Allergic Bronchopulmonary Aspergillosis (ABPA)

Definition

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to the mould Aspergillus fumigatus colonising the airways. The fungus does not invade tissue; it sits in the airway mucus and provokes an exaggerated allergic and inflammatory response that progressively damages the bronchial wall. It occurs most often in people with asthma or cystic fibrosis, though COPD and bronchiectasis are now also recognised as predisposing conditions, and is best thought of as an allergic disease with an infective trigger rather than an infection.

Pathophysiology

Why some airways cannot clear the spores

Aspergillus spores are inhaled by everyone, every day, and are normally cleared by mucociliary transport and alveolar macrophages. In susceptible people — those with impaired clearance, thick mucus and an atopic immune constitution — the spores instead germinate into hyphae within airway mucus and persist. Genetic factors, including cystic fibrosis transmembrane conductance regulator variants and HLA associations, contribute to who becomes affected.¹

The allergic cascade

Persisting fungal antigen drives an exaggerated Th2 response with high total and Aspergillus-specific IgE, IgG antibody formation, and marked eosinophilic airway inflammation. The result is intense bronchial inflammation, mucus hypersecretion and the characteristic tenacious plugs. Crucially, both allergic mechanisms operate together: immediate IgE-mediated hypersensitivity and immune-complex-mediated inflammation.

From mucus plugging to bronchiectasis

Plugs obstruct segmental and subsegmental airways, causing distal collapse and, on imaging, the fleeting shadows that come and go. Over time the sustained inflammation destroys the bronchial wall, producing the pattern that most distinguishes ABPA — central bronchiectasis, affecting the proximal airways while the periphery is comparatively spared, the reverse of most other causes. Untreated, the end result can be fibrosis and irreversible loss of function.

Co-morbidities

ABPA sits on a background of asthma or cystic fibrosis and commonly coexists with atopy, allergic rhinosinusitis and allergic fungal sinusitis, nasal polyposis and, as it advances, bronchiectasis. Repeated corticosteroid courses bring their own burden — weight gain, hyperglycaemia and diabetes, osteoporosis, cataract, adrenal suppression and mood disturbance — which is a substantial part of the total morbidity and the principal reason steroid-sparing strategies matter.

Prevalence

ABPA affects roughly 1–2% of people with asthma and up to about 10% of people with cystic fibrosis, though estimates vary with the diagnostic criteria applied and rates are higher in specialist severe-asthma clinics. It is substantially under-recognised: the symptoms are those of poorly controlled asthma, and unless it is looked for the diagnosis is not made. Current guidance goes further than testing only the difficult cases — it recommends screening every adult with asthma at least once, using Aspergillus fumigatus-specific IgE in preference to skin-prick testing.²

Causes and risk factors

• Asthma — particularly long-standing, corticosteroid-dependent or difficult-to-control disease.
• Cystic fibrosis, where thick mucus and impaired clearance favour fungal colonisation.
• Atopy and a strong personal or family history of allergic disease.
• Environmental exposure — damp, mould-affected housing, compost, hay, grain, decaying vegetation and water-damaged buildings.
• Impaired mucociliary clearance from any cause, including established bronchiectasis.
• Genetic susceptibility — CFTR variants and certain HLA types.

ABPA is not contagious and is not acquired from another person — a point worth making explicitly, since the word “fungal infection” alarms people.

Symptoms

Typical features

• Asthma that is poorly controlled or deteriorating despite appropriate treatment — often the only clue.
• Cough productive of thick sputum, sometimes with brownish or dark mucus plugs, which is close to pathognomonic when present.
• Wheeze, breathlessness and chest tightness.
• Fevers, malaise and weight loss during flares.
• Occasional haemoptysis, particularly where bronchiectasis has developed.

The pattern that should prompt testing

Recurrent “chest infections” treated with repeated antibiotic and prednisolone courses that improve symptoms temporarily, in someone whose asthma was previously stable, is the classic missed presentation. Each course treats the inflammation without addressing the fungal load, so the cycle repeats.

Warning signs

Diagnosis

Why diagnosis matters

Diagnosing ABPA explains otherwise refractory asthma, allows targeted anti-inflammatory and antifungal treatment, and — the real prize — prevents progression to bronchiectasis and fibrosis. Delay is measured in irreversible airway damage, so the diagnosis is worth actively seeking rather than waiting for.²

How is it diagnosed?

