Respiratory infections and postinfectious cough: Respiratory infections caused by many pathogenic microorganisms such as Mycobacterium pertussis, Mycobacterium tuberculosis, viruses (especially respiratory syncytial virus, parainfluenza virus, cytomegalovirus), Mycoplasma pneumoniae, and Chlamydia are common causes of chronic childhood cough. Cough is a common cause, mostly in preschool children <5< span=""> years of age. Acute respiratory infections with cough symptoms lasting more than 4 weeks can be considered post-infectious cough. The mechanism may be disruption of airway epithelial integrity and/or squamification of ciliated columnar epithelial cells and/or persistent airway inflammation with temporary airway hyperresponsiveness due to the infection. The clinical features and diagnostic clues for post-infectious cough are: (1) a clear recent history of respiratory infection; (2) an irritating dry cough or a small amount of white mucous sputum; (3) no abnormalities on chest radiographs; (4) normal pulmonary ventilation; (5) the cough is usually self-limiting; and (6) other causes of chronic cough are excluded. If the cough lasts longer than 8 weeks, other diagnoses should be considered.