A bad cough after a cold may be caused by untreated or incomplete treatment of the cold resulting in bacterial or viral involvement of the bronchi, causing pharyngitis, bronchitis, or pneumonia; it may also be a persistent cough caused by mycoplasma or Mycobacterium tuberculosis infection. Coughing can occur when there are excessive airway inflammatory secretions that irritate the airways. If you have a cough with sputum and sore throat after a cold, consider chronic bronchitis caused by an uncontrolled bacterial infection, and take sputum culture to identify the pathogenic bacteria and broad-spectrum antibiotics to control the disease as soon as possible. If the cough is mainly dry, it may be mycoplasma infection and can be treated with azithromycin for one week to observe the efficacy, and sputum culture is also feasible to clarify the presence of mycoplasma infection; if the cough is prolonged after a cold and accompanied by low fever, night sweats, malaise and wasting, tuberculosis bacillus infection may exist, and PPD test, sputum culture and chest X-ray are feasible to further clarify the cause before medication. Empirical anti-tuberculosis treatment is also feasible after blood collection, and if the symptoms are reduced after taking anti-tuberculosis drugs, it supports Mycobacterium tuberculosis infection. It can be seen that coughing after a cold is often due to the presence of pathogenic bacteria infection. Therefore, if you have a bad cough, you should consult the respiratory department of a regular hospital and cooperate with the doctor to perform relevant tests to identify the cause and treat it in a timely manner.