Etiology of pneumonia requiring ICU admission - intensive care unit - Tips from Other Journals

Date: June, 1992

Effective treatment of pneumonia relies on the accurate prediction of the responsible organism. Although the pathogens in pneumonia are well known, the characteristics of pneumonia necessitating admission to the intensive care unit have not been well defined. To investigate the spectrum of infecting agents and the efficacy of routine microbiologic investigations used to make the diagnosis, Potgieter and Hammond studied patients with pneumonia admitted to the intensive care unit.

The study included 178 patients admitted to the intensive care unit with a clinical diagnosis of pneumonia. The decision to admit to the intensive care unit was made on clinical grounds. Based on the type of pneumonia, patients were divided into four groups: (1) patients with primary pneumonia that occurred in the community; (2) patients with nosocomial pneumonia or pneumonia that developed 48 hours after hospital admission; (3) immunocompromised patients with pneumonia, including patients receiving systemic steroids and those with malignancies, and (4) patients with aspiration pneumonia.

Pathogens were identified from sputum culture, Gram stain, blood culture and serology. The cause of the pneumonia was identified in 68 percent of patients who had sputum and/or tracheal aspirate culture, 54 percent of those who had blood culture and 15 percent of those who had serologic testing. Seven patients had an etiologic diagnosis as a result of bronchoscopy, and two patients who underwent open lung biopsy had a confirmed diagnosis.

The most common etiologic agents identified in primary pneumonia, in descending order of frequency, were Streptococcus pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, Staphylococcus aureus, Legionella pneumophila and Escherichia coli. The most common pathogens in nosocomial pneumonia were S. aureus, S. pneumoniae and H. influenzae. Aspiration pneumonia resulted from infection with S. pneumoniae, H. influenzae, S. aureus, K. pneumoniae and E. coli. In immunocompromised patients, S. pneumoniae was again the predominant organism, followed by S. aureus, H. influenzae, K. pneumoniae and viral pathogens.

The authors conclude that in this study, the incidence of Mycoplasma pneumoniae infection was low, while the incidence of gram-negative infections in primary pneumonia was much higher than that in community- or general hospital-based studies. Gram stain of sputum or tracheal aspirate in primary pneumonia reliably predicted the causative organisms, when the compared with infections proved by blood culture. Bronchoscopy contributed minimally to diagnosis, while serologic studies were valuable in patients in whom no positive microbiologic diagnosis was evident. (Chest, January 1992, vol. 101, p. 199).

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