Introduction and proliferation of multidrug- resistant streptococcus pneumoniae serotype 19A clones that cause acute otitis media in an unvaccinated population

Background. Introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in the United States in 2000 was temporally associated with an increase in the incidence of disease caused by Streptococcus pneumoniae serotype 19A (Sp19A) and with increasing drug resistance within this serotype. A causative role of PCV7 was speculated. We prospectively studied the dynamics of acute otitis media (AOM) caused by Sp19A in southern Israel before the introduction of PCV7. Methods. AOMin children <5 years old undergoing tympanocentesis during 1999-2006 was studied. Antibiotic prescriptions for ̃20% of children <5 years old were recorded. Sp19A isolates were studied for antibiotic-resistance and pulsed-field gel electrophoresis patterns; multilocus sequence typing of representative isolates was compared with that of international clones. Results. Sp19A caused 438 (9.8%) of 4449 pneumococcal AOM episodes, increasing by 63.1% from 1999-2001 (mean ± SD, 8.4% ± 0.8%) to 2004-2006 (mean ± SD, 13.7% ± 0.9%) among Bedouin children, who were characterized by overcrowding and high antibiotic use. Penicillin, erythromycin, and multidrug resistance increased from <10% to 78.6%, 50.0%, and 50.0%, respectively (P < .001), and was associated with the introduction and proliferation of 2 multidrug-resistant clones that were not previously associated with multidrug resistance. This was temporally associated with the introduction of and rapid increase in azithromycin use and the frequent use of oral cephalosporins. Conclusions. The introduction and proliferation of multidrug-resistant Sp19A occurred before the introduction of PCV7. The increasing proportion of antibiotic-resistant Sp19A suggests that antibiotic use plays an important role in the community.