MEDizzy - A 42-year-old HIV-positive man has had a fever and cough for

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Infectious Diseases

A 42-year-old HIV-positive man has had a fever and cough for the past month. On physical examination, his temperature is 37.5° C. On auscultation of the chest, decreased breath sounds are heard over the right posterior lung. A chest radiograph shows a large area of consolidation with a central air-fluid level involving the right middle lobe. A transbronchial biopsy specimen contains gram-positive filamentous organisms that are weakly acid-fast. His course is complicated further by empyema and acute onset of a headache. A head CT scan shows a 4-cm discrete lesion of the right hemisphere with ring enhancement. Which of the following infectious agents is most likely causing his disease?

ExplanationAlthough nocardiosis typically begins in the lungs, it often becomes disseminated, particularly to the central nervous system. These infections are most often seen in immunocompromised patients. Aspergillosis also can affect immunocompromised individuals, particularly those with neutropenia, but the fungal hyphae are easily distinguishable on hematoxylin and eosin stains. Mucor organisms have broad, nonseptate hyphae and are seen most often in patients with diabetic ketoacidosis or burn injuries. Mycobacterium avium complex infections are seen in individuals with AIDS, but these are short, acid-fast rods that produce poorly formed granulomas.