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.
Morita
J Y
JY
National Center for Infectious Diseases, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
Kahn
E
E
Thompson
T
T
Laclaire
L
L
Beall
B
B
Gherardi
G
G
O'Brien
K L
KL
Schwartz
B
B
D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D017963:Azithromycin / Q000008:administration & dosage*; D002353:Carrier State / Q000382:microbiology; D016009:Chi-Square Distribution; D002648:Child; D015169:Colony Count, Microbial; D016001:Confidence Intervals; D004334:Drug Administration Schedule; D004352:Drug Resistance, Microbial; D005260:Female; D006801:Humans; D008297:Male; D009305:Nasopharynx / Q000382:microbiology; D009960:Oropharynx / Q000382:microbiology; D011008:Pneumococcal Infections / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology; D013290:Streptococcal Infections / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology; D013296:Streptococcus pneumoniae / Q000187:drug effects* / Q000302:isolation & purification; D013297:Streptococcus pyogenes / Q000187:drug effects* / Q000302:isolation & purification; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents; D017963:Azithromycin