Haemophilus influenzae as a Cause of Adult Pneumonia

Abstract
The role of H. influenzae as a pulmonary pathogen in adults is unclear. Part of the problem in ascertaining the significance of this organism can be ascribed to difficulties in obtaining definitive bacteriologic data. Sputa from patients with chronic bronchitis are invariably infected with H. influenzae, and thus the presence of H. influenzae in the sputa of patients with pneumonia does not establish the organism as the etio-logic agent. A 20-month prospective study at a city hospital revealed that adult cases of pneumonia due to H. influenzae are not rare. Six patients had clinical and radiologic evidence of pneumonia and H. influenzae in their blood and sputa. In 5 of the 6 patients the organisms were typed, and in each case the H. influenzae found in the sputa was of the same type as that cultured from the blood. The most frequently observed clinical finding was a history of pulmonary disease. Diabetes mellitus, hematopoietic malignancy, alcoholism and agamma-globulinemia were not prominent features in these patients. Recent experimental data are reviewed which demonstrate that metabolic abnormalities impair pulmonary resistance and allow multiplication of potential pathogens, and suggest that a similar pathogenesis accounts for adult pneumonias due to H. influenzae. It is postulated that in patients with chronic pulmonary infections there is a balance between the infecting H. influenzae and host pulmonary resistance, and that during periods of metabolic disturbance this balance is upset, allowing the development of bacterial pneumonia.

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