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R de Groot

Publications and source records attributed to R de Groot.

At least 19 recordsLinked to original sources
PubMed2006

[Chickenpox: sufficient reasons for the introduction of vaccination].

The incidence of chickenpox and its complications is high enough to favour introducing varicella vaccination into the Dutch immunisation programme for children, although current Dutch figures may even underestimate the incidence. Safe and effective MMRV vaccines, in which varicella (V) vaccine is combined with measles, mumps and rubella (MMR), could well replace the MMR vaccine used at present. MMRV vaccines should be administered subcutaneously in two doses. Ten years after the introduction of varicella vaccination in the United States of America, the incidence of complications has decreased impressively. An effect on the incidence of herpes zoster has not (yet) been seen.

Chickenpox↗
PubMed2006

Dynamics of pneumococcal colonization in healthy Dutch children.

A recent study of pneumococcal colonization in 3198 healthy children of 1-19 years of age in The Netherlands showed pneumococcal colonization in 19 % of the children, with a peak incidence of 55 % at the age of 2 years; an age-related serotype distribution was also found. In the present study, the genetic background and resistance profiles of 578 pneumococcal isolates from the latter study were characterized by means of chromosomal genotyping and susceptibility testing. In contrast to the age-related serotype distribution observed previously, the genetic background of the strains was not age related. Few strains were found showing close homology (>95 %) with the international clones Spain(9V)-3 (ten isolates showed homology), England(14)-9 (four isolates), Tennessee(23F)-4 (two isolates), CSR(14)-10 (one isolate) and Sweden(15A)-25 (one isolate). In total, 19 % of strains showed resistance to one or more antibiotics. Resistance to cotrimoxazole, tetracycline, erythromycin and penicillin was found in 12.9, 5.6, 5.0 and 2.7 % of isolates, respectively. Multidrug resistance was found in 1.9 % of strains. In conclusion, pneumococcal colonization isolates from healthy Dutch children represent a heterogeneous, mostly antibiotic susceptible, genetic population.

Adolescent↗
PubMed2005

Pneumococcal conjugate vaccination does not induce a persisting mucosal IgA response in children with recurrent acute otitis media.

AIM: In a prospective controlled study in young children with a history of recurrent acute otitis media, we analyzed the salivary IgA and IgG antibody titers upon vaccination with a 7-valent pneumococcal conjugate vaccine (PCV) given once or twice, followed by a 23-valent polysaccharide booster vaccination. METHODS: Salivary IgA and IgG antibody concentrations to vaccine serotype 6B, 14, 18C and 19F were measured by enzyme immunoassay in 38 samples of children vaccinated with PCV and 45 control samples. In the PCV group, 12 samples were taken prior to vaccination, 12 samples 4 weeks after the polysaccharide booster (8 months after the first conjugate vaccination) and 14 samples 7 months after the last vaccination (14 months after the first conjugate vaccination). In the control group 15 children were sampled at each of these three time points. RESULTS: We observed an increase in salivary IgG antibody concentrations against serotype 6B, 14, and 18C 14 months after the primary vaccination in children vaccinated with PCV twice, although this was significant for serotype 14 only. There was no increase in salivary IgG antibody in children vaccinate with PCV once nor in control children. IgA antibody titers increased significantly after 8 and after 14 months in both the pneumococcal vaccine recipients and the controls. However, the observed increase in mean antibody titers was significantly higher in control children compared to the PCV group. CONCLUSION: We suggest that repeated pneumococcal conjugate vaccination is necessary to induce an increase in salivary IgG antibodies and effectuate clearance of S. pneumoniae from the nasopharyngeal mucosa of children with recurrent acute otitis media. We hypothesize that the increase in salivary IgA is caused by the local boosting of the mucosal immune response by carriage and recurrent infections, which occurs less often in the PCV group compared to the control children.

Child↗
PubMed2005

Epidemiology of nasopharyngeal carriage of Neisseria meningitidis in healthy Dutch children.

