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Fungi are ubiquitous in our environment and uncommon respiratory pathogens in the immunocompetent host; they usually present with no or mild symptoms that are self-limiting. In an immunocompromised host these infections can be associated with significant morbidity and mortality.Given that most symptomatic fungal infections present with nonspecific findings, early diagnosis requires a high index of suspicion, close attention to a patient’s clinical course, and interpretation of the patient’s findings within the context of host immune status. They are categorized into two groups—those that cause endemic mycoses and those classified as opportunistic pathogens (Table 242-1). Included under endemic mycosis are two fungi, Sporothrix schenckii and Penicillium marneffei, that are not always thought of in this category but that share some similarities with others in this group. Included as an opportunistic pathogen is Pneumocystis jirovecii, an organism previously called Pneumocystic carinii and at one time thought to be protozoa.

Table 242-1. Classification of Fungal Pathogens

Endemic mycoses are geographically clustered1 as shown in Table 242-2. In cases of suspected infection, past history, including travel, is important because the organisms can remain dormant for many years. Outbreaks and clusters of cases of histoplasmosis associated with soil-disrupting activity have been described. Respiratory infections caused by opportunistic fungi generally do not occupy a geographical or ecological niche but are clustered in centers that care for the immunocompromised host. There seems to be an increase in the incidence of these infections, likely related to an increase in number of immunocompromised patients given intensive antineoplastic and immunosuppressive therapy, related improved survival, increased clinical awareness for these infections, and improved diagnostic ability. The incidence of these infections varies among centers because of factors such as differences in immunosuppressive regimens, transplants, and use of antifungal prophylaxis. For example, the incidence of pulmonary zygomycosis has been reported to be increasing in association with the increased use of voriconazole prophylaxis.2-5 Whether this increase is a result of the selective inactivity of voriconazole against zygomyces and hence the related breakthroughs, improved patient survival related to its efficacy against other known pathogens such as Aspergillus species or simply due to increasing susceptibility of the immunocompromised population is unclear.

Table 242-2. Geographic Locations of the Endemic Mycoses

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