Description

Aspergillosis is an infection caused by species of the mold Aspergillus. Invasive, allergic or chronic (saprophytic) disease occurs based on the immune status of the host.

• Invasive disease is seen mainly in immunocompromised patients and primarily involves the lungs, sinuses, central nervous system (CNS), or skin; rarely, endocarditis, osteomyelitis, eye/orbital disease, esophagitis, or peritonitis occurs.
• Children with asthma or cystic fibrosis may develop allergic bronchopulmonary aspergillosis (ABPA) due to a hypersensitivity reaction.
• Aspergillomas are fungal balls that grow primarily in the bronchi or lungs causing a chronic, noninvasive disease.

Epidemiology

• Aspergillus species are common, ubiquitous molds that grow on decaying vegetation and can be found in soil, plants, household dust, building material, animal droppings, and water.
• The primary route of transmission is the inhalation of aerosolized conidia or spores.
• Spores are aerosolized when soil is disturbed due to construction or gardening. Aerosolization can occur via water or ventilation systems and may result in nosocomial infections.
• Person-to-person spread does not occur.
• The incubation period is unknown.
• Risk of aspergillosis varies by the population studied.
  • ABPA occurs in 1–15% of patients with cystic fibrosis and 2.5% of adults with asthma.
  • Invasive disease is fairly rare and primarily occurs in stem cell and solid organ transplant patients.

Risk Factors

• Invasive aspergillosis occurs primarily in immunocompromised patients with prolonged neutropenia due to chemotherapy, chronic steroids or impaired phagocyte function (i.e., chronic granulomatous disease), hematologic malignancies, stem cell or solid organ transplant.
• ABPA is seen in patients with cystic fibrosis or asthma. Allergic sinusitis may be seen in children with nasal polyps or after sinus surgery.
• Aspergillomas occur in children with underlying lung disease like cystic fibrosis or tuberculosis.

General Prevention

• Hospitalized allogenic hematopoietic stem cell transplant (HSCT) patients and other high-risk immunocompromised patients like those undergoing induction chemotherapy should be placed in a protective environment.
• A protective environment should minimally be a private room isolated from construction and fresh plants. High-efficiency particulate air filtration, positive pressure, and frequent air exchanges are recommended.
• High-risk persons should avoid gardening, composting, and exposure to construction or renovation.
• As nosocomial outbreaks occur, hospitals should perform surveillance with environmental cultures as needed.

Pathophysiology

Invasive aspergillosis usually occurs when airborne spores are inhaled but not effectively cleared by alveolar macrophages and occasionally by direct invasion through damaged skin.

• Invasion of blood vessels by Aspergillus leads to infarction, necrosis, and hematogenous dissemination.
• Progression to disease depends largely on its ability to evade host defenses.
• Macrophages and neutrophils can typically eliminate Aspergillus without difficulty, explaining its rarity in normal hosts.

Etiology

Most human disease is caused by Aspergillus fumigatus. Several other species including Aspergillus flavus, Aspergillus terreus, Aspergillus versicolor, Aspergillus niger, and Aspergillus nidulan are capable of causing disease.

• Invasive aspergillosis is typically a bilateral pulmonary infection and can disseminate to the sinuses, brain, or skin. Rarer presentations include endocarditis, meningitis, osteomyelitis, esophagitis, hepatitis, peritonitis, renal or eye infections.
• Sinusitis may be acute invasive disease characterized fungal balls in the maxillary sinuses or a hypersensitivity reaction resulting in allergic fungal rhinosinusitis (AFRS).
• Cutaneous infection typically follows trauma.
• Chronic pulmonary aspergillosis may be cavitary with fungal balls or fibrotic.
• Aspergilloma are saprophytic fungus balls that grow in preexisting lung cavities due to chronic lung disease.
• ABPA is an IgE-mediated hypersensitivity response to inhaled spores.

Commonly Associated Conditions

• Hematologic malignancy
• HSCT and solid organ transplant
• Chronic granulomatous disease
• Asthma
• Cystic fibrosis