The purpose of this study is to evaluate the safety and effectiveness of four oral antibiotic treatment regimens for bacterial infections in patients with chronic bronchitis. The study goals are to demonstrate that 1) levofloxacin 750 mg once daily for three days is no worse than azithromycin 250 mg twice a day for one day and then 250 mg once a day for four more days, and 2) levofloxacin 750 mg once daily for five days is no worse than amoxicillin/ clavulanate (875/125 mg) twice daily for 10 days.