Gastric Colonization by Gram-Negative Bacilli and Nosocomial Pneumonia in the Intensive Care Unit Patient Evidence for Causation

The purpose of this article is to assess critically the evidence for a causal relationship between gastric colonization by Gram-negative bacilli and nosocomial pneumonia in the intensive care unit. Articles were found using MEDLINE search and citations in relevant articles. Nine diagnostic tests of causation were applied and analysis showed that the major tests were satisfied. The strongest evidence comes from randomized controlled trials of selective gut decontamination and stress ulcer prophylaxis in intensive care units. These studies confirm that the incidence of nosocomial pneumonia correlates directly with the rate of gastric colonization by Gram-negative bacilli. Further support comes from other tests of causation such as strength and consistency of association, temporal relationship, and dose-response gradient. The data reviewed suggest that gastric colonization with Gram-negative bacilli plays a causal role in the development of nosocomial pneumonia in the intensive care unit patient. This relationship impacts on future studies of pathogenesis and prevention of this potentially lethal infection.