Background Patterns of wheezing during early childhood may indicate differences in aetiology and prognosis of respiratory illnesses.

Objectives This study evaluated sputum cytology in infants with recurrent wheezing to classify sputum inflammatory phenotypes and assessed their characterisation over time.

Methods Sputum induction were performed in 890 infants with recurrent wheezing. Samples were classified as eosinophilic (>2.5% eosinophils), neutrophilic (>54% neutrophils), mixed granulocytic (>2.5% eosinophils, >54% neutrophils), or paucigranulocytic (≤2.5% eosinophils, ≤54% neutrophils). Sputum induction were repeated after 3 months in infants with oral montelukast sodium (4 mg, QN) or nebulizer ICS (Budesonide aerosol 0.5 mg, Bid).

Results Total 504 infants (58.1%)had raised levels of inflammatory cells, eosinophilic 30.6%, neutrophilic 65.2%, mixed granulocytic 4.2%. Variabilities in sputum inflammatory phenotype were observed in both the severe and the mild to moderate wheezing groups. Changes in phenotype were not related to inhaled ICS or oral montelukast sodium, nor were it reflected in a change in tidal pulmonary function. About 27.3% infants fulfilled the criteria for eosinophilia and there were no differences in severity even atopy between non-eosinophilic and eosinophilic wheezing.

Conclusions Raised levels of inflammatory cells were frequently found in infants with recurrent wheezing. Sputum inflammatory phenotype was not stable, unlike asthma, neutrophilic was the most common inflammatory phenotype in infants with wheezing, and it was no business of eosinophilia.