Bacteriological and clinical efficacy of various antibiotics used in the treatment of streptococcal pharyngitis in Italy. An epidemiological study

A total of 123 community paediatricians and 23 microbiology laboratories studied the clinical and bacteriological efficacy of treatment of group A streptococcal pharyngitis in Italy. Of 1065 patients, from whom Streptococcus pyogenes was isolated, 723 returned to follow up and of these 138 (19%) still had a positive throat culture. The erythromycin resistance (ER) rate was 23.7% with resistance phenotype distribution of: 31.7% constitutive (CR), 26.6% inducible (IR) and 41.7% efflux pump (M) resistance phenotype. All strains were susceptible to the β-lactam agents tested. CR strains were highly resistant to all 14, 15 and 16 membered macrolides with the exception of rokitamycin which showed activity against 37.8% of isolates. All phenotype M and some IR isolates were susceptible to clindamycin, rokitamycin, josamycin and spiramycin; clarithromycin was active against a small percentage of strains belonging to the IR and M phenotype. Bacterial eradication was found in 85.5, 78.7 and 75.8% of the penicillin, macrolide and cephalosporin treated groups. Genotyping of strains showed that 8.7% of the 19% of cases classified as ‘failed bacterial eradication’ were due to recolonization with a different isolate, observed exclusively among β-lactams treated patients. Clinical cure was achieved in a high percentage of cases, irrespective of the antibiotic prescribed, with the best clinical efficacy being found following therapy with amoxycillin and clarithromycin (90.9%).