We investigated the prevalence and determinants of nasopharyngeal carriage of Neisseria meningitidis in 3200 healthy children aged 1-19 years. The incidence of meningococcal carriage was, on average, 1.5%. Peak incidences were seen at age 1 year and after age 15 years. The independent determinants of meningococcal carriage included age, regular visits to youth clubs (odds ratio [OR], 2.2) and discotheques (OR, 4.3), and pneumococcal carriage (OR, 4.1).

Adolescent↗
PubMed2005

Molecular epidemiology of pneumococcal colonization in response to pneumococcal conjugate vaccination in children with recurrent acute otitis media.

A randomized double-blind trial with a 7-valent pneumococcal conjugate vaccine was conducted in The Netherlands among 383 children, aged 1 to 7 years, with a history of recurrent acute otitis media. No effect of vaccination on the pneumococcal colonization rate was found. However, a shift in serotype distribution was clearly observed (R. Veenhoven et al., Lancet 361:2189-2195, 2003). We investigated the molecular epidemiology of 921 pneumococcal isolates retrieved from both the pneumococcal vaccine (PV) and control vaccine (CV) groups during the vaccination study. Within individuals a high turnover rate of pneumococcal restriction fragment end labeling genotypes, which was unaffected by vaccination, was observed. Comparison of the genetic structures before and after completion of the vaccination scheme revealed that, despite a shift in serotypes, there was clustering of 70% of the pneumococcal populations. The remaining isolates (30%) were equally observed in the PV and CV groups. In addition, the degree of genetic clustering was unaffected by vaccination. However, within the population genetic structure, nonvaccine serotype clusters with the serotypes 11, 15, and 23B became predominant over vaccine-type clusters after vaccination. Finally, overall pneumococcal resistance was low (14%), and, albeit not significant, a reduction in pneumococcal resistance as a result of pneumococcal vaccination was observed. Molecular surveillance of colonization in Dutch children shows no effect of pneumococcal conjugate vaccination on the degree of genetic clustering and the genetic structure of the pneumococcal population. However, within the genetic pneumococcal population structure, a clear shift toward nonvaccine serotype clusters was observed.

Acute Disease↗
PubMed2005

Use of pooled urine samples and automated DNA isolation to achieve improved sensitivity and cost-effectiveness of large-scale testing for Chlamydia trachomatis in pregnant women.

The success of large-scale screening for Chlamydia trachomatis depends on the availability of noninvasive samples, low costs, and high-quality testing. To evaluate C. trachomatis testing with pregnant women, first-void urine specimens from 750 consecutive asymptomatic pregnant women from the Rotterdam area (The Netherlands) were collected. Initially, we investigated the performance of three different DNA isolation methods with 350 of these urines and 70 pools of 5 of the same subset of urine samples. The routinely used COBAS AMPLICOR test was compared to the COBAS AMPLICOR test with prior DNA isolation by use of the MagNA Pure large-volume kit and the MagNA Pure bacterial DNA isolation kit. The latter combination provided the best DNA test for pooled urines, with a sensitivity twice that of the other methods. Next, using all 750 urines, the COBAS AMPLICOR performance for individual testing was compared to pooled testing with the standard COBAS AMPLICOR procedure and subsequently to pooled testing with COBAS AMPLICOR in combination with the MagNA Pure bacterial DNA isolation kit. The sensitivity of COBAS AMPLICOR was 65% on individual and 42% on pooled urines but improved to 92% on pooled urines with the MagNA Pure bacterial DNA isolation kit, making this combination the best screening method. The C. trachomatis prevalence in this population appeared to be 6.4%. Additionally, the cost of the combined MagNA Pure bacterial DNA isolation kit and COBAS AMPLICOR method on pooled urines was only 56% of the cost of the standard COBAS AMPLICOR test applied to individual urines. Costs per positive case detected in the combined method were 39% of standard costs.

Automation↗
PubMed2004

No epidemiological evidence for infant vaccinations to cause allergic disease.

