Impact of azithromycin on oropharyngeal carriage of Group A Streptococcus and nasopharyngeal carriage of macrolide-resistant Streptococcus pneumoniae

Background. Invasive group A streptococcal (GAS) infections are a cause of serious morbidity and high mortality. There is a need for a simple, effecti ve antimicrobial regimen that could be used to prevent invasive GAS disease in high risk situations. To assess azithromycin as a chemoprophylactic age nt, we evaluated its efficacy for eradication of oropharyngeal (OP) GAS and its impact on the nasopharyngeal (NP) colonization rate of macrolide-resis tant Streptococcus pneumoniae. Methods. We obtained OP and NP swabs for GAS and pneumococcus culture, resp ectively, from 300 schoolmates of a child with an invasive GAS infection. G AS culture-positive students were treated with daily azithromycin (12 mg/kg /day) for 5 days. We obtained follow-up OP and NP swabs at 9 (Day 17) and 2 4 (Day 32) days posttreatment from those students identified as GAS carrier s on Day 0 and determined macrolide susceptibility of GAS and pneumococcal isolates. Results. Of the 300 students swabbed 152 (50%) carried GAS in their orophar ynx. On Day 17, efficacy of azithromycin for GAS eradication was 95% (140 o f 147) for all students. NP colonization rates for pneumococci decreased fr om 46% (67 of 146) to 12% (17 of 144; P < 0.001) by Day 17 and to 20% (27 o f 137; P < 0.001) by Day 32. The prevalence of erythromycin-resistant pneum ococcal isolates increased from 2% (3 of 146) to 4% (6 of 144) by Day 17 an d to 8% (11 of 137; P = 0.04) by Day 32. Conclusions. Azithromycin is an effective short course regimen for eradicat ion of oropharyngeal GAS. However, azithromycin selected for macrolide-resi stant strains of pneumococci. These findings highlight the importance of de termining the appropriate circumstances for antimicrobial prophylaxis to-pr event invasive GAS infections.