Prospective study of pneumonia: unexpected incidence of legionellosis.

In a prospective study of the etiology of pneumonia in patients hospitalized at a university hospital, all respiratory secretions were tested for routine pathogens as well as Legionella. A diagnosis was established in 60 of 87 patients studied. Of the 37 nosocomial infections, six were caused by L micdadei. Gram-negative rods, Staphylococcus aureus, and Streptococcus pneumoniae and Haemophilus influenzae were also important organisms in this group. In the community-acquired cases, gram-negative rods caused 26% of infections. These data emphasize both the importance of Legionella in hospitals and the changing spectrum of both hospital- and community-acquired pneumonia.