Legionnaires' disease in a Johannesburg teaching hospital. Investigation and control of an outbreak.

During the period 11 November 1985 - 21 February 1986, 12 cases of Legionnaires' disease were identified at a Johannesburg teaching hospital. Only 2 patients definitely acquired the disease in hospital. Both responded well to treatment. An epidemiological investigation was initiated to determine the source of infection and mode of transmission of the causative agent (Legionella pneumophila), which may be recovered from a wide variety of water sources. Although L. pneumophila was cultured from the hospital hot-water system, there was no association between the location of patients and culture-positive water sites. Cases were clustered in the medical and surgical intensive care units. Being on a ventilator was a significant risk factor for acquiring Legionnaires' disease (relative risk 18,4; 95% confidence interval 2,4 - 142,2). The potential role of ventilators in the transmission of the disease is discussed together with the infection control measures adopted to interrupt the outbreak. To our knowledge this is the first investigation of an outbreak of Legionnaires' disease in South Africa.