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1.  Postvaccination Increase in Serotype 19A Pneumococcal Disease in Norway Is Driven by Expansion of Penicillin-Susceptible Strains of the ST199 Complex 
Serotype replacement in invasive pneumococcal disease has been observed after widespread use of the 7-valent pneumococcal conjugate vaccine (PCV7). Replacement is dominated by penicillin-nonsusceptible serotype 19A in several countries. Antibiotic selection pressure has been proposed to interact with immunization, leading to rapid replacement. In Norway, where prescription of antibiotics is limited, post-PCV7 replacement by serotype 19A is dominated by penicillin-susceptible clones. Hence, serotype 19A replacement occurs, although it is not driven by antibiotic selection pressure.
doi:10.1128/CVI.05563-11
PMCID: PMC3294600  PMID: 22237889
2.  Decline in Early Childhood Respiratory Tract Infections in the Norwegian Mother and Child Cohort Study after Introduction of Pneumococcal Conjugate Vaccination 
BACKGROUND
The seven-valent pneumococcal conjugate vaccine (PCV7) was introduced into the Norwegian Childhood Immunization Program in 2006. A substantial effectiveness of PCV7 immunization against invasive pneumococcal disease has been demonstrated, while evidence of the impact on respiratory tract infections are less consistent.
METHODS
This study included children participating in the Norwegian Mother and Child Cohort Study, which recruited pregnant women between 1999 and 2008. Maternal report of acute otitis media (AOM), lower respiratory tract infections (LRTIs) and asthma in the child was compared with PCV7 immunization status, as obtained from the Norwegian Immunization Registry. Generalized linear models with the log link function were used to report adjusted relative risks (RR) and 95% confidence intervals (CI).
RESULTS
For children who had received three or more PCV7 immunizations by 12 months of age, the adjusted relative risks of AOM and LRTIs between 12 and 18 months were 0.86 [95% CI: 0.81, 0.91] and 0.78 [95% CI: 0.70, 0.87] respectively, when compared with non-immunized children. A reduced risk of AOM, RR 0.92 [95% CI: 0.90, 0.94], and LRTIs, RR 0.75 [95%CI: 0.71, 0.80], between 18 and 36 months of age was also identified among children who had received 3 or more immunizations by 18 months. No association was seen between PCV7 immunization and asthma at 36 months of age.
CONCLUSION
Reduced incidence proportions of AOM and LRTIs before 36 months of age were observed among children immunized with PCV7 through the childhood immunization program.
doi:10.1097/INF.0b013e31825d2f76
PMCID: PMC3421039  PMID: 22627867
Pneumococcal conjugate vaccination; lower respiratory tract infections; acute otitis media; asthma
3.  Recovery of Bordetella pertussis from PCR-Positive Nasopharyngeal Samples Is Dependent on Bacterial Load 
Journal of Clinical Microbiology  2012;50(12):4114-4115.
Viable Bordetella pertussis isolates are essential for surveillance purposes. We performed culture of 223 PCR-positive nasopharyngeal samples. B. pertussis was recovered from 45 (20.2%) of the samples. Growth was associated with a high bacterial load, as determined by PCR. Culture from PCR-positive samples is a feasible approach to recover B. pertussis isolates, and culture can be limited to samples with a high bacterial load.
doi:10.1128/JCM.01553-12
PMCID: PMC3502974  PMID: 23035189
4.  Impact of a Pneumococcal Conjugate Vaccination Program on Carriage among Children in Norway▿  
In July 2006, the seven-valent pneumococcal conjugate vaccine (PCV7) was introduced in Norway with a reduced (2 doses + 1 boost) dose schedule. Post-PCV7 shifts in pneumococcal reservoirs were assessed by two point prevalence studies of nasopharyngeal colonization among children in day care centers, before (2006) and after (2008) widespread use of PCV7. Nasopharyngeal swabs were obtained from 1,213 children, 611 in 2006 and 602 in 2008. A total of 1,102 pneumococcal isolates were recovered. Serotyping, multilocus sequence typing, and antimicrobial drug susceptibility testing were performed on all isolates. Although carriage of PCV7 serotypes decreased among both vaccinated and unvaccinated children, the overall prevalence of pneumococcal carriage remained high (80.4%) after vaccine introduction. The pneumococcal populations were diverse, and in the shift toward non-PCV7 serotypes, expansion of a limited number of established clonal complexes was observed. While non-antimicrobial-susceptible clones persisted among PCV7 serotypes, antimicrobial resistance did not increase among non-PCV7 serotypes. Direct and indirect protection of PCV7 against nasopharyngeal colonization was inferred from an overall decrease in carriage of PCV7 serotypes. No preference was found for nonsusceptible clones among the replacing non-PCV7 serotypes.
doi:10.1128/CVI.00435-09
PMCID: PMC2837970  PMID: 20107006
5.  Phenotypic and Genotypic Characterization of Streptococcus pneumoniae Strains Colonizing Children Attending Day-Care Centers in Norway▿  
Journal of Clinical Microbiology  2008;46(8):2508-2518.
A cross-sectional study of nasopharyngeal colonization with Streptococcus pneumoniae was performed among 573 children attending 29 day-care centers (DCCs) in Norway prior to the start of mass vaccination with the heptavalent pneumococcal conjugate vaccine (PCV-7). A sensitive sampling method was employed, including transport in an enrichment broth and serotyping of pneumococci directly from the broth, in addition to traditional single-colony isolation from blood agar plates. The prevalence of carriage was high, peaking at 88.7% in 2-year-olds. More than one serotype was isolated from 12.7% of the carriers. Of 509 isolates obtained, 227 (44.6%) belonged to the PCV-7 serotypes. Penicillin nonsusceptibility was rare (1.8% of the isolates). Nonsusceptibility to erythromycin (5.9%), clindamycin (2.0%), and tetracycline (5.5%) was associated with PCV-7 serotypes (P < 0.001). Multilocus sequence typing was performed on the whole strain collection, revealing 102 sequence types (STs), of which 31 (30.4%) were novel. Eleven isolates (2.2%) belonged to the England14-9 clone, and 19 isolates (3.7%) belonged to, or were single-locus variants of, the Portugal19F-21 clone. The pneumococcal populations within the DCCs were composed of a majority of isolates with STs shared between the DCCs and a minority of isolates with STs unique for each DCC. The highest numbers of different STs, including novel STs, were found within the most frequent serotypes. Our study indicates that carriage of S. pneumoniae is highly prevalent among children in Norwegian DCCs, with a genetically diverse pneumococcal population consisting of unique microepidemic DCC populations.
doi:10.1128/JCM.02296-07
PMCID: PMC2519506  PMID: 18524970

Results 1-5 (5)