptom free healthcare workers and patients with Cl. difficile in the intestinal tract in spreading of the bacterium is unclear. Contamination with Cl. difficile spores has been demonstrated in 30-60% of sites in hospital wards (4).
In humans Cl. difficile can clinically cause pseudomembraneous colitis and Clostridium difficile-associated diarrhea. The clinical spectrum of CDAD ranges from asymptomatic carriage to a fulminant, relapsing and potentially fatal colitis with mortality from 6% to 30% (2). The elderly and immuno-compromised persons are particularly at risk. Eighty percent of CDAD cases occur in persons over 65 year of age.
CDAD has been considered to be an antibiotic-associated nosocomial infection. However, community-aquired CDAD is increasing.I In Philadelphia (US) 30% of patients with CDAD had no previous use of antibiotics; the minimum annual incidence of community-aquired CDAD was estimated to be 7.6 cases per 100,000 population or 1 case per 5,000 outpatient antimicrobial prescriptions (5). In UK the incidence of Cl. difficile had increased from less than 1 case per 100,000 in 1994 to 22 per 100,000 in 2004 (6).
The origins of CDAD are defined as follows (7) (Table 1):
Characteristics of Clostridium difficile variant 027
Enteropathogenic Cl. difficile release two potent toxins that mediate diarrhea and colitis: toxin A, a 308-kd enterotoxin, and toxin B, a 269-kd cytotoxin. The toxins are produced simultaneously and working synergistically. A recently discovered binary toxin that is present in approximately 6% of Cl. difficile strains is a new virulence marker (8). Binary toxin genes were found in nearly two-thirds of the Cl. difficile strains (9).
Cl. difficile may be divided into more than 150 ribotypes and 24 toxinotypes. Diagnostic assays include tests for the detection of Cl. difficile products (toxins, glutamate dehydrogenase, volatile fatty acids), tests for the detection of Cl. difficile genes (16S RNA, toxin genes) and culture methods for the isolation of toxin-producing bacteria (10).
Epidemiological advances have relied on real-time PCR, a method that yields results within a working day, and a recently developed membrane immunochromatography assay that provides results within 15-30 minutes (11). Currently, PCR ribotyping is considered to be the gold standard for Cl. Difficile typing. In Canada, USA, UK, The Netherlands and Belgium an epidemic strain of Cl. difficile was isolated. This strain was characterized as toxinotype III, North American PFGE type 1, restriction-endonuclease analysis group B1 and PCR-ribotype 027. Toxinotype III isolates produce toxins A and B in considerably greater quantities than toxinotype 0 isolates (12). PCR-ribotype 027 was first isolated in 1988 from a 28-year old woman with severe pseudomembraneous colitis and was until 2004 considered to be an unimportant and rare PCR-ribotype (9).
Evidence of increased virulence of Clostridium difficile variant 027
The rate and severity associated with a more virulent strain of Cl. difficile NAP1/027 is increasing in Europe and North America. In 2004 at twelve hospitals in Quebec, Canada, the CDAD incidence was 22.5 cases per 1,000 hospital admissions with a case fatality of 6.9%. Both incidence and fatality increased with increasing age. Most patients were treated with fluoroquinolones and cephalosporins (13). Resistance to fluoroquinolones was indentified in 82.2% of patients and 84.1% of isolates had binary toxin genes (14). In the USA, CDAD hospital discharges doubled between 1996 and 2003. At least half of the isolates belonged to group B1, PFGE type NAP1 and were positive for the binary toxin. Resistance to moxifloxacin and gatifloxacin was common among B1/NAP1 strains of Cl. difficile.
Outbreaks of CDAD due to highly virulent strain of Cl. difficile PCR-ribotype 027 were recognized in 44 hospitals in England, 8 hospitals in The Netherlands and 6 hospitals in Belgium. During the period from February until June 2004 ribotype 027 strain was detected at a hospital outbreak in the UK involving 150 patients that resulted in twelve deaths (15). In a hospital in Harderwijk (The Netherlands) the CDAD incidence increased from 4 per 10,000 patient admissions in 2004 to 83 per 10 000 during April through July 2005. Isolates were identified as toxinotype III and ribotype 027. A second outbreak that was related to the first outbreak occurred when a patient with CDAD was transferred to the neighborhood hospital;. 85 CDAD patients were identified by December 2005, 22% of the patients died and 19% relapses were observed (16). In September 2005, the ribotype 027 incidence increased in CDAD patients from 10 per 10,000 admissions to 33 per 10,000. The same pattern was identified among strains from three outbreaks that occurred in Brussels, Belgium in 2003-2004 (17).
Although CDAD presents most frequently as a hospital acquired infection, recent reports indicate an increase of community-acquired CDAD in populations not considered to be at risk.
There exists a severe underestimation of CDAD in Europe due to a lack of awareness among physicians and lack of standardized diagnostic strategies (18). The association between CDAD and antibiotic use is overestimated because the disease also occurs in patients without previous antibiotic treatment.
Depending on the nature of the notifications, a public health system can implement laboratory-based or case-based surveillance measures in specific, targeted populations (e.g. patients in hospitals, patients in nursing homes/long-term care facilities, in patients under the care of GPs). Mandatory reporting of CDAD cases was first introduced in UK in 2004. The surveillance has been restricted to patients over 65 years old, regardless of the presence or absence of any specific risk factors (e.g. prior antimicrobial therapy) and to hospital-acquired CDAD.
A CDAD case definition is essential for surveillance. The following case definition, proposed by B. Coignard and F. Barbut, is based on experience from Canada, USA, UK and The Netherlands. (Table 2).
An outbreak of CDAD is defined as the occurrence of two or more related cases of CDAD over a defined period, taking into account the background rate.
Prevention of CDAD outbreaks can only be accomplished by early recognition, adequate isolation measures and prompt treatment. Based on the recent experiences with epidemics of Cl. difficile variant 027, microbiological laboratories should implement a new rapid immunoassay test as well as RT-PCR in routine CDAD diagnostics. The medical microbiological laboratories should have a central role in the surveillance of CDAD.
The impact of CDAD
The impact of CDAD on healthcare systems is significant. Available data indicate that nosocomial CDAD cases spend from one to three extra weeks in hospital. In the USA, the number of hospital discharge diagnoses of CDAD in 2001-2003 exceeded the estimated annual number of methicillin-resistant S. aureus infections. In addition, Cl. difficile mortality was twice as high as that due to MRSA among patients in 2003(19). In terms of costs the impact of CDAD translates into 5,000-15,000 euros per case in UK and 1.1 billion dollars in the United States. Assuming a population of 457 million persons in the European Union, CDAD may potentially cost the community 3 billion euros per annum. The cost is expected to double over the next four decades.
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