Decreased Carriage and Genetic Shifts in the Streptococcus pneumoniae Population After Changing the Seven-valent to the Thirteen-valent Pneumococcal Vaccine in Norway

Serotype-specific quantification of residual free polysaccharide in multivalent pneumococcal conjugate vaccines

The Streptococcus pneumoniae bacteria has over 100 known serotypes that display a continuous change in prevalence by patients' age and geographical location and therefore necessitate continued efforts toward development of new vaccines with broader protection. Glycoconjugate vaccines have been instrumental in reducing global morbidity and mortality caused by Streptococcus pneumoniae infections. In these vaccines, the bacterial polysaccharide is conjugated to a carrier protein to enhance immunogenicity. To ensure well defined immunogenicity and stability of conjugated vaccines, reliable quantification of non-conjugated (free) polysaccharide is a critical, albeit challenging step during vaccine clinical dosing, release and stability monitoring. Multivalent preparations of Cross-reactive material 197 (CRM197)- conjugated pneumococcal polysaccharide materials often contain only nanogram levels of each individual free polysaccharide at final container concentrations. We have developed a novel method for the separation of free polysaccharides from conjugated material that requires no sample derivatization, employing instead an approach of quantitative immunoprecipitation of CRM197 with 3 different monoclonal antibodies and magnetic beads. A mix of antibodies against both linear and conformational epitopes enables successful removal of conjugates regardless of the protein folded state. The remaining free polysaccharide is subsequently measured in a serotype-specific ELISA.

Nasopharyngeal Carriage in Children After the Introduction of Generalized Infant Pneumococcal Conjugate Vaccine Immunization in Germany

Epidemiological data on nasopharyngeal (NP) bacterial carriage in children in Germany are scarce. We prospectively characterized NP colonization to evaluate the impact of pneumococcal immunization. We longitudinally collected NP swabs from 2-month-old infants (visit 1; V1) at eight representative pediatric offices 10/2008-06/2009. The second swabs were taken at age 9–12 months (V2); the third swab was taken 3–6 months after the booster vaccination at age 17–19 months (V3), and the fourth swab (V4) at age 59–61 months. Samples were broth enriched, cultured for bacteria, and isolates were serotyped. Demographic risk factors for colonization were evaluated. Among 242 vaccinees, bacterial NP carriage increased with age [from 27.2% (V1) to 70.1% (V4)]; leading isolates were S. pneumoniae, H. influenzae, M. catarrhalis, and S. pyogenes. Overall pneumococcal carriage increased [14.7% (V1), 31.5% (V2), 34.8% (V3), 42.2% (V4)], being even greater among day-care attendees. Serotype distribution changed during the study period, with vaccine serotypes declining. At visit 4, 10-valent pneumococcal conjugate vaccine (PCV10) serotypes were no longer among the NP flora, while some serotypes unique to 13-valent pneumococcal conjugate vaccine (PCV13; 3 and 19A) were found. In Germany, universal infant PCV immunization was associated with an almost complete eradication of PCV-serotypes and concomitant increase of non-PCV-serotypes, mainly 11A, 22F, and 23A.

Dose-specific Effectiveness of 7- and 13-Valent Pneumococcal Conjugate Vaccines Against Vaccine-serotype Streptococcus pneumoniae Colonization in Children

BACKGROUND

Reduced-dose pneumococcal conjugate vaccine (PCV) schedules are under consideration in countries where children are recommended to receive 3 doses. Whereas PCV-derived protection against vaccine-serotype colonization is responsible for herd effects of vaccination, dose-specific PCV effectiveness against colonization endpoints is not known. We aimed to assess the performance of differing PCV schedules against vaccine-serotype colonization in children.

METHODS

From 2009-2016, we monitored pneumococcal carriage in southern Israel, where children should receive PCV at ages 2 months, 4 months, and 12 months (2 primary [p] +1 booster [b] schedule). We analyzed nasopharyngeal swabs and vaccination histories from 5928 children aged 0-59 months without symptoms of diseases potentially attributable to pneumococci. Matching individuals on age, sex, ethnicity, visit timing, and recent antibiotic receipt, we measured schedule-specific 7-valent PCV (PCV7) and 13-valent PCV (PCV13) effectiveness against vaccine-serotype colonization in a modified case-control framework. We sampled from the distribution of all possible case-control match assignments for statistical analyses.

RESULTS

Receiving 2 primary-series PCV13 doses conferred 53% (95% confidence interval [CI], 32-67%) protection against PCV13-serotype colonization at ages ≤12 months; 1 primary-series dose was not protective. A 2p+1b PCV13 series conferred 40% (95% CI, 4-67%) and 62% (95% CI, 33-83%) protection against PCV13-serotype colonization at ages 13-24 months and 25-59 months, respectively. Estimates suggested greater PCV13-conferred protection against PCV7-targeted serotypes than the 6 PCV13-only serotypes. As compared to children receiving 2p+1b PCV13 dosing, those receiving 1p+1b and 2p+0b schedules experienced 2.05-fold (95% CI, 1.12-5.00) and 3.33-fold (95% CI, 2.28-4.93) greater odds, respectively, of vaccine-serotype pneumococcal colonization at ages 13-24 months.

CONCLUSIONS

Our results demonstrate real-world effectiveness of 2p+1b PCV dosing against vaccine-serotype colonization. Reduced-dose schedules may confer lower protection against vaccine-serotype carriage during and beyond the first year of life.

Direct and indirect effect of 10 valent pneumococcal vaccine on nasopharyngeal carriage in children under 2 years of age in Matiari, Pakistan

Background

Pakistan introduced Ten-valent pneumococcal-conjugate-vaccine PCV10 in 2012 as a 3 + 0 schedule without catch-up.

Methods

Children <2 years old in Matiari, Sindh provided nasopharyngeal swabs between 2014 and 2018, which were cultured for pneumococcus and serotyped through multiplex PCR at the Aga Khan University Hospital. Carriage rates over time for Vaccine-Type (VT) and Non-VT (NVT) serotypes were used to estimate direct, indirect, total and overall effects of vaccination. Regression analysis was used to determine factors associated with VT carriage.

Results

Pneumococcus was detected in 2370/3140 (75%). VT carriage decreased overall, 16.1–9.6% (p-trend <0.001); vaccinated (all 3 doses of PCV10 received) 11.3–8.1% (p-trend 0.031) and unvaccinated (no PCV10 dose received) 17.4–10.3% (p-trend 0.003) with a decline in serotypes 6B, 9V/9A and 19F. Immunization increased from 41.0% to 68.4% (p-trend 0.001). Direct effect of vaccine was 32.8% (95% CI 14.7–47.0%) and indirect effect 44.6%(95% CI 40.6–48.6%). Factors associated with decreased VT colonization were education 1–5 years (aOR 0.7, 95%CI 0.6–1.0), history of difficulty breathing (aOR 0.7, 95%CI 0.5–1.0), exposure to smoke (aOR 0.8, 95% CI 0.6–1.0), child fully immunized (aOR 0.7, 95%CI 0.5–1.0) and enrolled in 3rd (aOR 0.6, 95%CI 0.4–0.8) and 4th (aOR 0.6, 95%CI 0.5–0.9) year of the study whereas history of runny nose (aOR 1.5, 95% CI 1.2–1.9) was positively associated.

