The changing microbiologic epidemiology of community-acquired pneumonia.

Community-acquired pneumonia (CAP) is a common infectious disease in the United States and the incidence continues to grow as the aging population increases. Overall, in-hospital patient mortality rates have been reported to be as high as 18%. Management of patients with CAP has been challenged by the evolution of resistant pathogens (particularly Streptococcus pneumoniae and Staphylococcus aureus) that have reduced susceptibility to recommended standard antimicrobial agents. Streptococcus pneumoniae continues to be the most frequently identified pathogen in CAP and recently, S. aureus has been found to be the second most often identified pathogen. Data from the SENTRY Antimicrobial Surveillance Program has shown declining susceptibility of pneumococci to penicillin, amoxicillin/clavulanate, and ceftriaxone from 1998 through 2011. In the Assessing Worldwide Resistance Evaluation (AWARE) surveillance program, > 50% of all S. aureus isolates from patient bloodstream infections, skin and skin structure infections, and pneumonia were methicillin-resistant. Stratifying risk factors to identify patients at risk for community-acquired multidrug-resistant pathogens should be considered when selecting therapy. Differences in microbiology and outcomes have been noted in patients presenting from the community with recent exposure to the health care system (eg, nursing home residents, patients with a recent hospital admission). These patients are at an increased risk of an infection caused by a multidrug-resistant pathogen. Understanding a patient's risk for drug-resistant pathogens will allow the physician to choose an appropriate empiric treatment regimen to optimize clinical outcomes.