<prompt> Chronic cough means cough as a symptoms for-4 weeks8 weeks12 weeks16 weeks  <response>: Acute cough3 weeks is most commonly due to a respiratory tract infection,aspiration event,or inhalation of noxious chemicals or smoke.Subacute cough 3-8 weeks is frequently the residuum from a tracheobronchitis,such as in peussis or post viral tussive syndrome.Chronic cough8 weeks may be caused by a wide variety of cardiopulmonary diseases,including those of inflammatory,infectious,neoplastic,and cardiovascular etiologies.When initial assessment with chest examination and radiograph is normal,cough-variant asthma,gastroesophageal reflux,nasopharyngeal drainage,and medications ACE inhibitors are the most common causes of chronic cough. Ref:Harrisons medicine-18th edition,page no:283. 