Haemophilus influenzae carriage and antibiotic resistance profile in Belgian infants over a three-year period (2016-2018).

Background: Non-typeable Haemophilus influenzae has become increasingly important as a causative agent of invasive diseases following vaccination against H. influenzae type b. The emergence of antibiotic resistance underscores the necessity to investigate typeable non-b carriage and non-typeable H. influenzae (NTHi) in children. Methods: Nasopharyngeal swab samples were taken over a three-year period (2016-2018) from 336 children (6-30 months of age) attending daycare centers (DCCs) in Belgium, and from 218 children with acute otitis media (AOM). Biotype, serotype, and antibiotic resistance of H. influenzae strains were determined phenotypically. Mutations in the ftsI gene were explored in 129 strains that were resistant or had reduced susceptibility to beta-lactam antibiotics. Results were compared with data obtained during overlapping time periods from 94 children experiencing invasive disease. Results: Overall, NTHi was most frequently present in both carriage (DCC, AOM) and invasive group. This was followed by serotype "f" (2.2%) and "e" (1.4%) in carriage, and "b" (16.0%), "f" (11.7%), and "a" (4.3%) in invasive strains. Biotype II was most prevalent in all studied groups, followed by biotype III in carriage and I in invasive strains. Strains from both groups showed highest resistance to ampicillin (26.7% in carriage vs. 18.1% in invasive group). A higher frequency of ftsI mutations were found in the AOM group than the DCC group (21.6 vs. 14.9% - p = 0.056). Even more so, the proportion of biotype III strains that carried a ftsI mutation was higher in AOM compared to DCC (50.0 vs. 26.3% - p < 0.01) and invasive group. Conclusion: In both groups, NTHi was most frequently circulating, while specific encapsulated serotypes for carriage and invasive group were found. Biotypes I, II and III were more frequently present in the carriage and invasive group. The carriage group had a higher resistance-frequency to the analyzed antibiotics than the invasive group. Interestingly, a higher degree of ftsI mutations was found in children with AOM compared to DCC and invasive group. This data helps understanding the H. influenzae carriage in Belgian children, as such information is scarce.

Serotype 19A and 6C Account for One-Third of Pneumococcal Carriage Among Belgian Day-Care Children Four Years After a Shift to a Lower-Valent PCV.

BACKGROUND: Pneumococcal conjugate vaccines (PCVs) effectively reduce infection and asymptomatic carriage of Streptococcus pneumoniae vaccine serotypes. In 2016, Belgium replaced its infant PCV13 program by a 4-year period of PCV10. Concomitantly, S. pneumoniae serotype carriage was monitored together with the carriage of other nasopharyngeal pathogens in children attending day-care centers. METHODS: From 2016 to 2019, a total of 3459 nasopharyngeal swabs were obtained from children aged 6-30 months. Culture and qPCR were used for the identification of S. pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Staphylococcus aureus and for serotyping and antimicrobial susceptibility assessment of S. pneumoniae strains. RESULTS: S. pneumoniae colonization was frequent and stable over the study years. H. influenzae and M. catarrhalis were more frequently carried (P < .001) than S. pneumoniae, by, respectively, 92.3% and 91.0% of children. Prevalence of all PCV13 serotypes together increased significantly over time from 5.8% to 19.6% (P < .001) and was attributable to the increasing prevalence of serotype 19A. Coincidently, non-vaccine serotype 6C increased (P < .001) and the overall pneumococcal non-susceptibility to tetracycline and erythromycin. Non-susceptibility to cotrimoxazole decreased (P < .001). CONCLUSIONS: The switch to a PCV program no longer covering serotypes 19A, 6A, and 3 was associated with a sustained increase of serotypes 19A and 6C in healthy children, similarly as in invasive pneumococcal disease. This resulted in a re-introduction of the 13-valent conjugate vaccine during the summer of 2019.

Change in COVID19 outbreak pattern following vaccination in long-term care facilities in Flanders, Belgium.

