Carriage of Streptococcus pneumoniae in healthy Norwegian children attending day-care centres

Multicenter study of pneumococcal carriage in children 2 to 4 years of age in the winter seasons of 2017-2019 in Irbid and Madaba governorates of Jordan

Streptococcus pneumoniae is one of the leading causes of death worldwide. It disseminates through colonizers and causes serious infections. Aims of this study are to determine pneumococcal carriage rate, resistance, serotype distribution, and coverage of pneumococcal conjugate vaccines from children attending day care centers from Irbid and Madaba in Jordan. Nasopharyngeal swabs were collected from day care centers (DCCs) of healthy Jordanian children 2–4 years of age from four regions of Madaba (n = 596), and from eastern Irbid (n = 423). Swabs were cultivated on Columbia blood agar base supplemented with 5% sheep blood and incubated for 18–24 hours at 37°C with 5% CO₂. Alpha-hemolytic isolates were tested for optochin sensitivity and bile solubility for identification. Isolates were analyzed for antimicrobial susceptibility by the Vitek2 system and E-test (BioMérieux). Serotyping was performed using the Neufeld Quellung method. A total of 341 pneumococcal strains were isolated from 1019 nasopharyngeal (NP) samples of healthy children attending DCCs for two winter seasons from 2017–2019. Carriage rate in eastern Irbid for both seasons was 29.6% and for Madaba 37.9%. Resistance rates for Irbid and Madaba, respectively, were as follows: Penicillin (86.3%; 94.4%), erythromycin (57.0%; 78.2%), clindamycin (30.8%; 47.2%), trimethoprim-sulfamethoxazole (68.6%; 86.6%), and tetracycline (45.7%; 51.9%). Predominant serotypes for Irbid were 19F (20.8%), 23F (12.0%), 6A (10.4%), and 6B (9.6%); whereas for Madaba were 19F (24.5%), 14 (7.4%), 6A (6.9%) and 23F (6.5%). Serotype coverage of the thirteen valent pneumococcal conjugate vaccine (PCV13) was about 65% for both regions. Over 96% of isolates with PCV13 serotypes in this study were resistant to penicillin with the exception of serotypes 3 and 5. As a conclusion resistance and carriage rates among the age group 2 to 4 years reached an alarming rate especially among vaccine types, which can be controlled by pneumococcal conjugate vaccination strategies.

The serotype distribution among healthy carriers before vaccination is essential for predicting the impact of pneumococcal conjugate vaccine on invasive disease

Pneumococcal conjugate vaccines (PCVs) have substantially reduced morbidity and mortality of pneumococcal disease. The impact of the 7-valent PCV on all-serotype invasive pneumococcal disease (IPD) among children was reported to vary between high-income countries. We investigate the ability to predict this heterogeneity from pre-vaccination data. We propose a parsimonious model that predicts the impact of PCVs from the odds of vaccine serotype (VT) among carriers and IPD cases in the pre-PCV period, assuming that VT are eliminated in a mature PCV programme, that full serotype replacement occurs in carriage and that invasiveness of the NVT group is unchanged. We test model performance against the reported impact of PCV7 on childhood IPD in high-income countries from a recent meta-analysis. The odds of pre-PCV7 VT IPD, PCV schedule, PCV coverage and whether a catch up campaign was used for introduction was gathered from the same analysis. We conducted a literature review and meta-analysis to obtain the odds of pre-PCV7 VT carriage in the respective settings. The model predicted the reported impact on childhood IPD of mature PCV programmes; the ratio of predicted and observed incidence risk ratios was close to 1 in all settings. In the high income settings studied differences in schedule, coverage, and catch up campaigns were not associated with the observed heterogeneity in impact of PCV7 on childhood all-serotype IPD. The pre-PCV7 proportion of VT IPD alone also had limited predictive value. The pre-PCV7 proportion of VT carriage and IPD are the main determinants for the impact of PCV7 on childhood IPD and can be combined in a simple model to provide predictions of the vaccine preventable burden of IPD.

Pneumococcal vaccines (PCVs) that protect children against 7, 10 and 13 of the most pathogenic pneumococcal serotypes have substantially reduced childhood morbidity and mortality. A recent analysis that evaluated the impact of the 7 valent PCV in multiple high income settings in North America, Europe and Oceania found that the magnitude of all-serotype invasive pneumococcal disease reduction varied greatly between settings (24%-83%). We explored potential sources for that variation, including differences in disease epidemiology before vaccination, vaccine coverage, vaccine schedules and the use of catch-up campaigns for introduction. We find that differences in reported disease impact among mature PCV programmes are likely to be unrelated to the differences in the vaccine programme but can be predicted from a simple model based on pre-vaccination epidemiology, in particular the proportion of vaccine serotypes detected among patients with invasive pneumococcal disease and the proportion of vaccine serotypes that are found in the nasopharynx of healthy individuals. This model presents a useful tool to estimate the potential impact of PCVs (as a relative rate reduction), highlights the essential role of pre-vaccination carriage in healthy individuals for disease impact of PCVs and can estimate the prevented burden of disease where disease surveillance is unavailable.

