Interaction effect of chronic cough and ageing on increased risk of exacerbation in patients with asthma: a prospective cohort study in a real-world setting

Abstract

Background: Older adults with asthma have the greatest burden and worst outcomes, and there is increasing evidence that chronic cough (CC) is associated with asthma severity and poor prognosis. However, the clinical characteristics of older adult patients with both asthma and CC remain largely unknown.

Methods: Participants with stable asthma underwent two cough assessments within 3 months to define the presence of CC. Patients were divided into four groups based on CC and age (cut-off ≥60 years). Multidimensional assessment was performed at baseline, followed by a 12-month follow-up to investigate asthma exacerbations. Logistic regression models were used to explore the interaction effect of CC and age on asthma control and exacerbations.

Results: In total, 310 adult patients were prospectively recruited and divided into four groups: older CC group (n=46), older non-CC group (n=20), younger CC group (n=112) and younger non-CC group (n=132). Compared with the younger non-CC group, the older CC group had worse asthma control and quality of life and increased airflow obstruction. The older CC group showed an increase in moderate-to-severe exacerbations during the 12-month follow-up. There was a significant interaction effect of CC and ageing on the increased moderate-to-severe exacerbations (adjusted risk ratio 2.36, 95% CI 1.47-3.30).

Conclusion: Older asthma patients with CC have worse clinical outcomes, including worse asthma control and quality of life, increased airway obstruction and more frequent moderate-to-severe exacerbations, which can be partly explained by the interaction between CC and ageing.

FIGURE 1

Flowchart of study. ASAN: Australasian Severe Asthma Network; CC: chronic cough.

FIGURE 2

Associations of chronic cough (CC) and age with a) poorly controlled asthma at baseline, b) unscheduled visits in the 12-month follow-up, c) moderate-to-severe asthma in the 12-month follow-up and d) severe asthma exacerbation in the 12-month follow-up. Poorly controlled asthma defined as Asthma Control Questionnaire score ≥1.5. Bold text indicates statistically significant results. aOR: adjusted odds ratio; aRR: adjusted risk ratio; NA: not available. ^#: adjusted for CC, sex, body mass index (BMI), smoking, prebronchodilator forced expiratory volume in 1 s (pre-FEV₁) % predicted, inhaled corticosteroid (ICS) dosage and visual analogue scale (VAS) scores of dyspnoea, wheezing and chest tightness; ^¶: adjusted for age, sex, BMI, smoking, pre-FEV₁ % predicted, ICS dosage and VAS scores of dyspnoea, wheezing and chest tightness; ⁺: adjusted for sex, BMI, smoking, pre-FEV₁ % predicted, ICS dosage and VAS scores of dyspnoea, wheezing and chest tightness; ^§: no patients experienced future severe exacerbation in the older non-CC group; ^ƒ: the interaction effect for future severe exacerbation was not calculated.