Prevention of antibiotic-nonsusceptible streptococcus pneumoniae with conjugate vaccines

Background. Streptococcus pneumoniae (pneumococcus) caused approximately 44000 US invasive pneumococcal disease (IPD) cases in 2008. Antibiotic nonsusceptibility complicates IPD treatment. Using penicillin susceptibility breakpoints adopted in 2008, we evaluated antibiotic-nonsusceptible IPD trends in light of the introductions of a 7-valent pneumococcal conjugate vaccine (PCV7) in 2000 and a 13-valent pneumococcal conjugate vaccine (PCV13) in 2010. Methods. IPD cases were defined by isolation of pneumococcus from a normally sterile site in individuals residing in Active Bacterial Core surveillance (ABCs) areas during 1998-2008. Pneumococci were serotyped and tested for antibiotic susceptibility using broth microdilution. Results. During 1998-2008, ABCs identified 43198 IPD cases. Penicillin-nonsusceptible strains caused 6%-14% of IPD cases, depending on age. Between 1998-1999 and 2008, penicillin-nonsusceptible IPD rates declined 64% for children aged <5 years (12.1-4.4 cases per 100000), and 45% for adults aged ≥65 (4.8-2.6 cases per 100000). Rates of IPD nonsusceptible to multiple antibiotics mirrored these trends. During 2007-2008, serotypes in PCV13 but not PCV7 caused 78%-97% of penicillin-nonsusceptible IPD, depending on age. Conclusions. Antibiotic-nonsusceptible IPD rates remain below pre-PCV7 rates for children <5 and adults ≥65 years old. PCV13 vaccines hold promise for further nonsusceptibility reductions.