Chapter 108: Pneumocystis Pneumonia, Candidiasis, and Other Fungal Infections

GENERAL CONSIDERATIONS

• Yeasts (e.g., Candida, Cryptococcus) appear microscopically as round, budding forms; molds (e.g., Aspergillus, Rhizopus) appear as filamentous forms called hyphae; and dimorphic fungi (e.g., Histoplasma) are spherical in tissue but appear as molds in the environment.
  • Endemic fungi (e.g., Coccidioides) are not part of the normal human microbiota and infect hosts preferentially by inhalation.
  • Opportunistic fungi (e.g., Candida and Aspergillus) invade the host from normal sites of colonization (e.g., mucous membranes or the GI tract).
• Definitive diagnosis of any fungal infection requires histopathologic identification of the fungus invading tissue and accompanying evidence of an inflammatory response.
  • Other tests that detect antigens (e.g., for Histoplasma, Cryptococcus, Aspergillus) or antibody (e.g., for Coccidioides) have different degrees of specificity and sensitivity.