CONTEXT: The prevalence of allergic diseases has increased considerably over the last decades. The hygiene hypothesis has emerged, linking reduced microbial exposure and infections early in life with the development of allergic diseases. Especially some of currently available non-replicating infant vaccines are unlikely to mimic a natural infection-mediated immune response that protects against the development of allergic diseases. Moreover, several studies suggested infant vaccinations to increase the risk of allergic diseases. OBJECTIVE: To determine whether infant vaccinations increase the risk of developing allergic disease. DATA SOURCES: We searched MEDLINE from 1966 to March 2003 and bibliography lists from retrieved articles, and consulted experts in the field to identify all articles relating vaccination to allergy. STUDY SELECTION AND DATA EXTRACTION: We selected epidemiological studies with original data on the correlation between vaccination with diphtheria, pertussis, tetanus (DPT), measles, mumps, rubella (MMR) and Bacillus Calmette-Guérin (BCG) vaccine in infancy and the development of allergic diseases, and assessed their quality and validity. DATA SYNTHESIS: Methodological design and quality varied considerably between the studies we reviewed. Many studies did not address possible confounders, such as the presence of lifestyle factors, leaving them prone to bias. The studies that offer the stronger evidence, including the only randomized controlled trial at issue published to date, indicate that the infant vaccinations we investigated do not increase the risk of developing allergic disease. Furthermore, BCG does not seem to reduce the risk of allergies. CONCLUSIONS: The reviewed epidemiological evidence indicates that, although possibly not contributing to optimal stimulation of the immune system in infancy, current infant vaccines do not cause allergic diseases.

BCG Vaccine↗
PubMed2004

Colony blot assay: a useful method to detect multiple pneumococcal serotypes within clinical specimens.

The efficacy of pneumococal conjugate vaccines in young children may be complicated by serotype replacement. We developed a colony blot assay which enables the identification of re-colonization with novel serotypes (replacement), overgrowth by minor co-colonizing serotypes or suppression of previously predominant vaccine serotype strains as a result of vaccination. This method allows the identification of multiple serotypes in a single specimen in a ratio of 1:1000. In order to demonstrate the potential of our method, we investigated the consecutive nasopharyngeal samples of 26 children who had shown a shift in pneumococcal colonization after conjugate vaccination. Mixed colonization was found once in 15 pre-vaccination samples and four times in 26 post-vaccination samples. In the remaining children 'true replacement' had presumably occurred. Hence, we conclude that the colony blot assay is an easy to apply method, which allows the identification of different pneumococcal serotypes within single clinical specimens.

Carrier State↗
PubMed2004

Colonisation by Streptococcus pneumoniae and Staphylococcus aureus in healthy children.

A trial with a 7-valent pneumococcal-conjugate vaccine in children with recurrent acute otitis media showed a shift in pneumococcal colonisation towards non-vaccine serotypes and an increase in Staphylococcus aureus-related acute otitis media after vaccination. We investigated prevalence and determinants of nasopharyngeal carriage of Streptococcus pneumoniae and S aureus in 3198 healthy children aged 1-19 years. Nasopharyngeal carriage of S pneumoniae was detected in 598 (19%) children, and was affected by age (peak incidence at 3 years) and day-care attendance (odds ratio [OR] 2.14, 95% CI 1.44-3.18). S aureus carriage was affected by age (peak incidence at 10 years) and male sex (OR 1.46, 1.25-1.70). Serotyping showed 42% vaccine type pneumococci. We noted a negative correlation for co-colonisation of S aureus and vaccine-type pneumococci (OR 0.68, 0.48-0.94), but not for S aureus and non-vaccine serotypes. These findings suggest a natural competition between colonisation with vaccine-type pneumococci and S aureus, which might explain the increase in S aureus-related otitis media after vaccination.

Acute Disease↗
PubMed2004

Pneumococcal vaccines: an update on current strategies.

