Risk factors of Invasive Aspergillosis

Aspergillus species are environmental moulds which are ubiquitous. We all inhale hundreds of Aspergillus spores daily.

Above, Stained microscopy slide showing Aspergillus fumigatus in a lung alveolus

Multiple conditions can be caused by Aspergillus species and these range from invasive aspergillosis in profoundly immunocompromised patients to allergic bronchopulmonary aspergillosis in atopic individuals.

Invasive aspergillosis is a rare, although increasingly common, infection. The increase is likely due to an increasing number of patients receiving treatments which impair their immune system. Invasive aspergillosis is, by far, the most common invasive mould infection in UK hospitals. Infections caused by Fusarium species can present similarly, whereas mould infections caused by the Mucorales group are acquired and present very differently and have different risk factors.

Invasive aspergillosis is typically acquired via inhalation and thus most commonly affects the lungs. From there, it can disseminate to other organs, particularly to the brain. The disease has variable but potentially very high mortality.

Like invasive candidosis, invasive aspergillosis is often not the first diagnosis considered. A knowledge of at-risk patient groups will help guide our investigations and treatments toward those who will benefit from them.

While infections can occur in any patient, regardless of underlying immune dysfunction, there are clear risk factors for IA:

• Neutropenia is the main risk factor. Severity and duration of neutropenia correlates with the patient’s risk of infection

Other causes for immunosuppression or immunodeficiency such as:

• Immunosuppressants, corticosteroids in particular
• Solid organ transplant recipients (especially lung or heart/lung)
• Liver failure
• AIDS
• Chronic obstructive pulmonary disorder

• Chronic granulomatous disease
• Critically ill intensive care unit (ICU) patients