Invasive fungal infections are associated with significant morbidity and mortality and occur most frequently in immunocompromised patients.1Candida species represent the fourth most common cause of bloodstream infections in hospitalized patients.2 Over the past decade, the field of clinical mycology has changed dramatically and there has been a doubling of licensed medications available for systemic fungal infections. Advances in medical technology, including organ and bone marrow transplantation, cytotoxic chemotherapy, the widespread use of indwelling IV catheters, and the increased use of broad-spectrum antibiotics have contributed to the increase of fungal infections.
Fungi are eukaryotic organisms that exist in two basic forms, yeasts and molds (moulds).3Figure 28-1 displays how pathogenic fungi can be grouped based on their morphological characteristics. Yeasts are unicellular in nature whereas molds are filamentous. Some fungal organisms exist in both forms and are referred to as dimorphic fungi. Dimorphic fungi exist as molds in the environment and convert to parasitic yeast in the human body. Common dimorphic fungi that cause invasive infection are Blastomyces dermatitidis, Histoplasma capsulatum, and Coccidioides immitis.3,4 Exposure to these organisms occurs in certain regions of the country and as such are termed endemic fungi.
Morphologically, pathogenic fungi can be grouped as either filamentous molds or unicellular yeasts. Molds grow as multicellular branching, thread-like filaments (hyphae) that are either septate (divided by transverse walls) or coenocytic (multinucleate without cross walls).
Reproduced with permission from: Carver PL. Invasive fungal infections. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 7th ed. New York, NY: McGraw-Hill; 2008:1973-2002.
The most common invasive fungal infections are caused by yeasts (Candida species).5 Examples of Candida species include C. albicans, C. glabrata, C. parapsilosis C. tropicalis, C. krusei, and C. lusitaniae.3,5 Candida are normal inhabitants of mucocutaneous surfaces of the human body and frequently colonize the female genital tract, gastrointestinal (GI) tract, and skin. These organisms can cause infections if they overwhelm host defenses and get into sterile areas. A classic example is seen with a proliferation in the number of Candida in the GI tract after broad-spectrum antibiotic use. Common invasive infections include bloodstream infections (candidemia) and/or invasive candidiasis (eg, peritonitis and hepato-splenic).5 Risk factors for invasive candidiasis include neutropenia, diabetes, immunodeficiency diseases, high-dose corticosteroids, immunosuppressants, antineoplastic agents, total parenteral nutrition, receipt of antibiotics, surgery, and burns.
Cryptococcus neoformans is an encapsulated yeast found in soil or bird excrement that causes invasive infections less frequently than Candida.3,6Cryptococcus neoformans most often causes meningitis and respiratory infections in immunocompromised patients.
Molds cause fewer infections than yeasts because they affect patients with severely suppressed immune systems.7 The most common molds that cause clinical infections are ...