Streptococcus pneumoniae is a major cause of morbidity and mortality in infants, children and the elderly. Despite the availability of excellent antimicrobial therapy and adequate health care systems, respiratory diseases and invasive infections caused by pneumococci still comprise a major health problem. The emerging resistance to penicillin and other commonly used antibiotics underscores the importance of the development of novel vaccine strategies to combat pneumococcal disease. Although the 23-valent polysaccharide (PS) vaccine is immunogenic and protective in most adults and children over 5 years of age, they fail to protect children under 2 years of age. Fortunately, the recent conjugate vaccines have shown to be highly efficacious in preventing invasive diseases in this risk group. Moreover, promising results regarding prevention of pneumonia and acute otitis media have been published. Unfortunately, protection is raised against a limited number of pneumococcal serotypes, and serotype replacement and subsequent vaccine failure have become a serious concern. Currently, several pneumococcal surface proteins are considered as alternative vaccine candidates because of their serotype-independence. Thus far, pneumococcal surface adhesin A (PsaA) has proven to be highly protective against colonization in animal models. Moreover, pneumococcal surface protein A (PspA) and pneumolysin have shown to elicit protection against invasive diseases. Future research will elucidate their true potential in protecting humans. In this paper we discuss the present knowledge on pneumococcal vaccines and the current status of novel vaccine strategies.

Adhesins, Bacterial↗
PubMed2004

Pharmacokinetics of indinavir combined with low-dose ritonavir in human immunodeficiency virus type 1-infected children.

So far, no pediatric doses for indinavir combined with ritonavir have been defined. This study evaluated the pharmacokinetics of 400 mg of indinavir/m(2) combined with 125 mg of ritonavir/m(2) every 12 h (q12h) in 14 human immunodeficiency virus type 1-infected children. The area under the concentration-time curve from 0 to 24 h and the minimum concentration of drug in serum for indinavir were similar to those for 800 mg of indinavir-100 mg of ritonavir q12h in adults, while the maximum concentration of drug in serum was slightly decreased, with geometric mean ratios (90% confidence intervals in parentheses) of 1.1 (0.87 to 1.3), 0.96 (0.60 to 1.5), and 0.80 (0.68 to 0.94), respectively.

Adult↗
PubMed2004

The Ami-AliA/AliB permease of Streptococcus pneumoniae is involved in nasopharyngeal colonization but not in invasive disease.

The Ami-AliA/AliB oligopeptide permease is an ATP-binding cassette transporter which is found in Streptococcus pneumoniae and which is involved in nutrient uptake. We investigated the role of the three paralogous oligopeptide-binding lipoproteins AmiA, AliA, and AliB by using murine models of pneumococcal colonization and invasive disease. A series of mutants lacking aliA, aliB, and amiA either alone or in combination as double or triple mutations were used. Inoculation of the nasopharynx with a mixture of the obl (oligopeptide-binding lipoprotein-negative) triple-mutant and wild-type (D39) bacteria resulted in significantly smaller numbers of obl bacteria colonizing the nasopharynx. The use of a mixture of individual mutants and wild-type pneumococci revealed that AmiA, AliA, and AliB were all required for successful colonization of the nasopharynx. The obl mutant was more attenuated than the aliB mutant but not the aliA or amiA mutant. Therefore, there is some redundancy in the Ami-AliA/AliB complex in terms of nasopharyngeal colonization, with AliA and AmiA being able to compensate for the removal of AliB. Animals with invasive disease caused by these mutants had survival times, bacterial loads, and inflammatory cytokine production levels similar to those of animals infected with wild-type pneumococci. Our results show that although the Ami-AliA/AliB complex is not required for virulence during pneumococcal pneumonia, it does play a role in colonization of the nasopharynx.

Animals↗
PubMed2003

Changes in indinavir exposure over time: a case study in six HIV-1-infected children.

