COPD and Aspergillus-a complex interaction of global health importance.

Aspergillus spp are common airborne fungi, and the commonest fungal pathogen of human lungs. In patients with chronic obstructive pulmonary disease (COPD), the usual defences against disease are impaired to various degrees, leading to persistent airway infection, especially with bronchiectasis; allergy (or sensitisation) and probable additional airways resistance; and chronic pulmonary aspergillosis or invasive aspergillosis. Recurrent COPD exacerbations are more common in those with Aspergillus found in the airways, opening up an unassessed therapeutic opportunity to reduce hospital admissions and deaths. External factors worsening the effect of this negative interaction include damp and/or mould in homes, higher air pollution indices. and respiratory viral infections that abrogate key immune defences. Corticosteroid therapy, both systemic and oral, further impairs airway and lung defences. Both local and general immune responses are affected. Aspergillus infection in patients with COPD is markedly under-recognised, primarily because the sensitivity of culture of Aspergillus from sputum is poor, bronchoscopy can be harmful in patients with chronic respiratory impariment, induced sputum is only used in research studies, and the role of serum Aspergillus IgG and antigen testing is not appreciated. In hospitalised patients and those at higher risk, high-volume fungal culture and PCR for Aspergillus on sputum would enable many more diagnoses. With approximately 60 million patients with COPD hospitalised with exacerbations globally, and high mortality rates in both invasive and chronic pulmonary aspergillosis in those with COPD, many opportunities for prevention, earlier diagnosis, and therapeutic interventions are untested. Reducing corticosteroid exposure in patients with COPD could greatly reduce the impact of Aspergillus in patients with COPD.