Serotype replacement and multiple resistance in Streptococcus pneumoniae after the introduction of the conjugate pneumococcal vaccine.
BACKGROUND
The pneumococcal conjugate vaccine (PCV7), introduced in February 2000, covered 82% of the U.S. pediatric population in 2005. Changes over time in serogroup prevalence and multidrug-resistance (MR) to antimicrobials were evaluated using the U.S. SENTRY surveillance program.


METHODS
The study included 704 U.S. isolates, with equal numbers before (1998-1999) and after the introduction of the vaccine (2003-2004). Demographic data, serotype, and resistance profiles for five antimicrobial classes were analyzed. Strains displaying resistance to >or=2 classes were considered MR. Statistical analysis was performed using logistic regression.


RESULTS
Prevalence of PCV7 serotypes was 68.5% in the prevaccine years, dropping to 29.3% in the postvaccine period. Among PCV7 serotypes, only 19F persisted, with nonvaccine (NV) serotype 19nonF strains increasing from 3% to 20% of total p<0.001. NV serotypes were 1.9 times (95% confidence interval [CI] 1.1-3.1) more likely to acquire MR over time. Although PCV7 serotypes constituted 84% of all MR isolates in the prevaccine era, MR was unchanged in the postvaccine period due to increased prevalence and acquisition of resistance by NV serotypes. MR among invasive isolates did not change over time, but increased among noninvasive NV isolates by 17% (95% CI 12-22%).


CONCLUSIONS
The complete switch in prevalence of PCV7 by NV serotypes has been aided by a herd effect in adults and older children. NV serotypes have acquired MR at a rate that is proportional to the replacement process.
Mera
Robertino
R
GlaxoSmithKline, Research Triangle Park, North Carolina, USA. robertino.mera@gsk.com
Miller
Linda A
LA
Fritsche
Thomas R
TR
Jones
Ronald N
RN
D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002675:Child, Preschool; D024901:Drug Resistance, Multiple, Bacterial; D005260:Female; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D022401:Meningococcal Vaccines / Q000008:administration & dosage*; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000008:administration & dosage*; D011159:Population Surveillance; D015995:Prevalence; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000187:drug effects* / Q000276:immunology; D014481:United States / Q000453:epidemiology
D000900:Anti-Bacterial Agents; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022401:Meningococcal Vaccines; D022242:Pneumococcal Vaccines