Conclusions

Decrease in VT pneumococcal carriage in vaccinated and unvaccinated children indicates herd immunity. Sustained increase in vaccine coverage and close long-term surveillance is warranted.

In-depth analysis of pneumococcal serotypes in Belgian children (2015-2018): Diversity, invasive disease potential, and antimicrobial susceptibility in carriage and disease

BACKGROUND

Changes in serotype distribution have been described after the switch from the 13-valent pneumococcal conjugate vaccine (PCV13) to the 10-valent pneumococcal conjugate vaccine (PCV10) in Belgium.

AIM

To describe serotype's invasive disease potential and the detailed evolution of serotype distribution and antimicrobial susceptibility of pneumococcal isolates (carriage and IPD) in children up to 30 months of age over a period during and after the vaccine switch (2015-2018).

METHODS

S. pneumoniae strains isolated from the nasopharynx of healthy children attending day-care centres (DCCs) and strains from normally sterile sites of children with IPD were serotyped (Quellung-reaction) and antimicrobial susceptibility testing was performed. Invasive disease potential was defined as the serotype-specific odds ratio (OR).

RESULTS

The highly invasive (OR > 1) serotypes 12F, 1, 3, 24A/B/F, 33F, 19A, and 9N were not frequently carried (<7.5% of carriage strains). Different serotypes dominated in carriage (23B, 23A, 11A, 15B) versus IPD (12F, 19A, 10A, 33F). PCV13 vaccine serotypes increased in carriage (5.4% (25/463) in period 1 vs 10.3% (69/668) in period 3) and in IPD (7.3% (8/110 in period 1 vs 23.9% (34/142) in period 3) due to an increase (p < 0.01) in serotype 19A. The penicillin non-susceptibility of 19A was lower (p = 0.02) in carriage (6.8%) than in IPD (23.5%). Erythromycin and tetracycline non-susceptibility were more frequent (p < 0.01) in IPD (26.0%; 23.0%) compared to carriage strains (18.2%; 14.5%) and penicillin non-susceptibility increased over the three year study period (carriage: 13.4%, 19.8%, 18.5%, p = 0.05; IPD: 11.8%, 15.0%, 20.4%, p = 0.02).

CONCLUSION

Only some of the serotypes with high invasive disease potential (serotype 1, 3, 19A) in Belgium are included in PCV10 and/or PCV13. This reinforces the need for continuous monitoring, both in healthy children as in children with IPD, to better understand the dynamics of pneumococcal disease, to optimise the composition and implementation of PCVs.

How nasopharyngeal pneumococcal carriage evolved during and after a PCV13-to-PCV10 vaccination programme switch in Belgium, 2016 to 2018

Background

The current carriage study was set up to reinforce surveillance during/after the PCV13-to-PCVC10 switch in Belgium.

Aim

This observational study monitored carriage of Streptococcus pneumoniae (Sp) serotypes, particularly those no longer covered (3, 6A, 19A), as well as Haemophilus influenzae (Hi), because PCV10 contains the non-typeable Hi protein D.

Methods

A total of 2,615 nasopharyngeal swabs from children (6–30 months old) attending day care were collected in three periods over 2016–2018. Children’s demographic and clinical characteristics and vaccination status were obtained through a questionnaire. Sp and Hi were identified by culture and PCR. Pneumococcal strains were tested for antimicrobial (non-)susceptibility by disc diffusion and serotyped by Quellung-reaction (Quellung-reaction and PCR for serotypes 3, 6A, 19A).

Results

The carriage prevalence of Sp (> 75%) remained stable over the successive periods but that of Hi increased (87.4%, 664 Hi-carriers/760 in 2016 vs 93.9%, 895/953 in 2017–2018). The proportion of non-PCV13 vaccine serotypes decreased (94.6%, 438 isolates/463 in 2016 vs 89.7%, 599/668 in 2017–2018) while that of PCV13-non-PCV10 vaccine serotypes (3 + 6A + 19A) increased (0.9%, 4 isolates/463 in 2016 vs 7.8%, 52/668 in 2017–2018), with serotype 19A most frequently identified (87.9%, 58/66 isolates). Non-susceptibility of pneumococci against any of the tested antibiotics was stable over the study period (> 44%).

Conclusions

During and after the PCV13-to-PCV10 vaccine switch, the proportion of non-PCV13 serotypes decreased, mainly due to a serotype 19A carriage prevalence increase. These results complement invasive pneumococcal disease surveillance data, providing further basis for pneumococcal vaccination programme policy making.

Antimicrobial susceptibility and clonality of Streptococcus pneumoniae isolates recovered from invasive disease cases during a period with changes in pneumococcal childhood vaccination, Norway, 2004-2016

Changes in pneumococcal antimicrobial resistance (AMR) have been reported following use of pneumococcal conjugate vaccines (PCVs) in childhood vaccination programmes. We describe AMR trends and clonality in Norway during 2004-2016; we studied 10,239 invasive pneumococcal disease (IPD) isolates in terms of serotypes, antimicrobial susceptibility, and for a systematically collected subset of 2473 isolates, multilocus sequence types (ST). The IPD cases were notified to the Norwegian Surveillance System for Communicable Diseases and pneumococcal isolates were collected through the National Reference Laboratory for Pneumococci. The cases are sourced from the entire Norwegian population. We supplemented the IPD isolates with isolates from carriage studies in children attending day-care, performed in 2006 (before mass childhood vaccination with PCV7), 2008 (2 years after PCV7 introduction), 2013 (2 years after the transition to PCV13), and 2015. IPD cases were 0-102 years old; median 64 years. Carriage study participants were typically aged 1-5 years. Overall, AMR was low; a maximum of 7% of IPD isolates were resistant, depending on the antimicrobial. Erythromycin and trimethoprim/sulfamethoxazole resistant IPD (ERY-R and SXT-R, respectively) decreased in the PCV7 period (2006-2010). In the PCV13 period (2011-2016) however, we saw an indication of increased non-susceptibility among IPD isolates. This increase was mainly due to non-vaccine serotypes 15A-ST63 (multidrug resistant), 24F-ST162 (SXT-R), 23B-ST2372 (penicillin non-susceptible and SXT-R) and 33F (ERY-R and clindamycin resistant). Resistant or non-susceptible IPD isolates were often clones introduced into Norway during the study period. The exception was ERY-R isolates; initially, these largely consisted of an established serotype 14-ST9 clone, which disappeared after introducing PCV7. The carriage study results mostly resembled the changes seen in IPD with a maximum of 9% of the participants per study carrying resistant pneumococci. As actual PCVs are not fully limiting AMR, higher-valency vaccines and prudent use of antimicrobials are still needed to temper pneumococcal AMR.

Indirect Effects of Pneumococcal Childhood Vaccination in Individuals Treated With Immunosuppressive Drugs in Ambulatory Care: A Case-cohort Study

BACKGROUND

The extent to which iatrogenically-immunosuppressed individuals benefit from indirect effects of childhood vaccination with pneumococcal conjugate vaccines (PCVs) is unknown. We determined how the sequential introduction of PCV7 (2006) and PCV13 (2011) in the Norwegian childhood vaccination program has affected the epidemiology of invasive pneumococcal disease (IPD) in individuals treated with immunosuppressants in ambulatory care.

