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Am Fam Physician. 2001;64(4):665

The clinical efficacy of the sputum Gram stain and sputum culture in patients with community-acquired pneumonia remains unclear. Some investigators have suggested that these tests can be used to guide management, whereas others have contended that neither test is helpful in establishing the etiology of community-acquired pneumonia. Most of the studies recommending sputum Gram stain and sputum culture have been performed in heterogeneous patient populations (i.e., patients of all ages with a variety of comorbid conditions). Theerthakarai and associates wondered if it was inappropriate to extrapolate data from heterogeneous groups to patients with simple, nonsevere community-acquired pneumonia. They studied the value of microbiologic studies in the diagnosis and management of uncomplicated community-acquired pneumonia in patients without associated comorbid factors.

Over a 12-month period, patients hospitalized for community-acquired pneumonia were screened prospectively. The diagnosis of community-acquired pneumonia was based on established criteria. Exclusion criteria included, among others, comorbid conditions, age of 65 years or older and severe pneumonia. The initial evaluation included sputum Gram stain, sputum culture and blood culture. Only patients who produced a sputum sample containing 20 or more neutrophils and fewer than 10 squamous epithelial cells were included in the study. All patients were treated with empiric antibiotics based on the American Thoracic Society guidelines.

Of the 212 patients who were screened, 74 met all criteria for inclusion in the study. Sputum Gram stains in these patients failed to identify the etiologic agent of their pneumonia, sputum cultures identified pathogens in 5 percent of the patients and all blood cultures were negative. Initial empiric antibiotic therapy was successful in all patients, and the results of the sputum Gram stains, sputum cultures and blood cultures had no clinical impact.

The authors concluded that microbiologic studies such as Gram's stain, sputum culture and blood culture have no value in patients with nonsevere community-acquired pneumonia and no comorbid conditions. None of the tests provided information that was useful in guiding the diagnosis or initial treatment of this infection. Microbiologic tests should be reserved for use in patients with moderate or severe community-acquired pneumonia or comorbid factors.

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