Healthcare-Associated Pneumonia: Epidemiology, Microbiology and Clinical Outcomes

Pneumonia is one of the leading causes of hospitalisation and mortality in the United States [1]. Effective empiric treatment involves selecting an antibiotic with a spectrum of activity that includes the possible causative pathogen(s) [1]. Therefore, an evidence-based classification scheme that differentiates pneumonia based on the most likely causative organism(s) will help clinicians maximize the likelihood of providing the correct treatment and achieve favourable outcomes. Community-acquired pneumonia (CAP) is defined as signs, symptoms and radiographic evidence of pneumonia present in patients that come from the community which develop within 48 hours of hospital admission. In contrast, hospital-acquired pneumonia (HAP) is diagnosed as the presence of respiratory signs, symptoms and radiological evidence of pneumonia that begin after 48−72 hours of hospital admission. This classification is based in part due to differences in underlying etiologic pathogens, but despite the wide use of this dichotomous classification for pneumonia, data related to a variety of infectious processes indicate that these classifications may have significant limitations.