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, effective antimicrobial regimen that could be used to prevent invasive GAS disease in high risk situations. To assess azithromycin as a chemoprophylactic agent, we evaluated its efficacy for eradication of oropharyngeal (OP) GAS and its impact on the nasopharyngeal (NP) colonization rate of macrolide-resistant Streptococcus pneumoniae. METHODS: We obtained OP and NP swabs for GAS and pneumococcus culture, respectively, from 300 schoolmates of a child with an invasive GAS infection. GAS 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 24 (Day 32) days post-treatment from those students identified as GAS carriers on Day 0 and determined macrolide susceptibility of GAS and pneumococcal isolates. RESULTS: Of the 300 students swabbed 152 (50%) carried GAS in their oropharynx. On Day 17, efficacy of azithromycin for GAS eradication was 95% (140 of 147) for all students. NP colonization rates for pneumococci decreased from 46% (67 of 146) to 12% (17 of 144; P < 0.001) by Day 17 and to 20% (27 of 137; P < 0.001) by Day 32. The prevalence of erythromycin-resistant pneumococcal isolates increased from 2% (3 of 146) to 4% (6 of 144) by Day 17 and to 8% (11 of 137; P = 0.04) by Day 32. CONCLUSIONS: Azithromycin is an effective short course regimen for eradication of oropharyngeal GAS. However, azithromycin selected for macrolide-resistant strains of pneumococci. These findings highlight the importance of determining the appropriate circumstances for antimicrobial prophylaxis to prevent invasive GAS infections.