METHODS

We conducted a case-cohort study comprising 7926 IPD cases reported to the Norwegian Surveillance System for Communicable Diseases in 2005-2014 and 249998 individuals randomly selected from the National Registry in 2012. We defined immunosuppressive treatment groups based on dispensed prescriptions retrieved from the Norwegian Prescription Database. Incidences and age-adjusted relative risks (RR) were estimated.

RESULTS

IPD incidences decreased in all groups. The PCV13 incidence decreased by 5-12% across groups. The non-PCV13 incidence increased by 4-10%, mostly in individuals on chemotherapy (overlapping 95% confidence intervals). In the PCV13 era, the RR for IPD was highest (significant) and the percentage of cases caused by the polysaccharide vaccine PPV23 serotypes lowest (numerical) in individuals on chemotherapy (RR = 20.4, PPV23 = 52%), followed by individuals on corticosteroids (RR = 6.2, PPV23 = 64%), other immunosuppressants (RR = 5.6, PPV23 = 68%), and no immunosuppressants (RR = 1 [reference], PPV23 = 74%).

CONCLUSIONS

IPD incidences declined after PCV introduction in both immunocompetent and iatrogenically-immunosuppressed individuals, underscoring the benefit of childhood vaccination for the entire population. Still, individuals treated with immunosuppressants in ambulatory care are at increased risk of IPD caused by a more diverse group of serotypes.

High residual carriage of vaccine-serotype Streptococcus pneumoniae after introduction of pneumococcal conjugate vaccine in Malawi

There are concerns that pneumococcal conjugate vaccines (PCVs) in sub-Saharan Africa sub-optimally interrupt Streptococcus pneumoniae vaccine-serotype (VT) carriage and transmission. Here we assess PCV carriage using rolling, prospective nasopharyngeal carriage surveys between 2015 and 2018, 3.6–7.1 years after Malawi’s 2011 PCV13 introduction. Carriage decay rate is analysed using non-linear regression. Despite evidence of reduction in VT carriage over the study period, there is high persistent residual carriage. This includes among PCV-vaccinated children 3–5-year-old (16.1% relative reduction from 19.9% to 16.7%); PCV-unvaccinated children 6–8-year-old (40.5% reduction from 26.4% to 15.7%); HIV-infected adults 18-40-years-old on antiretroviral therapy (41.4% reduction from 15.2% to 8.9%). VT carriage prevalence half-life is similar among PCV-vaccinated and PCV-unvaccinated children (3.26 and 3.34 years, respectively). Compared with high-income settings, there is high residual VT carriage 3.6–7.1 years after PCV introduction. Rigorous evaluation of strategies to augment vaccine-induced control of carriage, including alternative schedules and catch-up campaigns, is required.

Impact of pneumococcal conjugate vaccines (PCV) in controlling carriage needs to be evaluated to inform vaccine policy. Here, Swarthout et al. show in a prospective rolling cross-sectional study in Malawi a high residual prevalence of vaccine-serotype S. pneumoniae 7 years after PCV introduction.

Risk Factors for Carriage of Antibiotic-resistant Bacteria in Healthy Children in the Community: A Systematic Review

BACKGROUND

In addition to health care settings, antibiotic resistance has also been increasing in the community. Healthy children represent an important potential reservoir of antibiotic-resistant (AR) bacteria. However, strategies to reduce the spread of AR bacteria often fail to specifically address the factors that promote the carriage of AR bacteria in this population.The objective of this review was to Identify risk factors for carriage of AR bacteria by healthy children.

METHODS

We did a systematic search of MEDLINE, Embase and PubMed for studies in developed (OECD) countries that assessed risk factors for carriage of AR bacteria in healthy children in the community. We excluded studies done before 1998 and studies of AR Streptococcus pneumoniae carriage in the absence of pneumococcal conjugate vaccination.

RESULTS

Of 1234 studies identified, 30 were eligible for inclusion. These studies assessed the impact of 49 risk factors on AR strains of S. pneumoniae, Haemophilus influenzae, Staphylococcus aureus, Streptococcus pyogenes and Escherichia coli. The majority of these risk factors were assessed in 2 or fewer studies per bacteria. Recent antibiotic consumption was associated with carriage of resistant respiratory bacteria (S. pneumoniae, H. influenzae); however, it was not consistently associated with carriage of AR bacteria in skin or stool (S. aureus and E. coli). For AR S. aureus, transmission within households appeared to have a greater impact than individual antibiotic use.

CONCLUSIONS

The factors that promote carriage of AR bacteria by healthy children differed between bacterial species. To reduce reservoirs of AR bacteria in the community, it is essential for intervention strategies to target the specific risk factors for different bacteria.

Factors influencing PCV13 specific antibody response in Danish children starting in day care

This study examines different factors influencing the 13-valent pneumococcal conjugate vaccine (PCV13) specific antibody response in 8–13 months old Danish children starting in day care. We present secondary findings to the ProbiComp study, which included nose swabs, buccal swabs and blood samples from the children before entering day care (baseline) and again after 6 months. Pneumococci isolated from nose swabs were identified by latex agglutination kit and Quellung reaction. Luminex-based assay was used for antibody measurements against specific anti-pneumococcal capsular IgG. Buccal gene expression was analyzed by qPCR. Statistical analyses were performed in R and included Pearson’s Chi-squared test, Welch two sample t-test and linear regression models. The PCV13 antibody response was unaffected by whether the children were carriers or non-carriers of any pneumococcal serotype. Having siblings increased the risk of carrying serotype 21 before day care (p = 0.020), and having siblings increased the PCV13 antibody response at the end of study (p = 0.0135). Hepatitis B-vaccination increased the PCV13 antibody response before day care attendance (p = 0.005). The expression of IL8 and IL1B was higher in children carrying any pneumococcal serotype at baseline compared to non-carriers (p = 0.0125 and p = 0.0268 respectively).

Pneumococcal Conjugate Vaccine Breakthrough Infections: 2001-2016

BACKGROUND

Most countries use 3-dose pneumococcal conjugate vaccine (PCV) schedules; a 4-dose (3 primary and 1 booster) schedule is licensed for US infants. We evaluated the invasive pneumococcal disease (IPD) breakthrough infection incidence in children receiving 2 vs 3 primary PCV doses with and without booster doses (2 + 1 vs 3 + 1; 2 + 0 vs 3 + 0).

METHODS

We used 2001-2016 Active Bacterial Core surveillance data to identify breakthrough infections (vaccine-type IPD in children receiving ≥1 7-valent pneumococcal conjugate vaccine [PCV7] or 13-valent pneumococcal conjugate vaccine [PCV13] dose) among children aged <5 years. We estimated schedule-specific IPD incidence rates (IRs) per 100 000 person-years and compared incidence by schedule (2 + 1 vs 3 + 1; 2 + 0 vs 3 + 0) using rate differences (RDs) and incidence rate ratios.

