An outbreak of Legionnaires' pneumonia in a nursing home.

An outbreak of Legionnaires' pneumonia occurred at a nursing home in December 1990. A 79-year-old female and a 73-year-old male clerk who were staying at the nursing home developed pneumonia with only a 5-day interval. Legionella pneumophila serogroup I was isolated from transtracheal aspirate of the former and sputum of the latter. After treatment with a combination of erythromycin and rifampicin both patients improved. Serological surveillance of inpatients and staff of the nursing home was performed in February 1991. Seven out of 51 samples (14.0%) showed a titer higher than 1:128 of anti-Legionella pneumophila serogroup I antibody determined by indirect immunofluorescence; two of these seven complained of respiratory symptoms. Molecular epidemiology analyzed by restriction endonuclease digestion of isolated L. pneumophila showed an identical pattern which suggested a common origin.