A prospective, multi-center, observational clinical trail. Aim to evaluate the real incidence of COPD pertussis and the impact of pertussis on subaute cough.

1. Investigate the incidence and epidemiological characteristics of pertussis infection in subaute cough population.
2. To explore the relationship between pertussis infection and subaute cough.

Inclusion Criteria:

• The cough lasts 3 to 8 weeks and there is no obvious evidence of lung disease on chest X-ray.

Exclusion Criteria:

• 1. Major diseases except subaute cough; 2. Significant abnormality in laboratory examination; 3. Clinical diagnosis of lung cancer, bronchiectasis, pneumoconiosis or other simple restrictive ventilation dysfunction; 4. Patients with a history of asthma, allergic rhinitis, or a blood eosinophil count of 2600/mm3 (0.6x10^9/L) within 4 weeks; 5. Currently suffering from active tuberculosis; 6. Patients with life-threatening pulmonary embolism, or al-antitrypsin deficiency, or cystic fibrosis; 7. Patients who have undergone lung resection.

Patients with chronic cough in Shenzhen