Role of Atypical Pathogens in the Etiology of Community-Acquired Pneumonia.

Atypical pneumonia has been described for over 100 years, but some of the pathogens attributed to it have been identified only in the past decades. The most common pathogens are , , and . The epidemiology and pathophysiology of these three pathogens have been studied since their discovery, and are reviewed herein to provide better insight when evaluating these patients, which hopefully translates into improved care. The incidence of atypical pathogens has been shown to be approximately 22% worldwide, but this probably varies with location. The history and physical exam of a patient with atypical pneumonia reveals how patients share many signs and symptoms with their counterpart patients who have typical pneumonias; therefore, the diagnosis primarily depends on laboratory identification, which is evolving and improving. What started out as simple, but difficult to yield cultures, has progressed to modern molecular-based testing assays. Treatment is missed if an empiric regimen includes only monotherapy with a β-lactam antimicrobial; so, many country guidelines, including the Infectious Diseases Society of America/American Thoracic Society guidelines for community-acquired pneumonia, recommend using a regimen containing either a macrolide or a fluorinated quinolone. Once an atypical pathogen has been identified, evidence trends toward favoring a quinolone, but more data are needed to confirm. The concept of using combination therapy in severe patients is also explored.

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