Development of a ‘snapshot' PCR ribotyping scheme within the National Surveillance Program for C. difficile Infection (CDI) in Scotland

Background: A significant increase in the number of laboratory reports of C. difficile in the period 1995-2005 prompted the introduction of a national mandatory surveillance program in all healthcare settings in Scotland in 2006. The program monitors incidence of CDI in patients, aged 65 and over, and the epidemiology of molecular types (PCR ribotypes) of C. difficile in outbreaks and patients with severe disease. Initial setup of the molecular typing scheme focused on cases of severe CDI and outbreaks, and so did not reflect the epidemiology of mild and moderate cases of CDI. There was also potential geographical bias towards regions with many outbreaks and severe cases. We have developed a national ‘snapshot’ PCR ribotyping scheme, which investigates a cross-section of all CDI cases from all healthboard areas, to get a more accurate (and representative) picture of the molecular epidemiology of C. difficile in Scotland.

Objective: This study aimed to develop a national ‘snapshot’ PCR ribotyping scheme that improves the understanding of the epidemiology of C. difficile in Scotland by investigating a cross-section of all CDI cases, including mild, moderate and severe cases from all healthboard areas.

Methods: In the ‘snapshot’ scheme each (National Health Service) diagnostic laboratory in Scotland was assigned a number of isolates to submit to the Scottish C. difficile Reference Service for PCR ribotyping each quarter, based on the median number of cases of CDI per quarter reported from July 2007-June 2008 (laboratories that reported less than 20 cases per quarter should submit 2 isolates). The isolates were typed using PCR ribotyping according to the method of O’Neill et al. and compared to the typing results of severe/outbreak submissions.
Results: A total of 455 isolates (corresponding to ~10% of all diagnosed cases of CDI) were typed in the snapshot scheme and compared to 1618 severe case/outbreak isolates typed in the national program. Ribotypes 106, 001 and 027 (NAP1) were most frequently identified in both groups. A total of 31 less common ribotypes were observed at frequencies < 5% in the snapshot scheme. A higher frequency of ribotype 027 was observed in the snapshot typing scheme than in the severe/outbreak submissions (14.7% vs. 12.1%), while relatively higher frequencies of ribotypes 106 (a ribotype uncommon outside the UK) and 001 were observed in the severe/outbreak submissions (31.0% vs. 24.0% for 106, and 22.8% vs. 19.3% for 001).

Conclusions: The snapshot ribotyping showed that 106, 001 and 027 are the most common ribotypes in a representative cross-section of all diagnosed cases, similar to that previously observed among severe cases and outbreaks of CDI (p=0.34). Nonetheless we note that ribotype 027, often associated with enhanced transmissibility and severity, was found in a higher frequency in the snapshot scheme than among isolates from outbreak and severe cases.