Shifting Genetic Structure of Invasive Serotype 19A Pneumococci in the United States

Background. Following 7-valent conjugate vaccine introduction in the United States in 2000, invasive serotype (serol9A) pneumococcal disease (IPD) emerged rapidly. Serol9A IPD incidence increased slightly during 2005-2008 (from 2.3 cases to 2.5 cases per 100,000 population), whereas serol9A penicillin resistance (defined as a minimum inhibitor concentration [MIC] > 2 μg/mL) increased significantly (from 28.7% to 43.7%). To better understand changes, we characterized sero19A isolates recovered during 2004-2008. Methods. We performed antimicrobial susceptibility testing on all 2767 sero19A IPD isolates identified through the Centers for Disease Control Active Bacterial Core surveillance during 2004-2008. We genotyped 1804 (96.3%) of 1874 sero19A isolates recovered during 2005-2007 and all 148 year 2008 sero19A isolates from children