Fungal bronchitis is a distinct clinical entity which is responsive to antifungal therapy

Fungal lung disease

Fungal lung disease encompasses a wide spectrum of organisms and associated clinical conditions, presenting a significant global health challenge. The type and severity of disease are determined by underlying host immunity and infecting fungal strain. The most common group of diseases are associated with the filamentous fungus Aspergillus species and include allergic bronchopulmonary aspergillosis, sensitisation, aspergilloma and chronic and invasive pulmonary aspergillosis. Fungal lung disease remains epidemiologically heterogenous and is influenced by geography, environment and host comorbidities. Diagnostic modalities continue to evolve and now include novel molecular assays and biomarkers; however, persisting challenges include achieving rapid and accurate diagnosis, particularly in resource-limited settings, and in differentiating fungal infection from other pulmonary conditions. Treatment strategies for fungal lung diseases rely mainly on antifungal agents but the emergence of drug-resistant strains poses a substantial global threat and adds complexity to existing therapeutic challenges. Emerging antifungal agents and increasing insight into the lung mycobiome may offer fresh and personalised approaches to diagnosis and treatment. Innovative methodologies are required to mitigate drug resistance and the adverse effects of treatment. This state-of-the-art review describes the current landscape of fungal lung disease, highlighting key clinical insights, current challenges and emerging approaches for its diagnosis and treatment.

Aspergillus Serologic Findings and Clinical Outcomes in Patients With Bronchiectasis: Data From the European Bronchiectasis Registry

BACKGROUND

Aspergillus species cause diverse clinical manifestations in bronchiectasis including allergic bronchopulmonary aspergillosis (ABPA), Aspergillus sensitization (AS), and raised IgG indicating exposure to or infection with Aspergillus.

RESEARCH QUESTION

What are the prevalence and clinical significance of Aspergillus-associated conditions in individuals with bronchiectasis?

STUDY DESIGN AND METHODS

Patients with bronchiectasis enrolled into the European Bronchiectasis Registry from 2015 through 2022 with laboratory testing for Aspergillus lung disease (total IgE, IgE specific to Aspergillus or Aspergillus skin test, or IgG specific to Aspergillus and blood eosinophil counts) were included for analysis. Modified International Society for Human and Anima Mycology ABPA working group criteria (2021) were used to define ABPA.

RESULTS

Nine thousand nine hundred fifty-three patients were included. Six hundred eight patients (6.1%) were classified as having ABPA, 570 patients (5.7%) showed AS, 806 patients (8.1%) showed raised Aspergillus-specific IgG without AS, 184 patients (1.8%) showed both AS and had raised Aspergillus-specific IgG levels, and 619 patients (6.2%) demonstrated eosinophilic bronchiectasis (elevated eosinophil counts without evidence of Aspergillus lung disease). The remaining 72% showed negative Aspergillus serologic findings. Patients with ABPA, AS, or raised Aspergillus-specific IgG demonstrated more severe disease, with worse lung function and more frequent exacerbations at baseline. During long-term follow-up, patients with raised Aspergillus-specific IgG experienced higher exacerbation frequency and more severe exacerbations. AS was associated with increased exacerbations and hospitalizations only in patients not receiving inhaled corticosteroids (ICS).

INTERPRETATION

Aspergillus lung disease is common in bronchiectasis. Raised IgG levels to Aspergillus are associated with significantly worse outcomes, whereas ABPA and AS are associated with severe disease and exacerbations with a risk that is attenuated by ICS use.

Allergic fungal airways disease (AFAD): an under-recognised asthma endotype

The term allergic fungal airways disease has a liberal definition based on IgE sensitisation to thermotolerant fungi and evidence of fungal-related lung damage. It arose from a body of work looking into the role of fungi in asthma. Historically fungi were considered a rare complication of asthma, exemplified by allergic bronchopulmonary aspergillosis; however, there is a significant proportion of individuals with Aspergillus fumigatus sensitisation who do not meet these criteria, who are at high risk for the development of lung damage. The fungi that play a role in asthma can be divided into two groups; those that can grow at body temperature referred to as thermotolerant, which are capable of both infection and allergy, and those that cannot but can still act as allergens in IgE sensitised individuals. Sensitisation to thermotolerant filamentous fungi (Aspergillus and Penicillium), and not non-thermotolerant fungi (Alternaria and Cladosporium) is associated with lower lung function and radiological abnormalities (bronchiectasis, tree-in-bud, fleeting shadows, collapse/consolidation and fibrosis). For antifungals to play a role in treatment, the focus should be on fungi capable of growing in the airways thereby causing a persistent chronic allergenic stimulus and releasing tissue damaging proteases and other enzymes which may disrupt the airway epithelial barrier and cause mucosal damage and airway remodelling. All patients with IgE sensitisation to thermotolerant fungi in the context of asthma and other airway disease are at risk of progressive lung damage, and as such should be monitored closely.

New Perspectives in the Diagnosis and Management of Allergic Fungal Airway Disease

Allergy to airway-colonising, thermotolerant, filamentous fungi represents a distinct eosinophilic endotype of often severe lung disease. This endotype, which particularly affects adult asthma, but also complicates other airway diseases and sometimes occurs de novo, has a heterogeneous presentation ranging from severe eosinophilic asthma to lobar collapse. Its hallmark is lung damage, characterised by fixed airflow obstruction (FAO), bronchiectasis and lung fibrosis. It has a number of monikers including severe asthma with fungal sensitisation (SAFS) and allergic bronchopulmonary aspergillosis/mycosis (ABPA/M), but these exclusive terms constitute only sub-sets of the condition. In order to capture the full extent of the syndrome we prefer the inclusive term allergic fungal airway disease (AFAD), the criteria for which are IgE sensitisation to relevant fungi in association with airway disease. The primary fungus involved is Aspergillus fumigatus, but a number of other thermotolerant species from several genera have been implicated. The unifying mechanism involves germination of inhaled fungal spores in the lung in the context of IgE sensitisation, leading to a persistent and vigorous eosinophilic inflammatory response in association with release of fungal proteases. Most allergenic fungi, including Alternaria and Cladosporium species, are not thermotolerant and cannot germinate in the airways so only act as aeroallergens and do not cause AFAD. Studies of the airway mycobiome have shown that A. fumigatus colonises the normal as much as the asthmatic airway, suggesting it is the tendency to become IgE-sensitised that is the critical triggering factor for AFAD rather than colonisation per se. Treatment is aimed at preventing exacerbations with glucocorticoids and increasingly by the use of anti-T2 biological therapies. Anti-fungal therapy has a limited place in management, but is an effective treatment for fungal bronchitis which complicates AFAD in about 10% of cases.