OBJECTIVE: To study changes in indinavir exposure over time in HIV-1-infected children. MATERIALS AND METHODS: Protease inhibitor (PI)-naive HIV-1-infected children were treated with indinavir, zidovudine and lamivudine. Steady-state plasma pharmacokinetic (PK) sampling was carried out as standard of care. The AUC(0-8) was targeted between 15 and 30 mg h/L. PK sampling was repeated after dosage adjustment until the AUC(0-8) reached target values. Patients were included when the time interval between PK samplings was > or =2 years and differences in dosage/m2 <10% between PK samplings 1 and 2. Corrections of dose for changes in body size were carried out. RESULTS: Six children were enrolled with a median age of 5.2 years (range 1.7-13.6 years). All had a viral load below 500 copies/mL. The geometric mean (GM) of the AUC(0-8) decreased from 25.3 mg h/L at the first PK-day to 19.1 mg h/L at the second PK-day [geometric mean ratio (GMR): 0.76 (95% C.I.: 0.48-1.20)]. The GM of Cmax decreased from 11.8 to 10.4 mg/L [GMR: 0.88 (95% C.I.: 0.59-1.32)]. The GM of Cmin decreased from 0.08 to 0.07 mg/L [GMR: 0.86 (95% C.I.: 0.62-1.18)]. All children had an AUC(0-8) above 15 mg h/L on the first PK-day; three had an AUC(0-8) below 15 mg h/L on the second PK-day. In two of these three children, the plasma viral load was >500 copies/mL. CONCLUSION: Changes in indinavir exposure were observed over time. In two patients, decreased indinavir exposure was associated with virological failure. Therapeutic drug monitoring should be carried out over time since this may prevent subtherapeutic dosing in children.

Adolescent↗
PubMed2003

Host genetic determinants of Neisseria meningitidis infections.

The clinical presentation of infections caused by Neisseria meningitidis is highly diverse. Some patients develop meningitis, and others present with sepsis or even septic shock. After invasion of the bloodstream by the bacteria, three main cascade pathways are activated. These are the complement system, the inflammatory response, and the coagulation and fibrinolysis pathway. These pathways do not act independently but are able to interact with each other. Genetic polymorphisms among components of these pathways have been shown to be involved in the susceptibility, severity, and outcome of meningococcal disease. We review knowledge of genetic variations associated with susceptibility to and severity of meningococcal infection. Complement deficiencies and defects in sensing or opsonophagocytic pathways, such as the rare Toll-like receptor 4 single nucleotide polymorphisms (SNPs) and combinations of inefficient variants of Fcgamma-receptors, seem to have the most important role in genetically established susceptibility. Effect on severity has repeatedly been reported for FcgammaRIIa and plasminogen activator inhibitor type 1 (PAI1) polymorphisms. Outcome effects have been confirmed for SNPs in properdin deficiencies, PAI1 and combination of the -511C/T SNP in interleukin 1beta, and the +2018C/T SNP in interleukin RN. Conflicting results are reported for the effect of the -308G/A promoter polymorphism in tumour necrosis factor (TNF) alpha. These differences may reflect discrepancies in group definitions between studies or the influence of additional SNPs in the TNFalpha promoter, which can form haplotypes representing different cytokine production capacity. For several SNPs, the potential effect on susceptibility, severity, or outcome has not yet been confirmed in an independent study.

Child↗
PubMed2003

Cross-reactivity of antibodies against PorA after vaccination with a meningococcal B outer membrane vesicle vaccine.

The cross-reactivity of PorA-specific antibodies induced by a monovalent P1.7-2,4 (MonoMen) and/or a hexavalent (HexaMen) meningococcal B outer membrane vesicle vaccine (OMV) in toddlers and school children was studied by serum bactericidal assays (SBA). First, isogenic vaccine strains and PorA-identical patient isolates were compared as a target in SBA, to ensure that the vaccine strains are representative for patient isolates. Geometric mean titers (GMTs) in SBA against patient isolates with subtypes P1.5-2,10 and P1.5-1,2-2 after vaccination with HexaMen were generally lower than those against vaccine strains with the same subtype, although the percentage of vaccine responders (> or =4-fold increase in SBA after vaccination) was not affected. Using various P1.7-2,4 patient isolates, GMTs as well as the number of vaccine responders were higher than for the P1.7-2,4 vaccine strain, indicating that the use of the P1.7-2,4 vaccine strain may have underestimated the immunogenicity of this subtype in HexaMen. Secondly, the cross-reactivity of antibodies induced by MonoMen and HexaMen was studied using several patient isolates that differed from the vaccine subtypes by having minor antigenic variants of one variable region (VR), by having a completely different VR or by having a different combination of VRs. MonoMen induced P1.4-specific antibodies that were cross-reactive with P1.4 variants P1.4-1 and P1.4-3. HexaMen induced a broader cross-reactive antibody response against various patient isolates with one VR identical to a vaccine subtype or a combination of VRs included in HexaMen. Cross-reactivity, measured by a fourfold increase in SBA after vaccination, against these strains ranged from 23 to 92% depending on the subtype of the tested strain and was directed against both VR1 and VR2. The extended cross-reactivity of vaccinee sera induced by HexaMen against antigenic variants has important favorable implications for meningococcal B OMV vaccine coverage.

