hi sir/madam, Thanks for your question on Healthcare Magic. Causes of acute bronchitis include viral and bacterial infections, environmental factors, and other lung conditions. Viral infection: Viruses cause 85 to 95 percent of acute bronchitis cases in adults. The same viruses that cause the common cold or flu can cause acute bronchitis. Bacterial infection: In rare cases, bacterial bronchitis can develop after a viral infection of bronchitis. This can result from infections by bacteria such as Mycoplasma pneumoniae, Chlamydia pneumoniae, and Bordetella pertussis (which causes whooping cough). Irritants: Breathing in irritants such as smoke, smog, or chemical fumes can cause inflammation in your trachea and bronchial tubes. This can lead to acute bronchitis. Other lung conditions: People with chronic bronchitis or asthma sometimes develop acute bronchitis. In these cases, acute bronchitis isn’t likely to be contagious because it’s not caused by an infection. Consult your doctor for further treatment. hope this was helpful. have a healthy day.