Pneumonia caused by gram-negative bacilli.

Gram-negative bacillary pneumonia has become an increasingly important disease in immunosuppressed, elderly, and hospitalized patients. The clinical features, etiologic agents, population at risk, treatment, and outcome in patients with well-documented gram-negative pneumonia were compared in two groups of patients: those with bacteremic pneumonia and those with nonbacteremic pneumonia documented by transtracheal aspiration. Clinical features were frequently subtle in both groups. A wide range of gram-negative bacilli were implicated as pathogens and pneumonias documented by transtracheal aspiration were frequently mixed infections. Pseudomonas aeruginosa and Serratia marcescens were the most common pathogens causing bacteremic pneumonias, whereas Escherichia coli and Klebsiella were more common in the nonbacteremic group. Gram-negative bacillary pneumonia was frequently a lethal disease despite two-drug therapy, particularly in bacteremic patients.