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Whether in the emergency department or in the intensive care unit (ICU), pneumonia is a disease with which all treating clinicians must be familiar. In order to accurately recognize and appropriately manage pneumonia, one must first understand its varying classifications, affiliated pathogens, available diagnostic methods, treatment options, and methods of prevention.

Pneumonia classically has been dichotomized as either community-acquired pneumonia (CAP) or nosocomial pneumonia (NP), depending on where the patient becomes infected. NP must occur at least 48 hours after hospital admission and not be incubating at the time of admission.1 NP developing in an individual after requiring at least 48 hours of mechanical ventilation is termed ventilator-associated pneumonia (VAP). NP can also be categorized according to the timing of its onset following hospital admission. Early onset NP occurs within the first 4 days of hospitalization and can be due to antibiotic-susceptible bacteria found in the community (e.g., Pneumococcus, H. influenzae, Moraxella).2 Late-onset NP occurs after at least 5 hospital days, is generally caused by multidrug-resistant (MDR) organisms (e.g., P. aeruginosa, Acinetobacter spp.), and has a higher associated mortality.3 These definitions are clinically relevant because each is associated with a distinct set of typical infecting organisms, management strategies, and outcomes.

However, as the lines between typical outpatient and inpatient settings blur (e.g., due to increased utilization of outpatient dialysis, surgical, and rehabilitation centers), these standard definitions inadequately account for the evolving landscape of causative bacteria resulting in pneumonia. The type of pneumonia infecting individuals with exposure to health care settings is now termed health care–associated pneumonia (HCAP). Although this type of pneumonia typically presents in individuals technically living in the community, the bacterial flora and clinical outcomes affiliated with HCAP are generally similar to those of NP. Therefore, assessing a patient's risk factors for HCAP is essential for its prompt identification and subsequent antibiotic selection (Table 37-1).

Table 37-1. Nosocomial Pneumonia (NP) and Health Care–Associated Pneumonia (HCAP) Risk Factors for Multidrug Resistance

Pneumonia exacts a great toll on the physical and financial health of both individuals and society. Compared with the estimated 10% mortality with CAP, one review of over 4,500 hospitalized patients demonstrated mortalities of 19.8% with HCAP and 18.8% with NP.4 NP, and in particular VAP, has an expectedly high mortality due to the ...

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