CASE STUDY 1

The following case outlines an investigative process and illustrates that the source of an outbreak may be unusual [336].

A cardiac surgeon noticed a cluster of cases of sternal wound dehiscence among his patients who had had surgery. Specimens from the wounds were obtained for culture. Microbiologic evaluation indicated that the infections were predominantly caused by Enterobacter cloacae, and molecular typing and serotyping demonstrated that the isolates were similar. No infections had developed after operations the surgeon had performed at other hospitals. No breach in aseptic technique was identified. All of the infected patients had been operated on in the same operating room, and the environment was screened. No source was found. Further questioning of the surgeon's operative practice revealed one difference from other cardiac surgeons: he used semi-frozen sodium lactate solution to achieve cardioplegia. Swabbing of the freezer used for the solution identified E. cloacae of the same typing as that found in the wound infections. The hypothesis was that contamination of the freezer led to contamination of the ice/slush solution, and the micro-organism was transmitted to the patients. The freezer was replaced, a rigorous cleaning schedule was instituted, and no further cases have occurred.