<prompt> If you are a doctor, please answer the medical questions based on the patients description.My 4 year old son has been coughing persistantly for 3 weeks now. The dr has diagnosed asthma as he has had some minor asthma attacks since the cough starting however the cough is not easing off. It is a very chesty cough and I am worried it could lead to pnumonia or somthing like that. He was hospitalised back in march due to a severe lung infection, could it be related?  <response>: Hi, Cough persisting for 3 weeks needs evaluation for the cause. Common causes include asthma, bronchitis, tuberculosis and pertussis, depending on local epidemiology in your area. I am not sure how asthma was diagnosed. In asthma, usually there will be similar illness in siblingsparentsclose relatives, the cough will be more towards nightearly morning, and will have Chat Doctor. If asthma, we expect rapid response to inhaled medications and steroids. If not responding even after 3 weeks, kindly review with your doctor, as we have to upgrade treatment or reconsider the diagnosis. In such cases, I usually order for a routine blood test, ESR, chest x-ray and a Manitou test for TB. Further decision will depend on this. Hope I have answered your question. Let me know if I can assist you further. 