Amino Acid Sequence↗
PubMed2002

[Reduction of vertical transmission by means of perinatal prophylaxis in the case of children exposed to HIV-1 and born in the Netherlands during the period 1995-1999].

OBJECTIVE: Registration of the number of children born to HIV-infected mothers diagnosed prepartum and analysis of the efficacy of the policy for preventing mother-to-child transmission of HIV-1 in the period 1995 to 1999. DESIGN: Prospective. METHOD: On a monthly basis, Dutch paediatricians reported HIV-1 exposed children to the Dutch Paediatric Surveillance Unit. All reports were followed up with standard questionnaires. An additional retrospective study was performed because of incomplete registration. Paediatricians in centres for the care of HIV-infected patients were requested to retrospectively report HIV-exposed children. The standard questionnaires were submitted to these paediatricians. Data were collected during the period 1 January 1995-31 December 1999. RESULTS: The number of children known to be exposed to HIV-1 and for whom the mother was diagnosed prepartum, increased from 5 to 25 per year. The percentage of HIV-1 infected children decreased from 20% (1/5) to 4% (1/25). The number of pregnant HIV-1 infected women using highly active antiretroviral therapy increased during the study period from 0% (0/5) to 72% (18/25). Antiretroviral therapy was administered to 92% (23/25) of HIV-1 exposed children. In total 2% of the children received breastfeeding. CONCLUSION: Despite an increase in the number of children known to be exposed to HIV-1, a decrease in the percentage of HIV-1-infected children was observed. Of the children born in 1999 and known to be exposed to HIV-1, 4% were infected. Measures taken in the Netherlands to prevent mother-to-child transmission of HIV-1 infection are effective.

Antiretroviral Therapy, Highly Active↗
PubMed2002

[Epidemiological characteristics of reported HIV-1 infection in children in the Netherlands, 1998-2000: vertical transmission via parents from countries with a generalised epidemic].

OBJECTIVE: To document the course and characteristics of the annual new diagnoses of HIV-1 infection in children in the Netherlands. DESIGN: Prospective registration from January 1, 1998 till December 31, 2000. METHODS: Dutch paediatricians reported HIV-positive children to the Dutch Paediatric Surveillance Unit on a monthly basis. All reports were followed up with standard questionnaires. RESULTS: During the period 1998-2000, 42 children were diagnosed with HIV-1 infection. This number was almost equal to the number of HIV-1 infected children diagnosed during the period 1995-1997 (n = 43). In 86% of the children one or both parents originated from a country with a generalised HIV epidemic. In the case of two children (5%), both parents were of Dutch origin. Most children (81%) were infected by mother-to-child transmission. Of these children, 48% (n = 20) were born in the Netherlands. Forty percent of the children born in the Netherlands and infected through vertical transmission lived in one of the four big cities of the Netherlands (Amsterdam, Rotterdam, The Hague and Utrecht). The remaining 60% were distributed across almost all the Dutch provinces. CONCLUSIONS: The increase in the number of newly-infected children in 1995-1997 appears to have reached a plateau in 1998-2000, possibly as a result of a more active detection and treatment policy amongst pregnant women in at-risk groups. However, the 20 newly infected children born in the Netherlands indicate that this policy aimed at preventing vertical transmission is not yet being fully implemented.

Child↗