Patients were considered to have a common infectious condition if the corresponding International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code appeared as the first, second, or third diagnosis for that visit (18). Diagnoses included nasopharyngitis (the common cold) or upper respiratory tract infection not otherwise specified (ICD-9-CM codes 460, 465); acute or chronic sinusitis (ICD-9-CM codes 461, 473); pharyngitis and streptococcal sore throat (ICD-9-CM codes 462, 34.0); suppurative or nonsuppurative otitis media (ICD-9-CM codes 381.0–381.4, 382); acute or acute-on-chronic bronchitis and bronchiolitis (ICD-9-CM codes 466, 490, 491.21); acute tonsillitis, laryngitis, and tracheitis (ICD-9-CM codes 463–464); bacterial or unspecified pneumonia (ICD-9-CM codes 481–483, 485–486); urinary tract infection or acute or unspecified cystitis (ICD-9-CM codes 599.0, 595.0, 595.9); cellulitis, carbuncle, or furuncle (ICD-9-CM codes 680–682); prostatitis or pelvic inflammatory disease (ICD-9-CM codes 601, 614); and sexually transmitted diseases, including syphilis, gonococcal infections, and other venereal infections (ICD-9-CM codes 90–99, 647.0–647.2). In each study period, 11% to 13% of patients who were prescribed antibiotics received a diagnosis of more than one of these infectious conditions. To prevent confusion over which disease was treated by the listed antibiotics, we excluded these patients from the diagnosis-specific analyses. Among adults with a single diagnosis of an infectious disease, there were 1657 visits for the common cold and unspecified upper respiratory tract infections, 2652 visits for sinusitis, 963 visits for pharyngitis, 908 visits for otitis media, 1674 visits for acute bronchitis, and 1636 visits for urinary tract infection over the entire study period. Among children, there were 1976 visits for the common cold and unspecified upper respiratory tract infections, 651 visits for sinusitis, 1120 visits for pharyngitis, 3107 visits for otitis media, and 625 visits for acute bronchitis.