A 64-year-old man comes to the office due to several days of low-grade fever and productive cough. He has smoked a pack of cigarettes daily for 30 years and has been hospitalized several times for respiratory infections. Temperature is 37.2 C (99 F), blood pressure is 130/70 mm Hg, pulse is 82/min, and respirations are 14/min. Pulse oximetry shows 98% on ambient air. Lung auscultation reveals rhonchi that clear with coughing. Sputum cultures in specialized media grow round-to-oval, budding yeast, which form germ tubes when incubated at 37 C in serum. Which of the following best explains the presence of the organism in this patient's sputum sample?

Question

A 64-year-old man comes to the office due to several days of low-grade fever and productive cough.  He has smoked a pack of cigarettes daily for 30 years and has been hospitalized several times for respiratory infections.  Temperature is 37.2 C (99 F), blood pressure is 130/70 mm Hg, pulse is 82/min, and respirations are 14/min.  Pulse oximetry shows 98% on ambient air.  Lung auscultation reveals rhonchi that clear with coughing.  Sputum cultures in specialized media grow round-to-oval, budding yeast, which form germ tubes when incubated at 37 C in serum.  Which of the following best explains the presence of the organism in this patient's sputum sample?

Quizplus · Accepted Answer

This patient's 30-pack-year smoking history, low-grade fever, productive cough, normal pulse oximetry, and pulmonary rhonchi suggest a chronic obstructive pulmonary disease (COPD) exacerbation. Although expectorated sputum cultures are not routinely obtained in patients with COPD exacerbation, they may help identify the underlying respiratory pathogen in certain cases (eg, concern for drug-resistant organism). However, positive expectorated sputum results often indicate contamination with oral flora rather than true infection. This patient's sputum culture grew Candida albicans, an oval, budding yeast that forms true hyphae ("germ tubes") when incubated at body temperature (37 C). C albicans is a normal commensal of the skin and gastrointestinal tract that occasionally causes mucocutaneous infection (eg, vulvovaginitis, cutaneous candidiasis) but rarely causes invasive disease (eg, sepsis, chorioretinitis, endocarditis); invasive infection primarily occurs in those with significant neutropenia or indwelling vascular catheters (which provide a portal of entry from the skin into the bloodstream). Therefore, the presence of C albicans on a sputum sample almost always indicates contamination with oral flora rather than true infection. Other common oral contaminants (that almost never indicate true infection) include coagulase-negative staphylococci and enterococci. (Choice A) Aspergillus fumigatus, a fungus with dichotomous, branching hyphae, can colonize preexisting lung cavities, thereby creating a "fungus ball" (aspergilloma). Most aspergillomas are asymptomatic, and the organism does not resemble a yeast in culture. (Choice C) Candida infective endocarditis can cause pulmonary infection due to septic pulmonary emboli. However, this condition is rare and is typically seen in patients with indwelling vascular catheters or history of intravenous drug use. (Choice D) Histoplasma capsulatum is a dimorphic fungus that is inhaled as microconidia and converts to a small, ovoid yeast in the lungs. It replicates by forming narrow-based buds, not germ tubes. In addition, most clinically significant cases are associated with pneumonia, not bronchitis. (Choice E) Mycobacterium tuberculosis pulmonary infection is usually marked by months or years of asymptomatic latency (within granulomas) that may later reactivate and cause cavitary lung disease. Sputum culture would reveal acid-fast bacilli, not yeast. Educational objective: Expectorated sputum cultures are often contaminated by normal oral flora. The growth of Candida albicans, a normal commensal of the gastrointestinal tract and skin, almost always indicates oral contamination rather than true pulmonary infection.

A 64-Year-Old Man Comes to the Office Due to Several