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Sputum cultures for the evaluation of bacterial pneumonia

Susan E Boruchoff, MD
Melvin P Weinstein, MD
Section Editor
Daniel J Sexton, MD
Deputy Editor
Sheila Bond, MD


Lower respiratory tract infections are common in the general population, occurring with increased frequency in older individuals and those with chronic diseases or compromised immune function. An etiologic diagnosis can made by culture of respiratory tract secretions, by isolation of a compatible organism from blood or pleural fluid cultures, or by molecular methods.

While a positive blood or pleural fluid culture definitively identifies the pathogen, an organism growing from a respiratory specimen is not definitive proof that it is the etiologic agent. Many bacterial species are normal flora or colonizers of the respiratory tract and, although present in respiratory secretions, they may not be responsible for the clinical illness in an individual patient with pneumonia due to another cause. As a result, there is controversy about the diagnostic accuracy of many cultures of respiratory specimens. (See "Diagnostic approach to community-acquired pneumonia in adults" and "Epidemiology, pathogenesis, microbiology, and diagnosis of hospital-acquired and ventilator-associated pneumonia in adults" and "Clinical presentation and diagnostic evaluation of ventilator-associated pneumonia".)

A rational approach to specimen collection and the interpretation of results is required if clinically useful information is to be obtained [1]. The value and limitations of sputum cultures in patients with suspected bacterial pneumonia as well as the clinical indications for obtaining sputum cultures in such patients will be reviewed here.

Issues related to specimen transport to the laboratory, general approach to Gram stain and culture, and examples of clinical microbiology findings in patients with respiratory tract infections are discussed separately. (See "Microbiology specimen collection and transport" and "Approach to Gram stain and culture results in the microbiology laboratory" and "Clinical microbiology review: Respiratory tract infections".)

The approach to the evaluation of patients with possible tuberculosis, Pneumocystis jirovecii (formerly P. carinii) pneumonia, invasive aspergillosis, influenza, and other respiratory viral infections is also discussed separately. (See "Clinical presentation and diagnosis of Pneumocystis pulmonary infection in HIV-infected patients" and "Epidemiology, clinical manifestations, and diagnosis of Pneumocystis pneumonia in HIV-uninfected patients" and "Epidemiology and clinical manifestations of invasive aspergillosis" and "Clinical manifestations of seasonal influenza in adults" and "Clinical manifestations and diagnosis of pandemic H1N1 influenza ('swine influenza')" and "Parainfluenza viruses in adults" and "Respiratory syncytial virus infection: Clinical features and diagnosis" and "Diagnosis, treatment, and prevention of adenovirus infection" and "Diagnosis of seasonal influenza in adults" and "Diagnosis of pulmonary tuberculosis in HIV-uninfected adults".)

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Literature review current through: Nov 2017. | This topic last updated: Oct 02, 2017.
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