The incidence of invasive fungal infections has increased dramatically over the past two decades, mostly due to an increase in the number of immunocompromised patients. l -4 Patients who undergo chemotherapy for a variety of diseases, patients with organ transplants, and patients with the acquired immune deficiency syndrome have contributed most to the increase in fungal infections. s The actual incidence of invasive fungal infections in transplant patients ranges from 15% to 25% in bone marrow transplant recipients to 5% to 42% in solid organ transplant recipients. 6 ,7 The most frequently encountered are Aspergillus species, followed by Cryptococcus and Candida species. Fungal infections are also associated with a higher mortality than either bacterial or viral infections in these patient popUlations. This is because of the limited number of available therapies, dose-limiting toxicities of the antifungal drugs, fewer symptoms due to lack of inflammatory response, and the lack of sensitive tests to aid in the diagnosis of invasive fungal infections. I A study of patients with fungal infections admitted to a university-affiliated hospital indicated that communityacquired infections are becoming a serious problem; 67% of the 140 patients had community-acquired fungal pneumonia. 8 There is also an increase in nosocomial fungal infections.9Fungi are eukaryotic, unicellular to multicellular organisms that have chitinous cell walls, and reproduce asexually, sexually, or both ways. Fungal cells are larger and genomically more complex than bacteria. Their cell wall contains polysaccharides, proteins, and sugars, and their antigens are rich in complex polysaccharides and glycoproteins. Plasma membranes of fungi contain ergosterol, which is the primary target for antifungals such as amphotericin B. Although there are more than 1.3 million fungal species in the environment, only about 150 are known to be pathogenic to humans. For detailed taxonomy of the fungi, several texts are available. W-12 The virulence factors of fungi resemble those of bacteria, such as possession of a capsule, adhesion molecules, toxins, free radicals, etc.
