Depends. Bronchitis is an inflammatory condition of the bronchial tubes. It can be broken down to infectious or non-infectious. Infectious causes include bacterial, viral and rarely fungal. Most commonly in an otherwise health adult, most bronchitis is viral (i.e. Untreatable with antibiotics.) non-infectious causes include allergens (pollens, molds, etc.) and irritants (smoke, chemicals, etc.).
Both. It can be due to either or. Most cases of infectious bronchitis are due to viruses though, and will not respond to antibiotics.
None. There is no good evidence that the change in season itself is causative of infection. Read more...