Establishing the Etiologic Diagnosis of Pneumonia
Keywords:Nosocomial, Pneumonia, Lower Airway Infections, Diagnosis
Pneumonia is a serious entity with a mortality in the U.S. of from 6-24%. Many invasive and non-invasive procedures are used to establish an etiologic diagnosis. An acceptable sputum smear is characterized by a low number of epithelial cells, higher number of leukocytes, and the presence of alveolar macrophages. A gram-stain provides good clues about pneumococcal, Klebsiella, and mixed anaerobic infections. Common problems include interpretation of streptococci as S. pneumoniae and missing H. influenzae. A culture of sputum is frequently unreliable because of contamination by the upper airway bacteria. Transtracheal aspiration can minimize the upper airway contamination. Broncho-alveolar lavage is helpful in diagnosing pneumocystis infections in AIDS patients. Double lumen catheter systems can obtain secretions from the site of pneumonia without contamination. Transbronchial biopsy provides tissue specimens for stains and cultures. Transthoracic needle aspiration provides diagnostic yield of 56 to 82% of cases with a false negative rate of 22%. Open lung biopsy is usually done in very sick, immunocompromised patients if other diagnostic procedures have been unsuccessful.
Presented at the IMA 22nd Annual Convention Orlando, Florida, July 1989. Part of Symposium: Update on the Diagnosis and Treatment of Respiratory Tract Infection.
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