Thoracic fungal infections have a complex and variable presentation, ranging from benign self-limited processes, which spontaneously resolve, to severe life-threatening infections associated with disabling morbidity and high mortality. Persistent fungal infections in normal individuals may either resolve without producing symptoms, or worsen leading to severe complications of hemoptysis, mediastinal fibrosis, empyema, and meningitis. Immune-compromised hosts demonstrate greater susceptibility to fungi than normal individuals and have more severe outcomes including vascular invasion, septicemia with fungal dissemination, organ infarction, and death. Adding to this complexity, the epidemiology of fungal disease is constantly changing as species emerge or relocate or increase in virulence. Early intervention can improve survival and in some cases obviate the necessity of surgery. It is critical therefore to recognize the clinical manifestations of thoracic fungal infection early in its clinical course. Fortunately, recent advances in knowledge concerning fungal biology including the functional genome, the structure of the cell wall and membrane, and the use of molecular and epidemiologic techniques have led to rapid identification of pathogens and the institution of effective, less toxic antifungal agents.1
Infection, Transmission, Exposure
Fungi that are implicated in pulmonary pathology consist primarily of dimorphic organisms. They begin as airborne spores and later convert to yeast forms after entering the pulmonary system. The lung is a common portal of entry and represents the primary portal and site of infection in both immune-competent and immune-suppressed individuals. Opportunistic hospital-acquired infections generally arise in ICU patients with indwelling vascular or catheter instrumentation or following solid organ or hematopoietic stem cell transplantation.2 Occasionally, infection may occur by nonpulmonary portals such as cutaneous inoculation, for example, sporotrichosis. Human-to-human transmission is extremely rare and primarily occurs in the organ transplant population.
Opportunistic fungal organisms may also persist in a chronic latent state, allowing possible future activation and infection if there is compromise of the immune system. As humans are often colonized with fungal organisms, the distinction between colonization and infection may be diagnostically challenging, and outcomes from fungal infection may vary depending on the degree and extent of fungal invasion based on a balance of factors between the host and organism.
The presence of endemic fungal infection in at-risk individuals may initially be suspected by a history of travel to niche areas of fungal prevalence (Fig. 103-1).3 However, with current global travel opportunities, latent fungal reactivation can occur following distant past travel which may require extensive individual interrogation as to possible fungal exposure from prevalent areas. It is also important to remain vigilant as fungal infections can resemble or coexist with malignant disease.
Endemic niche areas for fungal prevalence. (Adapted with permission from: Hsu LY, Ng ES, Koh LP. Common and emerging fungal pulmonary infections. Infect Dis Clin North Am. 2010;24(3):557–577.)