How is aspergillus infection acquired?

How Aspergillus Infection is Acquired

Aspergillus infection is acquired primarily by inhaling fungal spores that are ubiquitous in the environment, present in soil, water, decaying vegetation, air, and dust. 1

Primary Route of Transmission

• Inhalation of airborne spores is the dominant mechanism by which Aspergillus enters the body, distinguishing it from most bacterial pneumonias 1
• Hundreds of Aspergillus conidia (spores) are inhaled daily by everyone, but in healthy individuals these are eliminated without clinical consequences 1
• The spores remain airborne for prolonged periods and contaminate anything in contact with air 2

Environmental Sources

Community and General Environment

• Soil, water, and decaying vegetation are the primary natural reservoirs 1
• Ground surfaces, ornamental plants, flower arrangements, plant detritus, food remains, and water 1
• Gardening activities, spreading mulch or compost, and close exposure to construction or renovation sites 1

Healthcare Settings

• Unfiltered air and ventilation systems that may harbor Aspergillus spores 1
• Contaminated dust dislodged during hospital renovation and construction is a major source of nosocomial outbreaks 1
• Horizontal surfaces, food, and ornamental plants within healthcare facilities 1
• Colonization of air conduits and contaminated water systems can serve as infection sources 1
• Construction and refurbishment work in or near hospitals represents a significant risk factor 1

Less Common Routes of Acquisition

• Primary cutaneous inoculation can occur through traumatic injury, surgical intervention, contaminated adhesive dressings for venous access devices, or direct contact with macerated skin in newborns 1
• Hematogenous spread from a primary focus (usually pulmonary) can lead to disseminated disease affecting skin, bone, and other organs 1
• Burn wounds may become secondarily infected through direct environmental exposure 1

Critical Host Factors That Enable Infection

While exposure is universal, infection only develops when host defenses are compromised 1:

• Severe and prolonged granulocytopenia (especially <1,000 polymorphonuclear cells/µL) is the primary risk factor 1
• Chronic administration of corticosteroids significantly increases risk 3, 4
• Bone marrow transplant recipients, particularly allogeneic transplants with graft-versus-host disease 1
• Patients receiving chemotherapy for hematologic malignancies 1
• Preexisting structural lung disease (COPD, cystic fibrosis, inactive tuberculosis, bronchiectasis) predisposes to colonization and subsequent invasive infection 1, 5

Pathogenesis After Acquisition

• In severely immunocompromised patients, inhaled spores invade local lung tissue rather than being cleared 1
• The fungus may subsequently disseminate via bloodstream to involve multiple organs 1
• Nasopharyngeal colonization may serve as an intermediate step before invasive pulmonary disease, though this remains incompletely understood 1
• Lower respiratory tract colonization in patients with preexisting lung disease can progress to invasive infection 1

Important Clinical Caveat

Even concentrations as low as 1 CFU/m³ of airborne Aspergillus can cause infection in high-risk patients, which is why environmental control measures and protected environments with HEPA filtration are critical for severely immunocompromised individuals 1