INTRODUCTION: Long term care facilities for elderly (LTCFs) in Europe encountered a high disease burden at the start of the COVID-19 pandemic. Therefore, these facilities were the first to receive COVID-19 vaccines in many European countries. A limited COVID-19 vaccine supply early 2021 resulted in a majority of residents and healthcare workers (HCWs) in LTCFs being vaccinated compared to a minority in the general population. This study exploits this imbalance to assess the efficiency of COVID-19 vaccination in containing outbreaks in LTCFs. METHODS: Exploratory statistics were performed using data from a COVID-19 surveillance system covering all 842 LTCFs in Flanders (the northern region of Belgium). The number and size of COVID-19 outbreaks in LTCFs were compared (1) before and after introducing vaccines and (2) with the status of the pandemic in the general population. Based on individual data from 15 LTCFs, the infection rate and symptoms of vaccinated and unvaccinated residents and HCWs were compared during a COVID-19 outbreak. RESULTS: 95.8% of the residents and 90.9% of the HCWs in Flemish LTCFs were vaccinated before May 30, 2021. Before vaccine introduction, residents in LTCFs were 10 times more likely to test positive for COVID-19 than the general population of Flanders. This ratio reversed after vaccination. Furthermore, after vaccination fewer and shorter outbreaks were observed involving fewer residents. During these outbreaks, vaccinated and unvaccinated residents were equally likely to test positive, but positive vaccinated residents were less likely to develop severe symptoms. In contrast, unvaccinated HCWs were more likely to test positive. CONCLUSION: In the first half of 2021, two-dose vaccination was highly efficient in preventing and containing outbreaks in LTCFs, reducing COVID-19 hospitalizations and deaths. The high likelihood of unvaccinated HCWs to be involved in COVID-19 outbreaks in vaccinated LTCFs emphasizes the importance of vaccinating HCWs.

Characterization of Emerging Serotype 19A Pneumococcal Strains in Invasive Disease and Carriage, Belgium.

After switching from 13-valent to 10-valent pneumococcal conjugate vaccine (PCV10) (2015-2016) for children in Belgium, we observed rapid reemergence of serotype 19A invasive pneumococcal disease (IPD). Whole-genome sequencing of 166 serotype 19A IPD isolates from children (n = 54) and older adults (n = 56) and carriage isolates from healthy children (n = 56) collected after the vaccine switch (2017-2018) showed 24 sequence types (STs). ST416 (global pneumococcal sequence cluster [GPSC] 4) and ST994 (GPSC146) accounted for 75.9% of IPD strains from children and 65.7% of IPD (children and older adults) and carriage isolates in the PCV10 period (2017-2018). These STs differed from predominant 19A IPD STs after introduction of PCV7 (2011) in Belgium (ST193 [GPSC11] and ST276 [GPSC10]), which indicates that prediction of emerging strains cannot be based solely on historical emerging strains. Despite their susceptible antimicrobial drug profiles, these clones spread in carriage and IPD during PCV10 use.

Detection of SARS-CoV-2 in young children attending day-care centres in Belgium, May 2020 to February 2022.

Presence of SARS-CoV-2 was monitored in nasopharyngeal samples from young children aged 6-30 months attending day-care centres (DCCs) in Belgium from May 2020-February 2022. SARS-CoV-2 carriage among DCC children was only detected from November 2021, after emergence of Delta and Omicron variants, in 9 of the 42 DCCs screened. In only one DCC, two children tested positive for SARS-CoV-2 at the same sampling time point, suggesting limited transmission of SARS-CoV-2 in Belgian DCCs among young children during the studied period.

Identifying immunity gaps for measles using Belgian serial serology data.

Vaccine-preventable diseases, such as measles, have been re-emerging in countries with moderate to high vaccine uptake. It is increasingly important to identify and close immunity gaps and increase coverage of routine childhood vaccinations, including two doses of the measles-mumps-rubella vaccine (MMR). Here, we present a simple cohort model relying on a Bayesian approach to evaluate the evolution of measles seroprevalence in Belgium using the three most recent cross-sectional serological survey data collections (2002, 2006 and 2013) and information regarding vaccine properties. We find measles seroprevalence profiles to be similar for the different regions in Belgium. These profiles exhibit a drop in seroprevalence in birth cohorts that were offered vaccination at suboptimal coverages in the first years after routine vaccination has been started up. This immunity gap is observed across all cross-sectional survey years, although it is more pronounced in survey year 2013. At present, the COVID-19 pandemic could negatively impact the immunization coverage worldwide, thereby increasing the need for additional immunization programs in groups of children that are impacted by this. Therefore, it is now even more important to identify existing immunity gaps and to sustain and reach vaccine-derived measles immunity goals.