Diagnosis combines a predisposing condition — or, under the revised criteria, a compatible clinical and radiological picture without one — with immunological and radiological evidence, applied against recognised criteria rather than assembled impressionistically. Demonstrating fungal sensitisation is mandatory, by Aspergillus-specific IgE in preference to skin-prick testing, together with a raised total IgE of 500 IU/mL or above and at least two of: Aspergillus-specific IgG, blood eosinophilia, or imaging consistent with ABPA.²

That IgE threshold was lowered from 1000 IU/mL in the 2024 revision, specifically to catch the diagnoses the older figure was missing, and it may sit lower again where the patient is already taking corticosteroids. A total IgE of 600 IU/mL in poorly controlled asthma is now a result worth pursuing rather than one that reassures.

Radiology

High-resolution CT is the imaging test of choice. It demonstrates central bronchiectasis, mucoid impaction — sometimes with high-attenuation mucus, which is highly specific — tree-in-bud change, and the fleeting consolidations that appear and resolve. Chest X-ray may show transient shadowing or the classic finger-in-glove sign of an impacted airway.

Blood tests and monitoring

Serial total IgE is the workhorse of monitoring: it falls with treatment response and rises before clinical relapse, which makes it a genuinely useful early-warning measure rather than a diagnostic formality. Blood eosinophilia supports the diagnosis but is suppressed by corticosteroids. A new baseline IgE is established once the patient is stable.

Lung function and microbiology

Spirometry tracks airflow obstruction and the fixed component that develops over time; gas transfer falls where fibrosis supervenes. Sputum may grow Aspergillus, though a negative culture does not exclude the diagnosis and a positive one in the absence of the immunological criteria does not make it.

Investigations for related conditions

Cystic fibrosis should be considered where ABPA presents without long-standing asthma, particularly in younger patients — sweat testing and CFTR genetics are appropriate.³ Sinus imaging is warranted where nasal symptoms suggest allergic fungal sinusitis. Chronic pulmonary aspergillosis and invasive aspergillosis are quite different diseases and are distinguished on imaging and clinical context.

Management

Management and goals

The goals are to suppress the allergic inflammation, reduce the fungal burden that drives it, clear the mucus plugs that damage airways, prevent progression to bronchiectasis and fibrosis, and achieve all of this with the least cumulative corticosteroid exposure possible. That last goal is not secondary — over a lifetime of relapsing disease, steroid toxicity can cause more harm than the ABPA.

Corticosteroids

Oral prednisolone is a first-line option for acute disease — newly diagnosed or an exacerbation — given at an adequate dose and then tapered over months against symptoms, IgE trend and imaging. Current guidance places itraconazole monotherapy alongside it rather than beneath it, and reserves the two in combination for recurrent exacerbations; asymptomatic ABPA is not routinely treated at all.² Prolonged high-dose regimens are avoided where an alternative exists.

Antifungal therapy

Itraconazole and voriconazole reduce fungal load and act as steroid-sparing agents. In a randomised trial in acute-stage ABPA complicating asthma, itraconazole monotherapy produced a lower response rate than prednisolone but with significantly fewer adverse effects — supporting its use in milder disease and as a steroid-sparing strategy rather than as a wholesale replacement.⁴ Drug levels, liver function and interactions require monitoring; itraconazole in particular raises inhaled corticosteroid exposure through CYP3A4 inhibition, which can cause iatrogenic Cushing syndrome.

Airway clearance

Mucus plugging is a mechanical problem requiring a mechanical solution. Regular airway clearance, often combined with nebulised saline or a mucolytic, clears the tenacious plugs that both obstruct airways and sustain the fungal load. This is a core treatment, not an adjunct.

Optimising the underlying disease

Asthma or cystic fibrosis care is optimised in parallel: inhaled therapy at appropriate dose with technique checked, adherence addressed, and CFTR modulator therapy where applicable. Poorly controlled underlying disease undermines every other intervention.

Identifying deterioration and relapse

Relapse is common and is signalled by a rising total IgE, returning symptoms, new radiological infiltrates or falling lung function. A doubling of IgE from the patient’s stable baseline warrants review even if they feel reasonably well, since treating early relapse prevents another increment of airway damage.

Medications

Medications for ABPA

Corticosteroids and antifungals as above, alongside optimised inhaled therapy for the underlying asthma. Nebulised saline or mucolytics support clearance.

Biologic therapy

Biologics are increasingly used in recurrent or steroid-dependent disease. Published experience with omalizumab, the anti-IgE agent, describes reduced exacerbation frequency, reduced oral corticosteroid requirement and improved lung function, although the evidence base remains largely observational rather than from large randomised trials.⁵ Anti-IL-5 and anti-IL-4/13 agents are also used in selected patients. Availability and eligibility are evolving — verify current TGA and PBS status.

