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Pneumonia is defined as inflammation of the pulmonary parenchyma caused by an infectious agent. In the fifth century BC, Hippocrates and his pupils first observed the cardinal symptoms of pneumonia: productive cough, fever, and dyspnea. He pioneered the use of auscultation, comparing the oscillations between the hemithoraces to diagnose lower respiratory tract infections.1 Despite millennia of medical advances, pneumonia continues to cause significant morbidity and represents the leading cause of infection-related mortality worldwide.2 Clinicians still rely primarily on history and physical examination when caring for a patient with suspected pneumonia. The clinical presentation of pneumonia is vastly heterogenous and may include fever or hypothermia; sweats; rigors (chills); pulmonary symptoms such as cough, sputum production, dyspnea, or pleurisy; and pulmonary lesions observed on radiographic examination. Nonspecific symptoms are common, including loss of appetite, fatigue, and confusion. The classic findings on physical examination include “crackles” or “rales”; however, the accuracy of clinical signs and symptoms alone have been shown to be ineffective in successfully diagnosing pneumonia.3 Radiographs assist in identifying a pulmonary lesion; however, findings may be nonspecific. Because there are no diagnostic tests available to identify the microbiologic etiology immediately upon presentation (besides those for viral causes), initial antibiotic treatment is empiric and should be started as soon as pneumonia is suspected.

Management of pneumonia is complicated by changing epidemiology. Widespread administration of the conjugate pneumococcal vaccine has significantly decreased the incidence of pneumococcal pneumonia. Additionally, there has been increased recognition of viral pathogens as molecular diagnostic tests have become more advanced.4 Viral pathogens may cause coinfections or precede a subsequent bacterial superinfection. Outbreaks of novel pathogens, such as SARS-CoV-2, pose a unique and unheralded layer of complexity to the microbiologic epidemiology of pneumonia. Despite an expanding array of antimicrobial options for treatment, none can be used empirically to treat all possible pathogens, and overuse of broad-spectrum antibiotics has led to increasing antimicrobial resistance.5 Pneumonia represents an important and demanding clinical challenge. Successful management requires synthesis of epidemiologic, clinical, laboratory, microbiologic, and radiographic data, as well as swift clinical decision-making.

The purpose of this chapter is to assist the clinician at any step of the diagnostic and treatment algorithms when caring for a patient with suspected pulmonary infection. The first portion of the chapter provides broad guidance for initial patient evaluation and establishes a basic framework for clinical assessment; common viral and bacterial pathogens are emphasized (Table 122-1). The next portion focuses on diagnostics available to the clinician, including laboratory, radiographic, and microbiologic studies. The focus is on creating a framework to assist in guiding the workup and evaluating data as they become available. The last portion of the chapter explores the details of viral, atypical, fungal, and parasitic pneumonias.

TABLE 122-1Routine Evaluation of Patients with Suspected Pneumonia

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