2.2 Selection criteria
The inclusion criteria was:1) a cough of >4 weeks duration; 2) cough is the main clinical manifestation; 3) aged 1-14 years old; 4) there was no abnormalities in the chest X-ray film[1].
The exclusion criteria was:1) children had abnormal chest X-ray; 2) had serious systemic diseases; and 3) unwilling/unable to cooperate with researchers to complete the questionnaire.