Fatal Legionnaires' pneumonia: frequency of legionellosis in autopsied patients with pneumonia from 1969 to 1985.

In 89 of 3027 (2.9 per cent) patients in whom pneumonia was found at autopsy during the period from 1969 to 1985, legionella pneumonia was diagnosed. Legionellae were demonstrated through the direct fluorescent antibody test by screening lung tissue sections. All 89 cases were caused by Legionella pneumophila. Suspicious typical rod-shaped organisms were demonstrated in all cases by the modified Dieterle stain whereas conventional histological stains failed to detect causative bacteria. The frequency per year of legionellosis in patients with pneumonia at autopsy ranged from 1.4 per cent (3/212 cases) to 6.8 per cent (12/177 cases). In patients who have died of unexplained pneumonia, examinations for the demonstration of legionellae should be carried out.