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Updated: May 5, 2026
Murine Model of Allergen Induced Asthma
Published on: May 14, 2012
Induced sputum: comparison of postinfectious cough with allergic asthma in children
B Zimmerman1, F S Silverman, S M Tarlo
1Gage Occupational & Environmental Health Unit, St Michael's Hospital, and the Asthma Centre, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada.
Insights
Persistent cough in children post-infection differs from asthma. Induced sputum analysis revealed significantly lower eosinophils in children with persistent cough, suggesting distinct pathophysiologic mechanisms and potentially a separate condition from allergic asthma.
Area of Science:
- Pediatric Pulmonology
- Allergy and Immunology
- Respiratory Medicine
Background:
- Persistent cough is common in children after respiratory infections and often misdiagnosed as asthma.
- The underlying pathophysiologic mechanisms of postinfectious cough and its distinction from asthma remain unclear.
Purpose of the Study:
- To investigate the inflammatory markers in induced sputum of children with persistent postinfectious cough compared to those with allergic asthma.
- To test the hypothesis that persistent postinfectious cough lacks the eosinophilic airway inflammation characteristic of allergic asthma.
Main Methods:
- Induced sputum was collected from 34 children using hypertonic saline.
- Groups included children with persistent postinfectious cough, untreated atopic asthma, and treated atopic asthma.
- Sputum eosinophil counts, peripheral blood eosinophils, serum eosinophil cationic protein, and methacholine challenge tests were analyzed.
Main Results:
- Children with persistent cough had significantly lower sputum eosinophil percentages (0.5%) compared to untreated allergic asthma (14.5%).
- Treated asthmatic children also showed lower sputum eosinophils (1.5%) than untreated asthmatics.
- Peripheral blood eosinophils and serum eosinophil cationic protein were lower in the cough group; some cough patients exhibited airway hyperresponsiveness.
Conclusions:
- Persistent postinfectious cough in children is not characterized by airway eosinophilia typical of untreated asthma.
- Some children with chronic cough demonstrate reactive airways despite the absence of eosinophilic inflammation.
- These findings suggest that postinfectious cough and allergic asthma represent distinct pathophysiologic entities in children.
Background:
Cough persisting after a respiratory infection is common in children and is often managed as asthma. However, little is known about the pathophysiologic mechanisms of such cough and how it compares with asthma.
Objective:
We used the technique of induced sputum to examine the inflammatory index values associated with persistent cough or allergic asthma in children. We hypothesized that the sputum from children with persistent postinfectious cough would differ from that of children with allergic asthma in that the former would lack eosinophils compared with the latter.
Study Design:
Sputum production was induced with hypertonic saline solution in 34 children: 12 with cough persisting for 1 month or more after an apparent respiratory tract infection, not treated with corticosteroid; 11 with untreated atopic asthma, not using inhaled corticosteroid; and 11 with treated atopic asthma using inhaled corticosteroid.
Results:
The percentage of eosinophils in the sputum of children with cough was significantly lower than in the sputum of children with untreated allergic asthma (median 0.5% vs 14.5%, P <.0001). Similarly, the percentage of eosinophils in the sputum of children with asthma treated with inhaled steroids was significantly lower compared with untreated asthmatic children (1.5% vs 14.5%, P <.0001). The peripheral blood eosinophils, serum eosinophil cationic protein, and nasal percent eosinophils of the patients with cough were also significantly lower than those from patients with untreated asthma. Methacholine challenge in 6 of the 11 cough patients tested showed mild-to-moderate hyperresponsiveness, whereas the other 5 had a negative methacholine challenge.
Conclusions:
Children with persistent postinfectious cough do not have airway eosinophilia typical of untreated asthma. Despite the absence of eosinophilic inflammation, some of the patients with chronic cough had reactive airways. These results suggest that postinfectious cough in children has different pathophysiologic features than allergic asthma and probably represents a different disease.
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