An early Legionnaires' disease epidemic affected residents of a large psychiatric hospital (St. Elizabeth's) in Washington, DC, USA. The hospital housed about 6000 patients in multiple buildings on a 350 acre (1.4 km2) campus.

In July to August 1965, at least 81 hospital patients developed pneumonia, 14 (17%) of whom died. Cephalosporin therapy was ineffective, but tetracycline plus streptomycin treatment appeared to have to some beneficial effect. Sleeping near open windows and having permission to walk on the hospital grounds were found to be the most significant risk factors for acquiring pneumonia. Soil excavation work for a lawn sprinkling system was causing very dusty conditions. A strong wind storm and summer rains occurred concurrent with the outbreak, which ended spontaneously, and contemporaneously with the cessation of the excavation work. A soil or dust borne pathogen was thought to be most likely. Extensive microbiological testing of lungs from dead patients and of the hospital environment, failed to reveal an aetiology for the epidemic.

However, analysis of stored serum specimens in 1977 showed that 19 of 26 patients tested seroconverted to Legionella pneumophila serogroup 1. Subsequent Legionnaires' disease epidemics have rarely implicated soil excavation, although disruptions of potable water systems and contamination of building plumbing systems during construction have been alternative explanations.

An interesting historical note is that the attempted assassin of US President Ronald Reagan is currently confined to this institution.

from Legionnaires Disease: History and Clinical Findings

Further reading: Legionella: Molecular Microbiology

Labels: legionella, legionellosis, Legionnaires disease