RESULTS

We identified 71 PCV7 and 49 PCV13 breakthrough infections among children receiving a schedule of interest. PCV13 breakthrough infection rates were higher in children aged <1 year receiving the 2 + 0 (IR: 7.8) vs 3 + 0 (IR: 0.6) schedule (incidence rate ratio: 12.9; 95% confidence interval: 4.1-40.4); PCV7 results were similar. Differences in PCV13 breakthrough infection rates by schedule in children aged <1 year were larger in 2010-2011 (2 + 0 IR: 18.6; 3 + 0 IR: 1.4; RD: 16.6) vs 2012-2016 (2 + 0 IR: 3.6; 3 + 0 IR: 0.2; RD: 3.4). No differences between schedules were detected in children aged ≥1 year for PCV13 breakthrough infections.

CONCLUSIONS

Fewer PCV breakthrough infections occurred in the first year of life with 3 primary doses. Differences in breakthrough infection rates by schedule decreased as vaccine serotypes decreased in circulation.

Changes in pneumococcal carriage prevalence and factors associated with carriage in Norwegian children, four years after introduction of PCV13

Background

Streptococcus pneumoniae carriage is often asymptomatic but can cause invasive pneumococcal disease. Pneumococcal carriage is a prerequisite for disease, with children as main reservoir and transmitters. Childhood carriage can therefore be used to determine which serotypes circulate in the population and which may cause disease in the non-vaccinated population. In 2006, a pneumococcal conjugate vaccine (PCV7) was introduced into the Norwegian Childhood Immunisation Programme, which was replaced by the more valent PCV13 in 2011. We investigated changes in pneumococcal carriage prevalence 4 years after switching to PCV13 compared to three previous surveys, and analysed factors associated with carriage in children.

Methods

We conducted a cross-sectional study in Norway, autumn 2015, among children attending day-care centres. We collected questionnaire data and nasopharyngeal swabs to identify pneumococcal serotypes. We compared the carriage prevalence in 2015 with surveys conducted in the same setting performed before widespread vaccination (2006; n = 610), 2 years after PCV7 introduction (2008; n = 600), and 2 years after switching to PCV13 (2013; n = 874). Using multilevel logistic regression we determined the association between pneumococcal carriage and previously associated factors.

Results

In 2015, 896 children participated, with age ranging from 8 to 80 months. The overall carriage prevalence was 48/100 children [95%CI 44–53] in 2015, 38% [29–46] lower than in 2006 pre-PCV7, and 23% [12–32] lower than in 2013, 2 years after switching to PCV13. The PCV13 carriage prevalence was 2.8/100 children [1.9–4.2] in 2015. Increasing age (p < 0.001), recent antimicrobial use (odds ratio = 0.42 [0.21–0.57]) and being vaccinated (odds ratio = 0.37 [0.29–0.47]) were negatively associated with carriage.

Conclusions

Our study showed a continued decrease in overall pneumococcal carriage, mainly fuelled by the decline in vaccine serotypes after vaccine introduction. Childhood vaccination with PCV13 should be continued to keep low PCV13 carriage, transmission and disease. Furthermore, the low prevalence of PCV13-type carriage in children endorse the choice of not recommending PCV13 in addition to the 23-valent pneumococcal polysaccharide vaccine to most medical risk groups in Norway, as little disease caused by these serotypes can be expected.

The impact of routine childhood immunization with higher-valent pneumococcal conjugate vaccines on antimicrobial-resistant pneumococcal diseases and carriage: a systematic literature review

Introduction: The introduction of 7-valent pneumococcal conjugate vaccine (PCV7) in childhood immunization programs reduced antimicrobial-resistant pneumococcal infections by vaccine serotypes. However, emerging antimicrobial-resistant non-vaccine serotypes, particularly serotype 19A, attenuated the overall effect. In 2010, higher-valent PCVs became available containing serotypes that are prone to become antimicrobial-resistant, like serotype 7F in PCV10 and PCV13, and serotype 19A in PCV13.Areas covered: This review evaluated literature published between June 1, 2008 and June 1, 2017 reporting on the effect of PCV10 or PCV13 implementation in routine infant immunization schedules on antimicrobial-resistant invasive pneumococcal disease (IPD), otitis media (OM), and nasopharyngeal carriage (NPC) in children and adults.Expert opinion: In countries with relatively high prior pneumococcal antimicrobial resistance (AMR), PCV13 childhood vaccination programs have reduced antimicrobial-resistant IPD, OM, and NPC in children and IPD in adults. The effectiveness of PCV13 against serotype 19A is likely an important contributing factor. Only few studies have documented the impact of PCV10 on AMR. Multiple factors may influence observed decreases in pneumococcal AMR including antimicrobial stewardship, case definition, time since PCV10/13 introduction, and pre-PCV10/13 AMR levels. This review emphasizes the importance of including impact on AMR when evaluating the full public health of pneumococcal vaccination programs.

Pneumococcal carriage among children under five in Accra, Ghana, five years after the introduction of pneumococcal conjugate vaccine

Background

The study objective was to determine the carriage and serotype distribution of Streptococcus pneumoniae among children in Accra, Ghana, five years after the introduction of the pneumococcal conjugate vaccine (PCV-13) in 2012.

Methods

Nasopharyngeal swab samples were collected from 410 children below 5 years of age in Accra, Ghana, from September to December, 2016. Pneumococcal isolates were identified by optochin sensitivity and bile solubility. Serotyping was performed using the latex agglutination kit and Quellung reaction. The isolates were furthermore tested for antimicrobial susceptibility for different antimicrobials, including penicillin (PEN). Twelve isolates including seven non-typeable (NT) isolates were characterized using whole-genome sequencing analysis (WGS).

Results

The overall carriage prevalence was found to be 54% (95% CI, 49–59%), and 20% (95% CI, 49–59%) of the children were carrying PCV-13 included serotypes, while 37% (95% CI, 33–42%) of the children were carrying non-PCV-13 serotypes. Based on the serotype distribution, 33% of all observed serotypes were included in PCV-13 while 66% were non-PCV-13 serotypes. The dominating non-PCV-13 serotypes were 23B, 16F, and 11A followed by PCV-13 serotypes 23F and 19F. The PCV-13 covers the majority of resistant isolates in Accra. A proportion of 22.3% of the isolates showed intermediate resistance to penicillin G, while only one isolate showed full resistance. Forty-five isolates (20.5%) were defined as multidrug-resistant (MDR) as they were intermediate/resistant to three or more classes of antimicrobials. Of the seven NT isolates characterized by WGS, four showed highest match to genotype 38, while the remaining three showed highest match to genotype 14. Four MDR serotype 19A isolates were found to be MLST 320.

Conclusion

PCV-13 introduced in Ghana did not eliminate PCV-13 covered serotypes, and the carriage rate of 54% in this study is similar to carriage studies from pre PCV-13 period. However, the penicillin non-susceptible isolates have been reduced from 45% of carriage isolates before PCV-13 introduction to 22.3% of the isolates in this study. Continuous monitoring of serotype distribution is important, and in addition, an evaluation of an alternative vaccination schedule from 3 + 0 to 2 + 1 will be important to consider.

Electronic supplementary material

The online version of this article (10.1186/s12887-019-1690-5) contains supplementary material, which is available to authorized users.

