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Whether in the emergency department (ED) or in the intensive care unit (ICU), pneumonia is a disease with which all treating clinicians must be familiar. Acute pneumonia is the fourth leading cause of death among patients of all age groups worldwide and the leading cause of mortality in low-income countries according to the World Health Organization (WHO).1 The main challenge in the management of this illness is the large number of microbial agents that can cause the disease, in addition to the difficulty of making an etiologic diagnosis before starting treatment. Therefore, antibiotic therapy must be started empirically by clinicians, which may lead to excessive antibiotic coverage, which entails a considerable risk of antibiotic resistance among the common pathogens involved. In order to accurately recognize and appropriately manage pneumonia, healthcare providers must understand the different definitions, microbiology, pathogenesis, and varying treatment guidelines available.


Pneumonia is classified depending on where and when the patient becomes infected. The most updated guidelines from the joint committee between the American Thoracic Society (ATS) and the Infectious Diseases Society of America (IDSA) in 20052 and 2007,3 respectively, focus on evidence-based recommendations for four different categories of pneumonia: community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP), healthcare-associated pneumonia (HCAP), Hospital-Acquired, Health Care-Associated and Ventilator-Associated Pneumonia and ventilator-associated pneumonia (VAP). CAP refers to the lower respiratory infection obtained from normal social contact in the community and will not be discussed in this chapter. Moreover, the category previously known as nosocomial pneumonia now comprises three different clinical settings of infection in patients exposed to different healthcare settings and invasive procedures. HAP is defined as pneumonia that occurs 48 hours or more after admission to the hospital and that was not incubating at the time of that admission. HCAP refers to pneumonia in patients who were acutely hospitalized for two or more days within 90 days of the actual infection; resided in nursing homes or long-term care facilities; received recent intravenous antibiotic treatment, chemotherapy or wound care within the past 30 days of the actual infection; or underwent hemodialysis. Last, VAP includes any patient who develops pneumonia 48 to 72 hours after endotracheal intubation.

As proposed by the 2005 ATS/IDSA guidelines, the main microbiologic difference between CAP and pneumonias acquired from healthcare settings is the risk for infection with multidrug-resistant (MDR) bacteria that impairs the response to common empiric antibiotic treatment and affects the outcome. Once a patient has been diagnosed with HAP, HCAP or VAP, clinicians must immediately assess the patient's risk factors for MDR organisms, which will guide the subsequent antibiotic selection (Table 46-1).

TABLE 46-1:Risk Factors for Multidrug-Resistant Pathogens Causing Hospital-Acquired Pneumonia, Healthcare-Associated Pneumonia, and Ventilator-Associated Pneumonia

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