Impact of the pneumococcal conjugate vaccine and antibiotic use on nasopharyngeal colonization by antibiotic nonsusceptible streptococcus pneumoniae, Alaska, 2000-2010

Background: We describe the relative impact of the heptavalent pneumococcal conjugate vaccine (PCV7, introduced 2001) and antibiotic use on colonization by antibiotic-resistant pneumococci in urban Alaskan children during 2000-2010. Methods: We obtained nasopharyngeal swab specimens from a convenience sample of children aged <5 years at clinics annually during 2000-2004 and 2008-2010. PCV7 status and antibiotic use <90 days before enrollment were determined by interview/medical records review. Pneumococci were characterized by serotype and susceptibility to penicillin (PCN). Isolates with full PCN resistance (PCN-R) or intermediate PCN resistance (PCN-I) were classified as PCN-NS. Results: We recruited 3496 children (median, 452 per year). During 2000-2010, a range of 18-29% per year of children used PCN/amoxicillin (P value for trend = 0.09); the proportion age-appropriately vaccinated with PCV7 increased (0-90%; P < 0.01). Among pneumococcal isolates, the PCV7-serotype proportion decreased (53-<1%; P < 0.01) and non-PCV7-serotype proportion increased (43-95%; P < 0.01). PCN-R pneumococcal colonization prevalence decreased (23-9%; P < 0.01) and PCN-I pneumococcal colonization prevalence increased (13-24%; P < 0.01); overall PCN-NS pneumococcal colonization prevalence was unchanged. PCN-NS among colonizing PCV7-type and non- PCV7-type pneumococci remained unchanged; a mean of 31% per year of PCV7-type and 10% per year of non-PCV7-type isolates were PCNR, and 10% per year of PCV7 and 20% per year of non-PCV7-type isolates were PCN-I. Conclusions: Overall, PCN-NS pneumococcal colonization remained unchanged during 2000-2010 because increased colonization by predominantly PCN-I non-PCV7 serotypes offset decreased colonization by predominantly PCN-R PCV7 serotypes. Proportion PCN-NS did not increase within colonizing pneumococcal serotype groups (PCV7 vs. non-PCV7) despite stable PCN use in our population.