Pharyngeal colonization prevalence rates for Streptococcus pyogenes and Streptococcus pneumoniae in a respiratory chemoprophylaxis intervention studyusing azithromycin

Objectives A prospective assessment of the pharyngeal colonization prevalen ce rate for Streptococcus pyrogenes and. Streptococcus pneumoniae before an d after an azithromycin chemoprophylaxis intervention clinical trial in a c ohort of US Marine Corps trainees, In addition, the minimum inhibitory conc entrations (MICs) for all streptococcal isolates, for azithromycin. penicil lin, erythromycin and cefotaxime are reported. Methods Between November 1994 and March 1995, 1108 asymptomatic male US Mar ine Corps trainees, located in Southern California, were randomly assigned to one of three intervention groups: (1) weekly oral azithromycin, 500 mg ( n = 362); (2) 1.2 MU benzathine penicillin G, intramuscularly once (n = 374 ); or (3) no chemoprophylaxis (n = 372). Subjects provided both a pre- and post-training pharyngeal culture and microbial analysis was conducted to de termine the colonization status of each study subject. Results The pretraining colonization prevalence was 1.2%:, for S, pneumonia e and 2.4% for S. pyogenes There was no statistical difference in pretraini ng prevalence between the three treatment groups for either organism. Post- training pharyngeal cultures revealed an overall prevalence of 1.1% with no difference between treatment arms. However, the overall post-training prev alence of S. pyogenes colonization increased to 4.8%, with the azithromycin group having significant evidence of protection (0.7%) in comparison with the no-treatment group (8.2%). The Etest method demonstrated no significant difference in the MIC50, MIC90, and MIC ranges between pre- and post-train ing isolates for any of the tested drugs. Conclusion The use of azithromycin as a chemoprophylactic agent to reduce t he colonization and subsequent infection of streptococcal respiratory disea se among healthy adult male military recruits may be beneficial.