Seroprevalence of IgG antibodies against SARS-CoV-2 - a serial prospective cross-sectional nationwide study of residual samples, Belgium, March to October 2020.

BackgroundTo control epidemic waves, it is important to know the susceptibility to SARS-CoV-2 and its evolution over time in relation to the control measures taken.AimTo assess the evolving SARS-CoV-2 seroprevalence and seroincidence related to the first national lockdown in Belgium, we performed a nationwide seroprevalence study, stratified by age, sex and region using 3,000-4,000 residual samples during seven periods between 30 March and 17 October 2020.MethodsWe analysed residual sera from ambulatory patients for IgG antibodies against the SARS-CoV-2 S1 protein with a semiquantitative commercial ELISA. Weighted seroprevalence (overall and by age category and sex) and seroincidence during seven consecutive periods were estimated for the Belgian population while accommodating test-specific sensitivity and specificity.ResultsThe weighted overall seroprevalence initially increased from 1.8% (95% credible interval (CrI): 1.0-2.6) to 5.3% (95% CrI: 4.2-6.4), implying a seroincidence of 3.4% (95% CrI: 2.4-4.6) between the first and second collection period over a period of 3 weeks during lockdown (start lockdown mid-March 2020). Thereafter, seroprevalence stabilised, however, significant decreases were observed when comparing the third with the fifth, sixth and seventh period, resulting in negative seroincidence estimates after lockdown was lifted. We estimated for the last collection period mid-October 2020 a weighted overall seroprevalence of 4.2% (95% CrI: 3.1-5.2).ConclusionDuring lockdown, an initially small but increasing fraction of the Belgian population showed serologically detectable signs of exposure to SARS-CoV-2, which did not further increase when confinement measures eased and full lockdown was lifted.

COVID-19 mortality, excess mortality, deaths per million and infection fatality ratio, Belgium, 9 March 2020 to 28 June 2020.

BackgroundCOVID-19 mortality, excess mortality, deaths per million population (DPM), infection fatality ratio (IFR) and case fatality ratio (CFR) are reported and compared for many countries globally. These measures may appear objective, however, they should be interpreted with caution.AimWe examined reported COVID-19-related mortality in Belgium from 9 March 2020 to 28 June 2020, placing it against the background of excess mortality and compared the DPM and IFR between countries and within subgroups.MethodsThe relation between COVID-19-related mortality and excess mortality was evaluated by comparing COVID-19 mortality and the difference between observed and weekly average predictions of all-cause mortality. DPM were evaluated using demographic data of the Belgian population. The number of infections was estimated by a stochastic compartmental model. The IFR was estimated using a delay distribution between infection and death.ResultsIn the study period, 9,621 COVID-19-related deaths were reported, which is close to the excess mortality estimated using weekly averages (8,985 deaths). This translates to 837 DPM and an IFR of 1.5% in the general population. Both DPM and IFR increase with age and are substantially larger in the nursing home population.DiscussionDuring the first pandemic wave, Belgium had no discrepancy between COVID-19-related mortality and excess mortality. In light of this close agreement, it is useful to consider the DPM and IFR, which are both age, sex, and nursing home population-dependent. Comparison of COVID-19 mortality between countries should rather be based on excess mortality than on COVID-19-related mortality.

Streptococcus pneumoniae Serotypes Carried by Young Children and Their Association With Acute Otitis Media During the Period 2016-2019.

