Simultaneous outbreaks of two strains of toxigenic Clostridium difficile in a general hospital

We report an outbreak of Clostridium difficile-associated disease (CDAD) in a large Dublin hospital. From January to June 1995, inclusive, 139 patients were affected; the mean age of cases was 68.8+/-19 years. Clinical information is available for 73 cases identified during the first four months of the outbreak. The majority of patients presented with abrupt onset of watery diarrhoea; however, 19.2% presented with an unexplained pyrexia following a course of antimicrobial therapy and 5.5% presented with a surgical acute abdomen. Twenty patients (27.4%) experienced relapsing disease and seven (9.6%) patients died. Seventy-six percent of cases received a cephalosporin prior to the onset of disease, the highest relative risks occurring with third-generation agents; however, 9.6% of patients affected had not been exposed to antimicrobial therapy in the preceding eight weeks. Pyrolysis mass spectrometry identified two clusters of isolates, representing two strains of C. difficile. There was marked spatial clustering of these strains, with each confined to a separate area of the hospital. Infection control measures and an antibiotic policy were introduced. Throughout the outbreak period the use of the most frequently used cephalosporin in the hospital increased; this was accompanied paradoxically by a reduction in the number of new cases of CDAD.