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Nosocomial pneumonia, or terminal pneumonia as it was formerly called, results from the repetitive microaspiration of contaminated oropharyngeal secretions into the lungs in the presence of impaired host defenses. This pathophysiologic sequence was suggested by the observations of Osler but clarified by the seminal work of Rouby and colleagues. The enormous impact of antimicrobial agents on the organisms responsible for nosocomial pneumonias was first identified by Kneeland and Price who found that organisms of the normal pharyngeal flora virtually disappeared in terminal pneumonias following administration of these drugs, being replaced by gram-negative bacilli. The remarkable susceptibility of seriously ill patients to becoming colonized by exogenous organisms, even in the absence of antimicrobial therapy, was shown by Johanson et al. These factors, antibiotics and the change in bacterial binding receptors in the airways associated with illness, lead to infections caused by exogenous organisms that are frequently resistant to antimicrobial agents. Clinical findings that usually identify patients with respiratory infections are unreliable for the diagnosis of nosocomial pneumonias as shown by Andrews et al. Invasive techniques, especially the protected specimen brush (PSB) technique, avoid contamination of the specimen by proximal secretions and accurately reflect the bacterial burden of the lung, as first shown by Chastre et al. Quantitation of such specimens serves as an excellent proxy for direct cultures of the lung and are the current gold standard for diagnosis.

Background: Colonization and infection with vancomycin-resistant Enterococcus faecium (VREF) has been associated with the use of vancomycin and other antibiotics in individual patients. The objective of this study was to determine the association of VREF with the aggregate usage of antibiotics on nursing units in a hospital., Methods: This was a retrospective correlation study. A usage ratio was calculated for each parenteral antibiotic on each nursing unit as the per-bed usage by weight of that antibiotic divided by its average usage throughout the hospital. An average usage ratio (AUR) for each nursing unit was calculated as the mean of usage ratios of individual antibiotics. The AUR was used to compare the usage of antibiotics among nursing units in the hospital. The incidence of VREF infections on individual nursing units in a Veterans Affairs Medical Center was correlated with the usage of parenteral antibiotics separately and in aggregate in univariate and multivariate regression analyses., Results: The AUR was strongly and positively correlated with the recovery of VREF on individual nursing units. By univariate analyses, increasing use of each antibiotic tested was associated with isolation of VREF but only clindamycin remained significant in the multivariate model. However, usage of various antibiotics was highly interrelated, and only clindamycin usage was significantly correlated with usage of all other antibiotics studied. Intensive care and acute care units and units with fewer patient beds were more likely to have patients with VREF infection than were subacute care units (p < 0.003) or larger units (p < 0.01)., Conclusions: VREF infections were associated with greater aggregate antibiotic use on nursing units. Determination of antibiotic usage ratios may provide a convenient and useful tool for examining the association of antibiotic usage with other nosocomial infections.