Background: Streptococcus pneumoniae (Sp) is a major cause of acute otitis media (AOM). Pneumococcal conjugate vaccine (PCV) programs have altered pneumococcal serotype epidemiology in disease and carriage. In this study, we used samples collected during a cross-sectional study to examine if the clinical picture of acute otitis media (AOM) in young children exposed to the PCV program in Belgium was related to the carried pneumococcal strains, and if their carriage profile differed from healthy children attending daycare centers. Material/Methods: In three collection periods from February 2016 to May 2018, nasopharyngeal swabs and background characteristics were collected from children aged 6-30 months either presenting at their physician with AOM (AOM-group) or healthy and attending day care (DCC-group). Clinical signs of AOM episodes and treatment schedule were registered by the physicians. Sp was detected, quantified, and characterized using both conventional culture analysis and real-time PCR analysis. Results: Among 3,264 collected samples, overall pneumococcal carriage and density were found at similar rates in both AOM and DCC. As expected non-vaccine serotypes were most frequent: 23B (AOM: 12.3%; DCC: 17.4%), 11A (AOM: 7.5%; DCC: 7.4%) and 15B (AOM: 7.5%; DCC: 7.1%). Serotypes 3, 6C, 7B, 9N, 12F, 17F, and 29 were more often found in AOM than in DCC (p-value < 0.05), whereas 23A and 23B were less often present in AOM (p-value < 0.05). Antibiotic non-susceptibility of Sp strains was similar in both groups. No predictors of AOM severity were identified. Conclusion: In the present study, overall carriage prevalence and density of S. pneumoniae were found similar in young children with AOM and in healthy children attending day-care centers in Belgium. Certain serotypes not currently included in the PCV vaccines were found to be carried more often in children with AOM than in DCC, a finding that might suggest a relationship between these serotypes and AOM.

Case-Control Microbiome Study of Chronic Otitis Media with Effusion in Children Points at Streptococcus salivarius as a Pathobiont-Inhibiting Species.

Chronic otitis media with effusion (OME) has been associated with a shift in microbiome composition and microbial interaction in the upper respiratory tract (URT). While most studies have focused on potential pathogens, this study aimed to find bacteria that could be protective against OME through a case-control microbiome study and characterization of isolates from healthy subjects. The URT and ear microbiome profiles of 70 chronic OME patients and 53 controls were compared by 16S rRNA amplicon sequencing. Haemophilus influenzae was the most frequent classic middle ear pathobiont. However, other taxa, especially Alloiococcus otitis, were also frequently detected in the ear canal of OME patients. Streptococci of the salivarius group and Acinetobacter lwoffii were more abundant in the nasopharynx of healthy controls than in OME patients. In addition to the microbiome analysis, 142 taxa were isolated from healthy individuals, and 79 isolates of 13 different Streptococcus species were tested for their pathobiont-inhibiting potential. Of these, Streptococcus salivarius isolates showed a superior capacity to inhibit the growth of H. influenzae, Moraxella catarrhalis, Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, A. otitis, and Corynebacterium otitidis S. salivarius strains thus show potential as a probiotic for prevention or treatment of OME based on their overrepresentation in the healthy nasopharynx and their ability to inhibit the growth of respiratory pathobionts. (This study has been registered at ClinicalTrials.gov under registration no. NCT03109496.)IMPORTANCE The majority of probiotics marketed today target gastrointestinal health. This study searched for bacteria native to the human upper respiratory tract, with a beneficial potential for respiratory and middle ear health. Comparison of the microbiomes of children with chronic otitis media with effusion (OME) and of healthy controls identified Streptococcus salivarius as a health-associated and prevalent inhabitant of the human nasopharynx. However, beneficial potential should be assessed at strain level. Here, we also isolated specific S. salivarius strains from the healthy individuals in our study. These isolates showed a beneficial safety profile and efficacy potential to inhibit OME pathogens in vitro These properties will now have to be evaluated and confirmed in human clinical studies.

Hospital-wide SARS-CoV-2 antibody screening of staff in a university psychiatric centre in Belgium.

