Fungal Infections

Rhinocerebral mucormycosis occurs most commonly in patients with uncontrolled diabetes, especially after an episode of diabetic ketoacidosis. It may also occur in leukemic patients who have had prolonged neutropenia and therapy with broad-spectrum antibiotics and occasionally in organ transplant recipients. The earliest symptoms in rhinocerebral mucormycosis are facial pain, headache, and nasal stuffiness.

P boydii is a mold that is capable of causing infection in immunosuppressed patients and less frequently in immunocompetent patients. Overall, infection with P boydii is rare.

Aspergillus spp. are capable of causing a variety of infections involving the paranasal sinuses (Table 2). Although uncommon, Aspergillus sinusitis is related to the immune status and immunologic response of the host. In the severely immunosuppressed or neutropenic patient, Aspergillus sinusitis or rhinosinusitis may occur. Symptoms include headache, toothache, nasal congestion, purulent nasal discharge, and sinus or eye pain.

Farmer’s lung, also known as extrinsic allergic alveolitis or hypersensitivity pneumonitis, is an allergic inflammatory reaction induced by inhalation of Aspergillus spores, often in exposure to mold and hay. It usually occurs after inhalation during an overwhelming exposure to spores. A multitude of other antigenic stimuli can induce a similar syndrome.

An aspergilloma of the lung may develop in individuals who have preexisting cavitary lung disease caused by conditions such as tuberculosis, sarcoidosis, silicosis, or bronchiectasis. Also known as a fungus ball or mycetoma, aspergillomas can be regarded as heavy Aspergillus colonization of the preexisting cavity. The most common symptom is hemoptysis, and, on rare occasions, severe or fatal hemoptysis can develop.

Severely immunosuppressed patients with invasive aspergillosis may be completely asymptomatic when the disease is first suspected. The initial clue may only be a positive sputum culture or an abnormal chest x-ray.

Cryptococcus neoformans exists as two distinct varieties known as variety neoformans and variety gattii (Table 1). Cryptococcus neoformans variety neoformans exists throughout the world and is found frequently in pigeon droppings that have accumulated over time. The concentrations of these organisms are often quite high in old pigeon droppings found in barns, on window ledges, and around the upper floors of old buildings. Pigeons carrying the organism do not seem to be clinically affected, and wet or fresh droppings rarely contain C neoformans.

Candida organisms are commensal with humans and, in the absence of alterations in host defense mechanisms, usually do not cause disease. Candida exists as normal flora within the oral cavity, throughout the gastrointestinal (GI) tract, in expectorated sputum, in the vagina, and in the bladder of patients with indwelling catheters. There are >150 species within the genus Candida, although the majority are not known to cause disease in humans. C albicans, C krusei, C glabrata, C tropicalis, C pseudotropicalis, C guilliermondii, C parapsilosis, C lusitaniae, and C rugosa are known human pathogens.

Candidemia may present in a variety of fashions, ranging from asymptomatic to fulminant sepsis. The candidemic patient generally has risk factors for infection, such as malignancy, chemotherapy-induced neutropenia, organ transplantation, GI surgery, burns, indwelling catheters, or exposure to broad-spectrum antibiotics. Disseminated candidiasis must be assumed to be present in those with positive blood cultures, although negative cultures do not preclude the possibility of disseminated disease. Dissemination usually manifests with many microabscesses involving multiple organs, especially the liver, spleen, and eye, but almost any organ may be involved (Box 2).