Persistence of Nasopharyngeal Pneumococcal Vaccine Serotypes and Increase of Nonvaccine Serotypes Among Vaccinated Infants and Their Mothers 5 Years After Introduction of Pneumococcal Conjugate Vaccine 13 in The Gambia

BACKGROUND

The widespread use of pneumococcal conjugate vaccine (PCV) has brought about a dramatic decrease in pneumococci of vaccine serotypes (VTs) but nonvaccine serotypes (NVTs) have emerged.

METHODS

We conducted a cross-sectional survey (CSS) among infants who received 3 doses of 13-valent PCV (PCV13) and their mothers 5 years (CSS3) after PCV13 introduction. Nasopharyngeal swab samples were collected and cultured for isolation of Streptococcus pneumoniae. Whole-genome sequencing of the nontypeable strains was performed. Data were compared with those from 2 previous surveys conducted before PCV13 introduction (CSS1) and 1 year later (CSS2).

RESULTS

Among infants, VT carriage decreased from 33.3% (113/339) in CSS1 to 11.4% (40/351) in CSS3 (P = .001) while NVTs increased from 53.1% (180/339) in CSS1 to 74.4% (261/351) in CSS3 (P < .001). Among mothers, there was a significant decrease in VTs between CSS2 8.4% (29/347) and CSS3 5.6% (19/342) (P = .006). NVTs increased from 16.6% (55/331) in CSS1 to 32.2% (110/342) in CSS3 (P < .001). In CSS3, the most prevalent VTs were 7F in infants and 3 in mothers, and the most prevalent NVTs were serogroup 16 and nontypeables, respectively. Genomic analysis showed that VTs were more likely than NVTs to lose their ability to express the capsule.

CONCLUSIONS

Five years after PCV13 introduction, we show both direct (infants) and indirect effects (mothers) of the vaccine, while NVT replacement has occurred in both groups. Ongoing circulation of VTs warrants further study of their relevance in any consideration of a reduced dose schedule.

High Rate of Serotype Switching and Genetic Variations Indicates Widespread Recombination Between Clinical and Commensal Penicillin-Nonsusceptible Streptococcus pneumoniae in Tehran

A total of 161 Streptococcus pneumoniae were collected between 2013 and 2015 in Tehran, Iran. The strains were tested for antimicrobial susceptibility and minimum inhibitory concentrations, serotyped, and genotyped by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Penicillin-binding proteins (PBPs) were also typed by restriction fragment length polymorphism (PBP-RFLP). Out of 161 strains, 32 isolates (20%) were highly resistant to penicillin. The most frequent serotypes among the penicillin-nonsusceptible S. pneumoniae (PNSP) were 14 (24%), 23F (18%), and 19F (17%). RFLP of pbp2b, pbp2x, and pbp1a genes revealed 8, 6, and 7 different patterns, respectively. Analysis of 93 PNSP isolates displayed 80 PFGE types with 8 common types constituting 21 (23%) isolates. The remaining 72 isolates (77%) were single types. MLST indicated a high degree of genetic diversity among the 93 PNSP with 36 different sequence types. Six internationally known penicillin resistant clones were identified in our isolates among which Spain^23F-1 (ST81), Spain^6B-2 (ST90), and Spain^9V-3 (ST156) were the predominant clones. The results indicated international identifiable clones of S. pneumoniae, especially Spain^23F-1 with high penicillin resistance could play a major role in spread of antimicrobial resistance in Iran. The extensive sequence variation in PBP2x, PBP2b, and PBP1a in resistant strains of clinical and commensal S. pneumoniae was suggestive of a widespread homologous recombination within S. pneumoniae populations.

Follow-up of serotype distribution and antimicrobial susceptibility of Streptococcus pneumoniae in child carriage after a PCV13-to-PCV10 vaccine switch in Belgium

BACKGROUND

A three year pneumococcal carriage study was set up in Belgium when the vaccination programme switched from a 13-valent (PCV13) to a 10-valent (PCV10) vaccine. We compared the first follow-up period (October 2016 - June 2017, year 2, Y2) for nasopharyngeal carriage, serotype distribution and antimicrobial susceptibility of S. pneumoniae with the baseline (January-July 2016, year 1, Y1).

MATERIALS/METHODS

A single nasopharyngeal swab was taken in children (6-30 months), either attending one of the 112 day-care centres (DCCs), or visiting one of the 21 physicians for an acute otitis media (AOM). S. pneumoniae were cultured, screened for antimicrobial susceptibility, and serotyped.

RESULTS

In Y2, 1218 samples were collected. The majority of the Y2-children (>85%) was vaccinated appropriately for their age. Children in Y2 received either PCV13 only (DCC: 23.5%; AOM: 24.6%), PCV10 only (DCC: 29.8%; AOM: 37.7%), or a mix of both vaccines (DCC: 31.9%; AOM: 25.4%). Pneumococcal carriage rates were high (Y2, DCC: 68.2%; AOM: 64.8%). Among carriers, prevalence of PCV13 serotypes was low (Y2 vs Y1, DCC: 3.5% vs 5.4%; AOM: 7.6% vs 7.7%). Although prevalence of PCV13-non-PCV10 serotypes did not increase significantly compared to Y1 (Y2 vs Y1, DCC: 1.6% vs 0.9%; Y2 vs Y1, AOM: 5.1% vs 0.0%), the proportion of serotypes 3, 6A, 19A among PCV13 serotype carriers in DCC was significantly higher in Y2 (46.2% vs Y1: 16.0%, p-value = 0.034). Serotypes 23B and 15B were the predominant non-vaccine serotypes (Y2). Among detected strains, non-susceptibility to at least one of five antibiotics tested (penicillin, tetracycline, erythromycin, levofloxacin, cotrimoxazole) was comparable to Y1 (Y2 vs Y1, DCC: 41.3% vs 42.4%; AOM: 49.4% vs 48.1%).

CONCLUSION

After completion of the PCV13-to-PCV10 vaccine switch in Belgium, the proportion of PCV13-non-PCV10 serotypes (mainly 19A) significantly increased among PCV13 serotype carriers in DCC, stressing the need for strengthened surveillance as the PCV10-vaccinated population grows.

Probiotics and carriage of Streptococcus pneumoniae serotypes in Danish children, a double-blind randomized controlled trial

This study examined the carriage of Streptococcus pneumoniae in healthy Danish children aged 8–19 months and assessed the effect of the probiotics Lactobacillus rhamnosus GG and Bifidobacterium animalis subsp lactis on the pneumococcal carriage during daycare enrolment. Potential risk factors of pneumococcal carriage were analysed and the carriage study was compared with registered invasive pneumococcal disease (IPD) data. This study is a part of the ProbiComp study, which was a double-blind, randomized controlled trial, including 290 children allocated to probiotics or placebo for 6 months and recruited during two autumn seasons (2014/2015). Pneumococci were identified by optochin sensitivity, bile solubility, α-hemolysis and/or capsular reaction. Serotyping was performed by latex agglutination kit and Quellung reaction. The carriage rate of S. pneumoniae was 26.0% at baseline and 67.4% at the end of intervention. No significant difference was observed between the placebo group and the probiotics group (p = 0.508). Children aged 8–19 months were carriers of non-pneumococcal vaccine serotypes causing IPD in children aged 0–4 years. However, serotypes causing most IPD cases in Danish elderly were either not found or found with low prevalence suggesting that children are not the main reservoir of those serotypes and other age groups need to be considered as carriers.