In this first serosurvey among psychiatric healthcare providers, only 3.2% of a sample of 431 staff members of a Belgian University Psychiatric Centre, screened 3-17 June 2020, had SARS-CoV-2 immunoglobulin G antibodies, which is considerably lower compared with both the general population and other healthcare workers in Belgium. The low seroprevalence was unexpected, given the limited availability of personal protective equipment and the high amount of COVID-19 symptoms reported by staff members. Importantly, exposure at home predicted the presence of antibodies, but exposure at work did not. Measures to prevent transmission from staff to patients are warranted in psychiatric facilities.

Infant Pneumococcal Carriage in Belgium Not Affected by COVID-19 Containment Measures.

Streptococcus pneumoniae is an important and frequently carried respiratory pathogen that has the potential to cause serious invasive diseases, such as pneumonia, meningitis, and sepsis. Young children and older adults are among the most vulnerable to developing serious disease. With the arrival of the COVID-19 pandemic and the concomitant restrictive measures, invasive disease cases caused by respiratory bacterial species, including pneumococci, decreased substantially. Notably, the stringency of the containment measures as well as the visible reduction in the movement of people appeared to coincide with the drop in invasive disease cases. One could argue that wearing protective masks and adhering to social distancing guidelines to halt the spread of the SARS-CoV-2 virus, also led to a reduction in the person-to-person transmission of respiratory bacterial species. Although plausible, this conjecture is challenged by novel data obtained from our nasopharyngeal carriage study which is performed yearly in healthy daycare center attending children. A sustained and high pneumococcal carriage rate was observed amid periods of stringent restrictive measures. This finding prompts us to revisit the connection between nasopharyngeal colonization and invasion and invites us to look closer at the nasopharyngeal microbiome as a whole.

Immunogenicity and persistence of trivalent measles, mumps, and rubella vaccines: a systematic review and meta-analysis.

BACKGROUND: Despite the universal use of the two-dose trivalent measles-mumps-rubella (MMR) vaccine in the past two decades, outbreaks of these diseases still occur in countries with high vaccine uptake, giving rise to concerns about primary and secondary failure of MMR vaccine components. We aimed to provide seroconversion and waning rate estimates for the measles, mumps, and rubella components of MMR vaccines. METHODS: In this systematic review and meta-analysis we searched PubMed (including MEDLINE), Web of Science, and Embase for randomised controlled trials, cohort studies, or longitudinal studies reporting the immunogenicity and persistence of MMR vaccines, published in English from database inception to Dec 31, 2019. Studies were included if they investigated vaccine-induced immunity in healthy individuals who received a trivalent MMR vaccine, including different dosages and timepoints of vaccine administration. Studies featuring coadministration of MMR with other vaccines, maternal immunity to the MMR vaccine, or non-trivalent formulations of the vaccine were excluded. Pooled seroconversion and waning rates were estimated by random-effects meta-analyses. This study is registered with PROSPERO, CRD42019116705. FINDINGS: We identified 3615 unique studies, 62 (1·7%) of which were eligible for analysis. Estimated overall seroconversion rates were 96·0% (95% CI 94·5-97·4; I2=91·1%) for measles, 93·3% (91·1-95·2; I2=94·9%) for mumps when excluding the Rubini strain, 91·1% (87·4-94·1; I2=96·6%) for mumps when including the Rubini strain, and 98·3% (97·3-99·2; I2=93·0%) for rubella. Estimated overall annual waning rates were 0·009 (95% CI 0·005-0·016; I2=85·2%) for measles, 0·024 (0·016-0·039; I2=94·7%) for mumps, and 0·012 (0·010-0·014; I2=93·3%) for rubella. INTERPRETATION: Our meta-analysis provides estimates of primary and secondary vaccine failure, which are essential to improve the accuracy of mathematical and statistical modelling to understand and predict the occurrence of future measles, mumps, and rubella outbreaks in countries with high vaccine uptake. FUNDING: European Research Council.

No SARS-CoV-2 carriage observed in children attending daycare centers during the intial weeks of the epidemic in Belgium.

