What is the role of sputum cultures in the workup of fungal pneumonia?

Updated: Jun 21, 2019
  • Author: Romeo A Mandanas, MD, FACP; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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This study may show fungal hyphae or yeasts. However, the results must correlate with the clinical situation, because saprophytic colonization occurs in the oropharyngeal or respiratory tract of some patients and may not necessarily indicate invasive infection.

Carefully transport, process, and culture specimens that may be contaminated by bacteria, may be saprophytic yeasts endogenous to the oral cavity, and may be airborne conidia of saprophytic fungi.

The diagnosis of pulmonary cryptococcal infection is confirmed if the organism is grown in culture from sputum or BAL fluid in a patient who has clinical symptoms and radiographic finding compatible with cryptococcosis. [5]

Histoplasmosis is definitively diagnosed by growth of the organism in sputum; BAL fluid, lung tissue, or mediastinal nodes can be cultured. [5]

In pulmonary sporotrichosis, the recovery of the fungi by culture of sputum and/or positive bronchoscopy are required for diagnosis. [16]

Cultures from sputum samples collected by fiber optic bronchoscopy are not valuable for the diagnosis of pneumonia by Candida. [15] To make the diagnosis, a biopsy is required to demonstrate tissue invasion. Colonization of the respiratory tract by Candida is very frequent in critically ill patients with mechanical ventilation, but pneumonia by Candida is extremely rare because the innate defense mechanisms of the lungs make them relatively resistant to candida invasion. [15]

Scedosporium species tend to grow well on routine fungal media, but, when dealing with BAL fluid or tenacious respiratory secretions, selective media (cycloheximide or benomyl agar) are recommended for their isolation. [13]

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