Serotypes and antimicrobial susceptibilities of invasive Streptococcus pneumoniae before and after introduction of 7-valent pneumococcal conjugate vaccine, Hong Kong, 1995-2009

This study analyzed 828 isolates causing invasive pneumococcal disease (IPD) before (1995-2001, n = 265) and after (2007-2009, n = 563) the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) in Hong Kong. In children <5 years, serotype 14 had declined (36-15.7%, P < 0.01) while 19A had increased (0-12.9%, P < 0.01) in the before and after periods, respectively. In children aged <5 years, the proportion of PCV7 serotypes declined from 89.5% to 65.7% (72.8% if included cross protection against 6A) with time but that of PCV13 serotypes remained stable (91.4-93.2%). In elderly ≥65 years, 9V and 23F decreased from 3.8% to 0.3% (P = 0.01) and from 18.9% to 7.4% (P <0.01), respectively while 7F increased significantly from 0% to 4.1% (P = 0.04) over the same periods. Among isolates from aged <5 years, dual penicillin/erythromycin resistance increased from 44.1% to 64.2% (P = 0.01). The types that often had dual penicillin/erythromycin resistance were 6B, 14, 19F, 23F, 6A and 19A. The emergence of serotype 19A was associated with expansion of sequence type 320.