Abstract
During late December 1989 and early January 1990, a cluster of six unexplained deaths occurred on a paediatric intensive care unit (PICU) among children with congenital heart disease who had undergone cardiac surgical procedures. The children were all aged three years or less. In each case death was preceded by an unexpected increase in ventilatory pressure requirement followed by the development of a similar pulmonary shadowing on chest radiography. The radiological abnormality was felt to be consistent with a pneumonitis associated with some small airway disease. The clustering of these deaths, occurring in a similar unusual manner, was felt to constitute an outbreak warranting investigation. An Incident Committee was established to plan and manage a large multidisciplinary investigation during which the unit was temporarily closed. Following extensive investigation no bacterium, virus, fungus or other pathogen, toxic agent, or any other explanation for the cluster of deaths could be found. The possibility that the cluster occurred by chance remains although this was felt to be unlikely.