Distribution of serotypes and patterns of antimicrobial resistance among commensal Streptococcus pneumoniae in nine European countries

Background

Streptococcus pneumoniae is a commensal of the human upper respiratory tract and a major cause of morbidity and mortality worldwide. This paper presents the distribution of serotypes and antimicrobial resistance in commensal S. pneumoniae strains cultured from healthy carriers older than four years of age in nine European countries.

Methods

Nasal swabs from healthy persons (age between 4 and 107 years old) were obtained by general practitioners from each country from November 2010 to August 2011. Swabs were cultured for S. pneumoniae using a standardized protocol. Antibiotic resistance was determined for isolated S. pneumoniae by broth microdilution. Capsular sequencing typing was used to identify serotypes, followed by serotype-specific PCR assays in case of ambiguous results.

Results

Thirty-two thousand one hundred sixty-one nasal swabs were collected from which 937 S. pneumoniae were isolated. A large variation in serotype distribution and antimicrobial resistant serotypes across the participating countries was observed. Pneumococcal vaccination was associated with a higher risk of pneumococcal colonization and antimicrobial resistance independently of country and vaccine used, either conjugate vaccine or PPV 23).

Conclusions

Serotype 11A was the most common in carriage followed by serotypes 23A and 19A. The serotypes showing the highest resistance to penicillin were 14 followed by 19A. Serotype 15A showed the highest proportion of multidrug resistance.

Electronic supplementary material

The online version of this article (10.1186/s12879-018-3341-0) contains supplementary material, which is available to authorized users.

Longitudinal characterization of nasopharyngeal colonization with Streptococcus pneumoniae in a South African birth cohort post 13-valent pneumococcal conjugate vaccine implementation

Monitoring changes in pneumococcal carriage is key to understanding vaccination-induced shifts in the ecology of carriage and impact on health. We longitudinally investigated pneumococcal carriage dynamics in infants. Pneumococcal isolates were obtained from nasopharyngeal (NP) swabs collected 2-weekly from 137 infants enrolled from birth through their first year of life. Pneumococci were serotyped by sequetyping, confirmed by Quellung. Pneumococci were isolated from 54% (1809/3331) of infants. Median time to first acquisition was 63 days. Serotype-specific acquisition rates ranged from 0.01 to 0.88 events/child-year and did not differ between PCV13 and non-PCV13 serotypes (0.11 events/child-year [95% CI 0.07-0.18] vs. 0.11 events/child-year [95% CI 0.06-0.18]). There was no difference in carriage duration between individual PCV13 and non-PCV13 serotypes (40.6 days [95% CI 31.9-49.4] vs. 38.6 days [95% CI 35.1-42.1]), however cumulatively the duration of carriage of non-PCV13 serotypes was greater than PCV13 serotypes (141.2 days (95% CI 126.6-155.8) vs. 30.7 days (95% CI 22.3-39.0). Frequently carried PCV13 serotypes included 19F, 9V, 19A and 6A, while non-PCV13 serotypes included 15B/15C, 21, 10A, 16F, 35B, 9N and 15A. Despite high immunization coverage in our setting, PCV13 serotypes remain in circulation in this cohort, comprising 22% of isolates. Individual PCV13 serotypes were acquired, on average, at equivalent rate to non-PCV13 serotypes, and carried for a similar duration, although the most common non-PCV13 serotypes were more frequently acquired than PCV13 serotypes.

Streptococcus pneumoniae: Antimicrobial Resistance and Serotypes of Strains Carried by Children and Causing Invasive Disease in the Faroe Islands

Knowledge about pneumococcal carriage, antibacterial resistance, serotype prevalence, and prevalence of invasive pneumococcal disease (IPD) after introduction of pneumococcal conjugate vaccines (PCVs) is lacking in the Faroe Islands. PCV-7 was introduced in 2008 and PCV-13 in 2010. The aim was to obtain knowledge on serotypes and antimicrobial resistance in pneumococci from carriage in children attending day-care centers (DCCs) and invasive isolates. Nasopharyngeal swabs were collected from 607 healthy children attending DCCs in the Faroe Islands in January to March in 2009, 2010, and 2011. Pneumococci were cultured selectively, tested for antibacterial susceptibility, and serotyped. Data from IPD isolates from 1974 to 2016 from the Department of Microbiology, National Hospital of the Faroe Islands, and typed and stored at Staten Serum Institute were also analyzed. Of the 607 screened children, 45% were pneumococcal carriers, 50% in 2009, 40% in 2010, and 42% in 2011. Antibiotic resistance in pneumococci was rare both in carriers and patients. Five penicillin nonsusceptible pneumococci were found in carriers (1.8%) and one among the invasive isolates (1.7%). The most common serotypes in carriage were 6B and 6A in 2009, serotype 3 and 6C in 2010, and serotype 11 and 6C in 2011. Serotype 6B was not found in 2011. The most common serotypes among IPD were 7F and 3. Pneumococcal carriage prevalence in healthy children attending DCCs in the Faroe Islands was low and antibacterial resistance was rare, compared with Iceland. The results suggest a possible serotype shift, reduction in antibacterial use, and PCV-7/13 serotype decrease in IPD after the introduction of pneumococcal vaccinations in children.

Pneumococcal whole-cell and protein-based vaccines: changing the paradigm

INTRODUCTION

Epidemiologic evaluations of Streptococcus pneumoniae nasopharyngeal (NP) colonization and pneumococcal disease suggest that newer serotypes in future formulations of pneumococcal conjugate vaccines (PCVs) are needed and there may need to be continued reformulations because there are many new emerging serotypes expressed by pneumococci. Areas covered: Mechanisms of protection by next-generation whole-cell vaccine (WCV) and/or multi-component pneumococcal purified protein vaccines (PPVs) in development for prevention of pneumococcal infections. Expert commentary: A long-term strategy for prevention of pneumococcal disease will likely include WCV and PPVs. However these vaccines will impact disease pathogenesis in a different manner than PCVs. Prevention of pneumococcal NP colonization should not be expected, nor is it desirable because risks for NP colonization by other replacement organisms into the ecological niche vacated by all pneumococci may have consequences. The expression biology of capsule and surface protein antigens are phase dependent. Therefore, the immune response will be different and the mechanism of protection divergent. WCVs and PPVs may be alternative strategies in low income developing countries to protect against invasive disease and reduce NP carriage load.

Redistribution of Streptococcus pneumoniae Serotypes After Nationwide 13-valent Pneumococcal Conjugate Vaccine Program in Children in Northern Taiwan

BACKGROUND

After the introduction of 13-valent pneumococcal conjugate vaccine (PCV13) against Streptococcus pneumoniae, public health officials in Taiwan monitored a decline in circulating vaccine serotypes and the emergence of nonvaccine serotypes in children with invasive pneumococcal disease. A gradually expanded PCV13 national immunization program was launched in 2013 in Taiwan. Here, we evaluate the changes in the distribution of pneumococcal serotypes and antimicrobial nonsusceptibility in children during the evolution of vaccination policy.

