Study to Evaluate the Efficacy and Safety of Moxifloxacin Versus Amoxicillin/Clavulanate in the Treatment of Acute Bacterial Rhinosinusitis

Inclusion Criteria: * Age \>= 18 years * Clinical diagnosis of acute rhinosinusitis with signs and symptoms present for \>/= 5-7 days but \< 28 days * Clinical diagnosis will be confirmed by nasal endoscopic examination Exclusion Criteria: * History of chronic sinusitis defined as greater than four weeks of continuous symptoms (subject with history of sinus surgery may be included; subjects with recurrent acute sinusitis may be included) * Any symptoms that suggest the subject's current illness is allergic rhinitis (e.g. repetitive sneezing, itchy nose or eyes, provocation by an allergen) and not acute bacterial sinusitis * Known bacteremia, meningitis or infection infiltrating the tissues neighboring the sinuses * Known immunodeficiency diseases including, but not limited to: neutropenia (neutrophil count \< 1000/mm3), human immunodeficiency virus (HIV) infection (Cluster of differentiation 4 (CD4)+ T-cell count of \< 200/mm3). Note: HIV testing is not required * Received systemic antibacterial therapy likely to be effective in the treatment of acute bacterial sinusitis for more than 24 hours within 5/6 days of enrollment * Requirement for concomitant systemic antibacterial therapy with agents other than those specified in this protocol * Currently receiving topical nasal corticosteroids, unless they have been on a stable dose for \> 4 weeks prior to enrollment * Requirement for concomitant therapy with systemic corticosteroids * Pregnant or breast feeding * Of childbearing potential in whom pregnancy cannot be excluded by a negative pregnancy test and who are not using reliable barrier method of contraception * Received an investigational drug in the past 30 days * Previously enrolled in this study * Unable to take oral medication * History of allergy to quinolone antibiotics or related compounds and beta-lactams * History of tendinopathy associated with quinolones * Known to have congenital or sporadic syndromes of QT interval corrected for rate (QTc) prolongation or receiving concomitant medication reported to increase the QTc interval (e.g. amiodarone, sotalol, disopyramide, quinidine, procainamide, terfenadine) * Uncorrected hypokalemia * End stage liver cirrhosis (class Child-Pugh C) * Severe renal impairment requiring dialysis * Diagnosis of rapidly fatal illness with a life expectancy of less than 6 months