Coughing up yellow pus sputum after a cold and fever may be secondary to bacterial infection or caused by bronchitis, pneumonia and other diseases. 1. Cold secondary bacterial infection: cold is caused by viral infection, early mainly clear sputum, later sputum can become thick, if combined with bacterial infection, local bacterial infection will lead to purulent lesions, the patient will have cough and symptoms of purulent sputum. 2. Bronchitis: Bronchitis will also have cold symptoms, such as cough, fever and so on. If bronchitis is caused by bacterial infection, the trachea is stimulated by inflammation and the secretion increases, which may lead to the appearance of yellow pus sputum. 2. Pneumonia: some patients with colds for a long time, easy to combine with the occurrence of pneumonia, while secondary pathogens microorganisms such as bacteria and other invasive lungs may lead to lung infections, resulting in local inflammation and increased secretion, the appearance of yellow pus sputum. There are other conditions that can cause a cold and fever will cough up yellow pus sputum, if the symptoms do not improve or aggravate, it is recommended to consult a doctor in a timely manner, to clarify the cause of the disease, standardized treatment under the guidance of the doctor, so as not to delay the condition.