METHODS

S. pneumoniae isolates from children with pneumococcal disease were collected and serotyped from 2010 to 2015 in northern Taiwan. PCVs were administered at the recipients' expense between 2010 and 2012, and then PCV13 was partially reimbursed by the government beginning in 2013. The distribution and diversity of serotypes were analyzed along with their antimicrobial susceptibilities.

RESULTS

Among a total of 498 isolates, the proportion of invasive pneumococcal disease isolates declined (47.1%-10.6%) during the study period, and serotype diversity increased after 2011. Between 2010 and 2012, the dominant serotypes were 19A, 19F, 3, 6B and 14, and serotype 19A rose from 44.1% to 57.5%. Serotypes 19A, 15A, 19F and 15B were more prevalent from 2013 to 2015, and serotype 19A decreased from 42.1% to 4.5%. Serotypes 19F and 15A became the most commonly detected serotypes in 2015. Overall, PCV13 additional serotypes were reduced by 80% (P < 0.0001) but nonvaccine serotypes increased from 8.8% to 51.5% (P < 0.0001).

CONCLUSIONS

The step-by-step PCV13 national immunization program is effective against pneumococcal disease in Taiwanese children, mainly by reducing PCV13 additional serotypes.

Nasopharyngeal s. pneumoniae carriage and density in Belgian infants after 9 years of pneumococcal conjugate vaccine programme

BACKGROUND

In Belgium, the infant pneumococcal conjugate vaccine (PCV) programme changed from PCV7 (2007-2011) to PCV13 (2011-2015) and to PCV10 (2015-2016). A 3-year nasopharyngeal carriage study was initiated during the programme switch in 2016. Main objective of the year 1 assessment was to obtain a baseline measurement of pneumococcal carriage prevalence, carriage density, serotype distribution and antibiotic resistance.

MATERIALS/METHODS

Two infant populations aged 6-30 months and without use of antibiotics in the seven days prior to sampling were approached: (1) attending one of 85 randomly selected day-care centres (DCC); (2) presenting with AOM at study-trained general practitioners and paediatricians. Demographic and clinical characteristics were documented and a single nasopharyngeal swab was taken. S. pneumoniae were cultured, screened for antibiotic resistance and serotyped, and quantitative Taqman real-time PCR (qRT-PCR) targeting LytA was performed.

RESULTS

Culture-based (DCC: 462/760; 60.8% - AOM: 27/39; 69.2%) and LytA-based (DCC: 603/753; 80.1% - AOM: 32/39; 82.1%) carriage prevalence was high. Average pneumococcal DNA load in LytA-positive day-care samples was 6.5 × 10⁶ copies/µl (95%CI = 3.9-9.2 × 10⁶, median = 3.5 × 10⁵); DNA load was positively associated with signs of common cold and negatively with previous antibiotic use. Culture-based frequency of 13 pneumococcal vaccine (PCV) serotypes was 5.4% in DCC and 7.7% in AOM, with 19F and 14 being most frequent, and frequencies below 0.5% for serotypes 3, 6A, 19A in both populations. Predominant non-PCV serotypes were 23B and 23A in day-care and 11A in infants with AOM. In day-care, resistance to penicillin was rare (<0.5%) and absent against levofloxacin; 32.7% and 16.9% isolates were cotrimoxazole- and erythromycin-resistant respectively.

CONCLUSION

Four years after PCV13 introduction in the vaccination programme, PCV13 serotype carriage was rare in infants throughout Belgium and penicillin resistance was rare. Continued surveillance in the context of a PCV programme switch is necessary.

The rise and fall of pneumococcal serotypes carried in the PCV era

Streptococcus pneumoniae is a major cause of meningitis, sepsis and pneumonia worldwide. Vaccination using pneumococcal conjugate vaccines (PCV) has therefore been part of the UK's childhood immunisation programme since 2006. Here we describe pneumococcal carriage rates in children under five years of age attending the paediatric department of a large UK hospital in response to vaccine implementation over seven winter seasons from 2006 to 2013. S. pneumoniae (n=696) were isolated from nasopharyngeal swabs (n=2267) collected during seven consecutive winters, October to March, 2006/7 to 2012/13. This includes the period immediately following the introduction of the seven-valent pneumococcal conjugate vaccine (PCV7) in 2006 in addition to pre- and post-PCV13 introduction in 2010. We show a decrease in PCV13 vaccine serotypes (VT) in the three years following PCV13 vaccine implementation (2010/11 to 2012/13). Serotype 6A represented the only observed VT following PCV13 implementation with all others (including PCV7 serotypes) absent from carriage. Overall pneumococcal carriage, attributable to non-VT (NVT), was consistent across all sampling years with a mean of 31·1%. The ten most frequently isolated NVTs were 6C, 11A, 15B, 23B, 15A, 21, 22F, 35F, 23A and 15C. Fluctuations in the prevalence of each were however noted. Comparing prevalence at 2006/07 with 2012/13 only 15A was shown to have increased significantly (p value of 0·003) during the course of PCV implementation. These data support the increasing evidence that the primary effect of PCVs is due to population immunity by reducing or eliminating the carriage of invasive VT serotypes. With IPD being increasingly attributed to non-vaccine serotypes, surveillance of carriage data continues to act as an early warning system for vaccine design and public health policy that require continual data of both carried pneumococcal serotypes and IPD attributed serotype data.

Whole-genome Sequencing for Surveillance of Invasive Pneumococcal Diseases in Ontario, Canada: Rapid Prediction of Genotype, Antibiotic Resistance and Characterization of Emerging Serotype 22F

Background: Molecular typing is essential for inferring genetic relatedness between bacterial pathogens. In this study, we applied whole genome sequencing (WGS) for rapid prediction of sequence type and antibiotic resistance for invasive pneumococcal isolates. Methods: 240 isolates from adults (≥50 years old) in Ontario, Canada during 2009 to 2013 were subjected to WGS. Sequence type, antibiotic susceptibility and resistance were predicted directly from short reads. Emerging non-vaccine serotype 22F was further characterized by WGS. Results: Sequence type was successfully determined for 98.3% of isolates. The overall sensitivity and specificity for antibiotic resistance prediction were 95 and 100% respectively, compared to standard susceptibility testing methods. WGS-based phylogeny divided emerging 22F (ST433) strains into two distinct clades: clade A harboring a 23 kb-prophage and anti-phage PhD/Doc system and clade B with virulence-related proteases. Five isolates in clade A developed macrolide resistance via 5.1 kb mega element recombination (encoding mefE and msrD), while one isolate in clade B displayed quinolone resistance via a gyrA mutation. Conclusions: WGS is valuable for routine surveillance of pneumococcal clinical isolates and facilitates prediction of genotype and antibiotic resistance. The emergence of 22F in Ontario in the post-vaccine era and evidence of evolution and divergence of the 22F population warrants heightened pneumococcal molecular surveillance.

