Session: Poster Session: Non-Vaccine Type Pneumococci
Saturday, October 25, 2008: 12:00 AM
Room: Hall C
Background: Administration of the heptavalent pneumococcal conjugate vaccine (PCV7) has reduced vaccine-type (VT) invasive pneumococcal disease (IPD) in children. An increasing percentage of IPD cases is now caused by non-vaccine (NVT) serotypes. We analyzed the serotype and antimicrobial resistance patterns among S. pneumoniae (SP) responsible for IPD at Children’s Medical Center, Dallas (CMCD) from 1999 through 2007. Methods: SP isolated from normally sterile sites were collected from January 1, 1999 through December 31, 2007. Incidence of IPD was calculated using inpatient and emergency center admissions to CMCD as the denominator. SP isolated were serotyped by quellung reaction and penicillin and cefotaxime susceptibility were determined by E-test. Serotype 19A isolates were characterized by PFGE and by multi-locus sequence typing (MLST). Results: The incidence of IPD per 100,000 patients decreased 56% from 93.6 in 1999 to a nadir of 41 in 2003 (P<0.001); subsequently the rates (per 100,000 patients) were 64.2 in 2005 (p=0.039 vs 2003), 45 in 2006, and 60 in 2007. The number of IPD cases caused by serotype 19A increased 85% from 1999 through 2005 (p<0.001) at which time it comprised 20 of the 49 (41%) IPD isolates. The number of 19A isolates causing IPD decreased to 8 of 36 (22%) in 2006 but increased to 16 of 50 (32%) in 2007. As determined by MLST, the most common sequence type (ST) of the 19A isolates was ST-199, representing 35 of 71 (49.3%) isolates. In 2007 there was an increased percentage of IPD cases caused by cephalosporin resistant strains. All serotype 19A isolates in 2007 were penicillin non-susceptible. Conclusions: In Dallas, PCV7 immunization has eliminated IPD caused by VT serotypes but the overall incidence of IPD in 2007 was reduced only 36% compared with that in 1999. Many of the NVT strains are resistant to beta-lactam antibiotics.