Low rate of pneumococci non-susceptible to penicillin in healthy Swedish toddlers

BACKGROUND

Infection caused by Streptococcus pneumoniae is the leading cause of mortality in children worldwide. The aim of this study was to determine if a noted increase in non-susceptibility to penicillin among pneumococcal clinical isolates from young children reflected a similar increase in healthy children.

METHODS

During 2004-2005, before the conjugate pneumococcal vaccine was introduced in Sweden, 663 healthy children (13-24 months of age) attending 17 child health centres in Gothenburg, Sweden, were cultured for bacteria in the nasopharynx. Social factors were identified through a parental questionnaire. Pneumococcal serotypes and antibiotic resistance rates were determined. Antibiotic resistance was also monitored in 162 simultaneously obtained nasopharyngeal pneumococci isolated from clinical samples.

RESULTS

The healthy children frequently carried pneumococci (45%), Moraxella catarrhalis (54%), and Haemophilus influenzae (22%). The carriage rates for all these pathogens were higher in children attending day care centres compared to children staying at home (p < 0.001). The dominating pneumococcal serotypes were 6B, 19F, 23F, and 6A. Non-susceptibility to penicillin was low (4.0%) and only exceeded by that to trimethoprim-sulfamethoxazole (9.8%). Both rates were higher in the clinical isolates (9.3% and 16.7%, respectively; p < 0.05). No relationships to geographic area, day care attendance, recent antibiotic use, or travel abroad were shown for any specific serotype or for the presence of penicillin-non-susceptible pneumococci in the healthy children.

CONCLUSIONS

Pneumococcal resistance rates in the healthy child population were low and did not reflect the higher rates noted at the laboratory in clinical samples obtained before and during the study.

Community-acquired pneumonia (CAP) in children in Oslo, Norway

AIM

To investigate the epidemiology and clinical characteristics of community acquired pneumonia (CAP) in children before the introduction of the 7-valent pneumococcal vaccine in the national vaccination programme.

METHODS

For the period 21 May 2003 to 20 May 2005 hospitalization rates for pneumonia in children were obtained from retrospective studies of medical journals. Pneumonia was also studied prospectively in children less than sixteen years old referred to Ullevål University Hospital (Oslo) in the same time period.

RESULTS

The overall observed hospitalization rate of pneumonia was 14.7/10 000 (95% CI: 12.2-17.1), for children under five it was 32.8/10 000 (95% CI: 26.8-38.8), and for children under two 42.1/10 000 (95% CI: 32.0-52.3). In the clinical study 123 children, of whom 59% (73) were boys, met the inclusion criteria and were enrolled. Only 2.4% (3) had pneumonia complicated with pleural effusion and in general few complications were observed. No patients required assisted ventilation, and none were transferred to the intensive care unit. Penicillin was effective as treatment for pneumonia.

CONCLUSION

Pneumonia, seen in a paediatric department in Oslo, is a common but benign disease. Penicillin is effective as treatment for pneumonia in Norwegian children.

Phenotypic and genotypic characterization of Streptococcus pneumoniae strains colonizing children attending day-care centers in Norway

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 England(14)-9 clone, and 19 isolates (3.7%) belonged to, or were single-locus variants of, the Portugal(19F)-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.

A second pilus type in Streptococcus pneumoniae is prevalent in emerging serotypes and mediates adhesion to host cells

Analysis of publicly available genomes of Streptococcus pneumoniae has led to the identification of a new genomic element containing genes typical of gram-positive pilus islets (PIs). Here, we demonstrate that this genomic region, herein referred to as PI-2 (consisting of pitA, sipA, pitB, srtG1, and srtG2) codes for a second functional pilus in pneumococcus. Polymerization of the PI-2 pilus requires the backbone protein PitB as well as the sortase SrtG1 and the signal peptidase-like protein SipA. Presence of PI-2 correlates with the genotype as defined by multilocus sequence typing and clonal complex (CC). The PI-2-positive CCs are associated with serotypes 1, 2, 7F, 19A, and 19F, considered to be emerging serotypes in both industrialized and developing countries. Interestingly, strains belonging to CC271 (where sequence type 271 is the predicted founder of the CC) contain both PI-1 and PI-2, as revealed by genome analyses. In these strains both pili are surface exposed and independently assembled. Furthermore, in vitro experiments provide evidence that the pilus encoded by PI-2 of S. pneumoniae is involved in adherence. Thus, pneumococci encode at least two types of pili that play a role in the initial host cell contact to the respiratory tract and are potential antigens for inclusion in a new generation of pneumococcal vaccines.