Acute bronchitis often develops three to four days after a cold or the flu. It may start with a dry cough, then after a few days the coughing spells may bring up mucus. Most people get over an acute bout of bronchitis in two to three weeks, although the cough can sometimes hang on for four weeks or more. If you’re in otherwise good health, your lungs will return to normal after you’ve recovered from the initial infection.