To gain knowledge about the role of young children attending daycare in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemic, a random sample of children (n = 84) aged between 6 and 30 months attending daycare in Belgium was studied shortly after the start of the epidemic (February 29th) and before the lockdown (March 18th) by performing in-house SARS-CoV-2 real-time polymerase chain reaction. No asymptomatic carriage of SARS-CoV-2 was detected, whereas common cold symptoms were common (51.2%). Our study shows that in Belgium, there was no sign of early introduction into daycare centers at the moment children being not yet isolated at home, although the virus was clearly circulating. It is clear that more evidence is needed to understand the actual role of young children in the transmission of SARS-CoV-2 and their infection risk when attending daycare.

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.

Infectious diseases epidemiology, quantitative methodology, and clinical research in the midst of the COVID-19 pandemic: Perspective from a European country.

Starting from historic reflections, the current SARS-CoV-2 induced COVID-19 pandemic is examined from various perspectives, in terms of what it implies for the implementation of non-pharmaceutical interventions, the modeling and monitoring of the epidemic, the development of early-warning systems, the study of mortality, prevalence estimation, diagnostic and serological testing, vaccine development, and ultimately clinical trials. Emphasis is placed on how the pandemic had led to unprecedented speed in methodological and clinical development, the pitfalls thereof, but also the opportunities that it engenders for national and international collaboration, and how it has simplified and sped up procedures. We also study the impact of the pandemic on clinical trials in other indications. We note that it has placed biostatistics, epidemiology, virology, infectiology, and vaccinology, and related fields in the spotlight in an unprecedented way, implying great opportunities, but also the need to communicate effectively, often amidst controversy.

Stable HEV IgG seroprevalence in Belgium between 2006 and 2014.

Recent European studies suggest an emergence of hepatitis E virus (HEV) infection. We evaluated trends in birth cohort-specific HEV seroprevalence and regional differences in Belgium. HEV IgG seroprevalence was analysed on national serum banks (1579 and 2087 samples for 2006 and 2014, respectively. Hepatitis E virus antigen was tested on positive samples. Observed data were modelled using a generalized additive model with a complementary log-log link. No significant differences between birth cohorts or sexes were found. Modelling identified the individual's age and province as relevant factors. The probability of HEV seropositivity increases significantly with age. An estimated total of 434 819 (yearly rate of 54,352) (sero-)infections were found between 2006 and 2014. Overall, HEV IgG seroprevalences were 4.1% (64/1579, 95% CI 3.1-5.1) and 5.8% (121/2087, CI 4.8-6.9) in 2006 and 2014, respectively. Observed HEV antigen seroprevalence was 0.027% (1/3666) for the entire cohort. These results show stable HEV IgG seroprevalence in Belgium.

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

BackgroundThe current carriage study was set up to reinforce surveillance during/after the PCV13-to-PCVC10 switch in Belgium.AimThis 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.MethodsA 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).ResultsThe 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%).ConclusionsDuring 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.

Sample size calculation for estimating key epidemiological parameters using serological data and mathematical modelling.

BACKGROUND: Our work was motivated by the need to, given serum availability and/or financial resources, decide on which samples to test in a serum bank for different pathogens. Simulation-based sample size calculations were performed to determine the age-based sampling structures and optimal allocation of a given number of samples for testing across various age groups best suited to estimate key epidemiological parameters (e.g., seroprevalence or force of infection) with acceptable precision levels in a cross-sectional seroprevalence survey. METHODS: Statistical and mathematical models and three age-based sampling structures (survey-based structure, population-based structure, uniform structure) were used. Our calculations are based on Belgian serological survey data collected in 2001-2003 where testing was done, amongst others, for the presence of Immunoglobulin G antibodies against measles, mumps, and rubella, for which a national mass immunisation programme was introduced in 1985 in Belgium, and against varicella-zoster virus and parvovirus B19 for which the endemic equilibrium assumption is tenable in Belgium. RESULTS: The optimal age-based sampling structure to use in the sampling of a serological survey as well as the optimal allocation distribution varied depending on the epidemiological parameter of interest for a given infection and between infections. CONCLUSIONS: When estimating epidemiological parameters with acceptable levels of precision within the context of a single cross-sectional serological survey, attention should be given to the age-based sampling structure. Simulation-based sample size calculations in combination with mathematical modelling can be utilised for choosing the optimal allocation of a given number of samples over various age groups.

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.