INTRODUCTION

Nosocomial pneumonia (NP) may be defined as a pneumonia that occurs in the hospital. Nosocomial pneumonia is synonymous with hospital-acquired pneumonia (HAP). There is a subset of NP and HAP of patients who are on ventilators, and this subset of patients are referred to as ventilator-associated pneumonias (VAP). NP/HAP may be considered as early NP/HAP, ie, occurring ≤5 days after hospital admission, or as late NP/HAP occurring ≤5 days after hospital admission. There is little clinical rationale for this distinction except that it can skew the data in studies and affect mortality outcomes and initial empiric therapy that differ between the “early” and “late” NP/HAP. “Early” NP/HAP really represents incubating community-acquired pneumonia (CAP) that has become clinically manifest within 5 days of admission to the hospital. Therefore, the organisms in the early NP/HAP group are really CAP pathogens, predominantly Streptococcus pneumoniae. In the traditional group of NP/HAP, ie, the late-onset NP/HAP, the organisms are reflective of the aerobic gram-negative bacillary flora of the hospital. Because early NP/HAP is really CAP manifesting in the hospital, henceforth it will be termed late onset NP/HAP. The most important, albeit not the most frequent, pathogen in the NP/HAP group is Pseudomonas aeruginosa. Other gram-negative bacilli are also major pathogens in NP/HAP, eg, Klebsiella pneumoniae and Serratia marcescens.