What are the important risk factors for healthcare-associated pneumonia?

Healthcare-associated pneumonia (HCAP) is a category of nosocomial pneumonia defined by the 2005 American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) guidelines to include any patient who has been hospitalized in an acute care hospital for 2 or more days within the past 90 days; residents of a nursing home or long-term care facility; recipients of recent intravenous antibiotic therapy, chemotherapy, or wound care within the past 30 days; or patients who have attended a hospital or hemodialysis clinic. In creating this relatively new category the ATS/IDSA acknowledged that these patients are at increased risk for infection with antibiotic-resistant organisms and that initial inadequate antibiotic coverage leads to increased mortality. Risk factors for the development of pneumonia and the development of pneumonia caused by drug-resistant pathogens, primarily methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, are not the same among the subgroups of HCAP (i.e., dialysis patients have different risks than nursing home patients). Furthermore there is significant heterogeneity of risk factors for HCAP within the subgroups due to variations in contextual factors such as local microbiology and methods of health care delivery and variations of individual risk factors such as functional status or prior antibiotic exposure. This review examines the evidence for the creation of the category of HCAP, including the risk factors for drug- resistant pneumonia in each of the subgroups that constitute HCAP. This review demonstrates that the guidelines have effectively targeted a population at greater risk for pneumonia caused by drug-resistant pathogens. However, within the broad range of HCAP infections, there is significant heterogeneity in terms of the magnitude of the risk as well as the type of risk (i.e., risk for MRSA, multidrug-resistant gram-negative bacilli (MDR-GNB), or both).