As of 2005, outbreaks with “hypervirulent” Clostridium difficile PCR ribotype 027 were recognized in the Netherlands. Soon after their recognition, the Center for Infectious Disease Control (CIb) of the National Institute for Public Health and the Environment (RIVM) started a typing service for C. difficile at the Leiden University Medical Center (LUMC). This “ad hoc typing” service was offered to all microbiological laboratories in the Netherlands, and medical microbiologists were requested to send C. difficile samples from patients with severe C. difficile infection (CDI) and from outbreaks to the Reference Laboratory.