The Center for Disease Control and Prevention (or CDCP) recommends macrolides and doxycycline for outpatient treatment of CAP while the American Thoracic Society (or ATS) divides patients into two groups dependent on the absence or presence of cardiopulmonary disease (CPD) and modifiers, with a b-lactam plus macrolide, doxycycline or fluoroquinolone recommended in the latter situation. The main differences between North American and European guidelines for outpatient treatment of CAP are that fluoroquinolones are used more in the US due to worry about penicillin-resistant pneumococcus and b-lactam resistance.