The incidence of invasive pneumococcal serotype 3 disease in the Danish population is not reduced by PCV-13 vaccination

Since 2010, Denmark has included the 13-valent pneumococcal conjugated vaccine (PCV-13) in the childhood immunization programme. However, serotype 3 remains as an important cause of invasive pneumococcal disease (IPD) in Denmark. IPD surveillance data (1999-2016) was used to calculate the incidence and age-distribution of serotype 3 IPD, and the effect of PCV-13 on serotype 3 IPD incidence was examined. The incidence of serotype 3 IPD in the age group below 65 years was 0.51/100,000 pre PCV-13, and 0.45/100,000 post PCV-13. In the group 0-4 years, serotype 3 IPD incidence was 0.28/100,000 pre PCV-13, and 0.16/100,000 post PCV-13. Serotype 3 IPD incidence in the elderly showed a mean of 4.27/100,000 pre PCV-13, and 4.32/100,000 post PCV-13. PCV-13 childhood immunization in Denmark has not lead to a reduction of the incidence of IPD caused by serotype 3. The reason behind this missing effect needs to be investigated further.

In vitro and in vivo comparison of transport media for detecting nasopharyngeal carriage of Streptococcus pneumoniae

Background

As a standard method for pneumococcal carriage studies, the World Health Organization recommends nasopharyngeal swabs be transported and stored at cool temperatures in a medium containing skim-milk, tryptone, glucose and glycerol (STGG). An enrichment broth used for transport at room temperature in three carriage studies performed in Norway may have a higher sensitivity than STGG. We therefore compared the media in vitro and in vivo.

Methods

For the in vitro component, three strains (serotype 4, 19F and 3) were suspended in STGG and enrichment broth. Recovery was compared using latex agglutination, quantification of bacterial loads by real-time PCR of the lytA gene, and counting colonies from incubated plates. For the in vivo comparison, paired swabs were obtained from 100 children and transported in STGG at cool temperatures or in enrichment broth at room temperature. Carriage was identified by latex agglutination and confirmed by Quellung reaction.

Results

In vitro, the cycle threshold values obtained by PCR did not differ between the two media (p = 0.853) and no clear difference in colony counts was apparent after incubation (p = 0.593). In vivo, pneumococci were recovered in 46% of swabs transported in STGG and 51% of those transported in enrichment broth (Kappa statistic 0.90, p = 0.063).

Discussion

Overall, no statistical differences in sensitivity were found between STGG and enrichment broth. Nevertheless, some serotype differences were observed and STGG appeared slightly less sensitive than enrichment broth for detection of nasopharyngeal carriage of pneumococci by culturing. We recommend the continued use of STGG for transport and storage of nasopharyngeal swabs in pneumococcal carriage studies for the benefit of comparability between studies and settings, including more resource-limited settings.

Other age groups than children need to be considered as carriers of Streptococcal pneumoniae serotypes

We need to raise the issue that focus on children as the only carriage group for pneumococci is not optimal; we need to consider that other age groups might also be carriers of pneumococcal serotypes causing invasive pneumococcal diseases (IPD) in unvaccinated age groups. The pneumococcal conjugate vaccines (PCV) have successfully removed IPD from vaccinated children. Studies have shown an effect of PCV reducing the pneumococcal carriage of PCV serotypes in children. The status for several countries having used PCV for many years is that they do not see PCV serotypes neither carried nor as a cause of IPD in children. PCV vaccination of children has shown a herd protection effect in unvaccinated groups as a reduction in IPD cases caused by PCV serotypes. However, not all PCV serotypes have disappeared as the cause of IPD in the unvaccinated age groups. The author therefore believes that if we are to see PCV serotypes disappear as a cause of IPD in unvaccinated age groups, we need to perform further carriage studies to examine carriage in other age groups. Alternatively, all age groups should be vaccinated against pneumococci to eliminate IPD caused by PCV serotypes from possible hidden carriers.

Impact of the 13-valent pneumococcal conjugate vaccine on Streptococcus pneumoniae multiple serotype carriage

INTRODUCTION

Pneumococcal multiple serotype carriage is important for evolution of the species and to understand how the pneumococcal population is changing with vaccination. We aimed to determine the impact of the 13-valent pneumococcal conjugate vaccine (PCV13) on multiple serotype carriage.

METHODS AND MATERIALS

Nasopharyngeal samples from fully vaccinated pneumococcal carriers (4 doses of PCV13, n=141, aged 18-72months) or from non-vaccinated pneumococcal carriers (0 doses of any PCV, n=140, same age group) were analyzed. Multiple serotype carriage was evaluated by DNA hybridization with a molecular serotyping microarray that detects all known serotypes.

RESULTS

Vaccinated children had a lower prevalence of multiple serotype carriage than the non-vaccinated group (20.6% vs 29.3%, p=0.097), and a significantly lower proportion of PCV13 serotypes (6.4% vs 38.5%, p=0.0001). PCV13 serotypes found among vaccinated children were mostly detected as a minor serotype in co-colonization with a more abundant non-vaccine serotype. Vaccinated children were colonized by a significantly higher proportion of commensal non-pneumococcal Streptococcus spp. (58.2% vs 42.8%, p=0.012). In vaccinated children there were significantly less non-vaccine type (NVT) co-colonization events than expected based on the distribution of these serotypes in non-vaccinated children.

CONCLUSIONS

The results suggest that vaccinated children have lower pneumococcal multiple serotype carriage prevalence due to higher competitive abilities of non-vaccine serotypes expanding after PCV13 use. This might represent an additional benefit of PCV13, as decreased co-colonization rates translate into decreased opportunities for horizontal gene transfer and might have implications for the evolution and virulence of pneumococci.

Pneumococcal serotype evolution in Western Europe

BACKGROUND

Pneumococcal diseases remain a leading cause of vaccine-preventable death worldwide in children <5 years of age. The seven-valent pneumococcal conjugate vaccine (PCV7) was approved in 2001 in Europe and was introduced into the national immunization programmes of many European countries from 2006-2008. In 2009, higher-valent PCVs (PCV10 and PCV13) became available, replacing PCV7 from 2009-2011. This article describes the evolution of vaccine and non-vaccine serotypes causing invasive pneumococcal disease (IPD) following the introduction of PCVs in Western Europe, based on data from publicly-available medical publications and national surveillance systems from January 2010 to May 2015.

DISCUSSION

In countries with high vaccine uptake, 5-7 years after PCV7 introduction IPD caused by vaccine serotypes has almost disappeared in children. Non-PCV7 serotypes have emerged, particularly serotypes 19A, 7 F, 3 and 1. A rapid and significant reduction of the additional serotypes included in higher-valent vaccines has been observed consistently following the introduction of these vaccines. A significant and rapid decline of serotypes 19A, 7 F, 1 and 6A in both vaccine-eligible and older age groups has been observed in countries using PCV13 while serotype 19A and 3 has increased in countries using PCV10. Serotype 3 has become one of the most prevalent serotypes in adults, with some reduction only in the UK and France. Serotype diversity increased and varied by age group, the type of vaccine in use, and the time since the introduction of higher-valent PCVs. Serotypes that are currently more frequent include 24 F, 22 F, 8 and 15A in countries that use PCV13, and serotypes 19A and 3 in countries that use PCV10. Compared with the time before the introduction of higher valent PCVs, to date, there is no single '19A-like' serotype emerging across countries and most of the newly emerging non-PCV13 vaccine types are less invasive with a low case-carrier ratio.

CONCLUSIONS

It is important to closely monitor not only evolving serotypes but also the magnitude of the effect in order to evaluate the overall impact of pneumococcal vaccination programmes and to initiate the appropriate vaccination strategy. Emerging serotypes may also need to be considered for the future development of new vaccines.