Correct use of medications

Antifungal courses run for months, and adherence through a period of feeling well is the common failure point. Drug interactions are extensive: azoles interact with inhaled and intranasal corticosteroids, statins, warfarin and many others, and a formal medication review at initiation is worthwhile. Where prolonged corticosteroids are unavoidable, bone protection, glucose monitoring and adrenal considerations are managed proactively rather than reactively.

Living with ABPA

Monitoring becomes routine

Periodic IgE, lung function and clinical review become part of life. Understanding that a rising IgE means “contact the clinic” rather than “wait and see” turns monitoring from an inconvenience into a useful early-warning system the patient participates in.

A consistent airway clearance routine

Where mucus plugging is a feature, clearance is done daily rather than only during flares, timed around bronchodilators and built into an existing habit. Ten to fifteen minutes twice a day is typical.

Reducing mould exposure

Practical steps: fixing damp and leaks, ventilating bathrooms and kitchens, using extractor fans, avoiding compost turning, hay handling and disturbing decaying vegetation, wearing a P2 mask for unavoidable garden work, and treating visible mould promptly. Complete avoidance is impossible and pursuing it causes needless anxiety — the aim is reducing the load.

Managing steroid side effects

Bone density monitoring and calcium, vitamin D or bisphosphonate therapy where indicated; blood glucose monitoring; blood pressure and weight; eye review; and awareness of adrenal suppression and the need for sick-day steroid rules after prolonged courses.

Staying active

Exercise capacity is frequently reduced by both the airway disease and steroid-related myopathy and weight gain. Regular activity counters both, and resistance training specifically addresses steroid myopathy.

An action plan

A written plan naming the person’s baseline symptoms and IgE, what a flare looks like for them, and who to contact catches relapses early. Given that relapses are frequent and largely predictable, this is one of the higher-value measures to put in place.

Prognosis

With treatment most people do well and flares settle. The natural history, however, is relapsing: many patients experience repeated exacerbations over years, and a proportion become corticosteroid-dependent. Some progress to established bronchiectasis and, less commonly, to end-stage fibrosis with fixed airflow obstruction and chronic respiratory failure. Early diagnosis, IgE-guided monitoring and prompt treatment of relapse give the best chance of preventing lasting damage — which is why the diagnostic delay that is so common in this condition matters more than it might appear.

Role of the physiotherapist

Physiotherapy owns the airway side of ABPA, and in a disease defined by mucus plugging that is a substantial role. The cardiorespiratory physiotherapist teaches, reviews and progresses airway clearance — typically the active cycle of breathing technique, autogenic drainage or an oscillating PEP device, often paired with nebulised saline and timed after bronchodilator therapy. Plugs in ABPA are unusually tenacious, and technique, humidification, hydration and adequate time matter more here than in most conditions.

Where bronchiectasis has developed, the full bronchiectasis approach applies: individualised daily clearance, exacerbation recognition, and exercise as a clearance and conditioning intervention in its own right. Breathing retraining addresses the dysfunctional breathing pattern that frequently coexists with difficult asthma and is often mistaken for disease progression, and inhaler technique review at every contact is essential given how central inhaled therapy is to the underlying condition.

Physiotherapy also carries a share of the rehabilitation burden created by treatment: graded exercise and reconditioning to counter corticosteroid myopathy, weight gain and deconditioning, with resistance training specifically targeting proximal muscle weakness. And because physiotherapists see these patients regularly over long periods, they are well placed to notice the returning symptoms or rising sputum burden that precedes a documented relapse, and to prompt the IgE check that confirms it.

Part 1 · References

1. Agarwal R, Sehgal IS, Dhooria S, et al. Allergic bronchopulmonary aspergillosis. Indian J Med Res 2020;151(6):529–549.
2. Agarwal R, Sehgal IS, Muthu V, et al; ISHAM-ABPA Working Group. Revised ISHAM-ABPA working group clinical practice guidelines for diagnosing, classifying and treating allergic bronchopulmonary aspergillosis/mycoses. Eur Respir J 2024;63(4):2400061. Supersedes the 2013 ISHAM criteria.
3. Castellani C, Duff AJA, Bell SC, et al. ECFS best practice guidelines: the 2018 revision. J Cyst Fibros 2018;17(2):153–178.
4. Agarwal R, Dhooria S, Singh Sehgal I, et al. A randomised trial of itraconazole vs prednisolone in acute-stage allergic bronchopulmonary aspergillosis complicating asthma. Chest 2018;153(3):656–664.
5. Li JX, Fan LC, Li MH, Cao WJ, Xu JF. Beneficial effects of omalizumab therapy in allergic bronchopulmonary aspergillosis: a synthesis review of published literature. Respir Med 2017;122:33–42.

References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.