de Melker HE; Conyn-van Spaendonck MAE; Schellekens JFP(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1995-11-01)
The objective was to obtain insight into the current incidence of pertussis. Design: Comparison study from different surveillance sources. Method: For the years 1989-1994 the incidence of pertussis was estimated from the number of pertussis notifications, from laboratory data from serodiagnosis, isolations of Bordetella and from the national registration of clinical diagnosis of hospital admissions. Results: The number of notifications and positive serological results yielded similar average annual incidence for the period 1989-1994 (2.3 and 2.2/100,000, respectively). According to notifications peak incidences occurred in 1989 (3.5/100,000) and 1994 (3.4/100,000). For positive serodiagnosis the incidences in 1989 and 1994 were 2.4/100,000 and 3.2/100,0000, respectively. In 1993 the incidence of notifications and positive serodiagnosis (2.4 and 3.2 per 100,000) was also higher than in the other years. The incidence based on hospitalizations, notifications and positive serology was highest among children younger than one year. In 1994 and 1993 the estimations for the vaccine efficacy were 84% (95%-confidence interval 80-87%) and 92% (95%-confidence interval 90-94%), respectively. Conclusion: For 1989-1994, the pattern indicated that pertussis is endemic with four-yearly peaks. The incidence of hospitalizations emphasizes the seriousness of the illness in infants. Due to the vaccine coverage in the Netherlands, the incidence among unvaccinated children is much lower then among unvaccinated children in neighbouring areas with lower vaccine coverage. It is important that general practitioners are aware of the occurrence of pertussis in vaccinated and unvaccinated children and adults. The probable decrease in vaccine efficacy (92% in 1993; 84% in 1994) needs special attention and must be monitored. This stresses the importance of continued surveillance.<br>
de Greeff SC; de Melker HE; Schellekes JFP; Conyn-van Spaendonck MAE(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 2002-04-04)
To gain insight into the incidence and severity of pertussis in the Netherlands in 1999 and 2000, surveillance data based on notifications, laboratory data, hospitalisations and deaths were analysed for these two years and compared to the 1989-1998 period. Results of the paediatric surveillance are also presented here. According to various sources the incidence of pertussis increased in 1999 compared to previous years and decreased again in 2000. The peak incidence according to notifications and positive serology was observed among 4- to 5-year-old children. In 1999 the incidence according to hospital admissions (3.2 per 100,000) was comparable to the incidence during the epidemic of 1996 (3.3 per 100,000) and decreased in 2000 (1.6 per 100,000). The paediatric surveillance showed that most hospitalised children were under one year of age and that complications (apnoea, cyanosis and administration of oxygen) were more frequently reported in the younger age groups. Vaccine efficacy, estimated by the screening method, was higher in 2000 compared to 1997-1999, particularly among 1- and 2-year olds. In conclusion, the incidence of pertussis in 1999 according to notifications increased to reach a higher level than in 1996. In 2000 the incidence decreased again. However, the number of hospital admissions were comparable to the figures for 1996 and 1999, and lower in 2000. Both unvaccinated and vaccinated persons can develop classical pertussis symptoms. Surveillance of pertussis based on various surveillance sources should be continued to monitor the incidence of pertussis and to study the effect of changes in vaccination strategies. Active paediatric surveillance and surveillance of hospital admissions are useful for verifying trends in routine surveillance and describing the severity of pertussis.<br>
de Melker HE; Conyn-van Spaendonck MAE; Schellekens JFP(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1997-09-30)
A sudden and high increase in registrations, positive serodiagnostics, Bordetella isolations and hospital admissions were observed in the Netherlands in 1996. This seems to reflect a true increase in the incidence of pertussis. Most cases occurred among 1-9-year-old vaccinated children. In 1994-1995, and especially 1996 a higher proportion of vaccinated cases was seen among the cases registered. Despite the methodological constraints of vaccine-efficacy estimations using the screening method, a lower vaccine-efficacy for 1996 is probable. The proportion of registrations confirmed with one-point serology in the 1993-96 period which does not meet the formal criteria for registration increased from 25% to 48%. In addition to this 'overreporting', the underreporting of patients with positive two-point serology decreased from 74% in 1993 to 51% in 1996. The number of pertussis patients in 1996 was higher than in 1987. Increased awareness, changes in diagnostics and a lower vaccine coverage could not explain the epidemic. There are indications that changes occurred in the bacterium. This could have resulted in a mismatch between the vaccine-induced immunity and the circulating Bordetella strains. The constant ratio of hospital admissions and notifications and hospital admissions and positive two-point serology among infants less than one year old, indicate no change in the virulence of the circulating strains. In January 1997, active (monthly) surveillance by pediatricians of cases among hospitalized children was started to obtain insight into the severity of pertussis among infants. Protection of these infants is the main reason for pertussis vaccination. The methodological limitations of the current estimations based on the screening method and retrospective data, calls for optimisation of vaccine-efficacy estimations. Therefore a prospective study is considered to assess efficacy of the whole cell vaccine, differentiated by severity of disease, is under consideration.<br>
van den Hof S; Conyn-van Spaendonck MAE; de Melker HE; Geubbels ELPE; Suijkerbuijk AWM; Talsma E; Plantinga AD; Rumke HC(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1998-07-09)
As a result of improved socio-economic state and related hygiene, and the introduction of the National Vaccination Programme (RVP), the incidence of the target diseases of the RVP is low nowadays. Insight in the occurrence of the diseases remains necessary in order to be able to signal possible secondary effects at an early stage. The vaccination coverage is very high in the Netherlands, but considerable geographic differences exist within the country. Especially in municipalities where groups that reject vaccination on religious ground are clustered, the vaccination coverage is low. Herd immunity can be broken in socially and geographically clustered non-vaccinated groups. On the basis of the occurrence results of the target diseases of the RVP, we give recommendations for the future surveillance of the target diseases of the RVP and invasive meningococcal and pneumococcal infections. Besides continuation of the surveillance, additional research in case of outbreaks and epidemics is recommended, in order to obtain more insight into the circulation of the pathogens.<br>
Abbink F; Oomen PJ; Zwakhals SLN; de Melker HE; Ambler-Huiskes A(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 2005-06-07)
This report describes the progress of the National Immunization Programme (NIP) in the Netherlands. Immunization coverage figures as at 1 january 2004 are presented for all vaccines used in the NIP for agecohorts born in 1993, 1998 and 2001.For years national immunization coverage in the Netherlands has been excellent. For 2004 national coverage levels for all vaccines used increased and exceeded 95% for the first time. The slow but steady decrease in coverage for infants reported since 1996 has been restored to a level of coverage exceeding 97%.Although high national immunization coverage can mask variations within country, regional and municipal immunization coverage also improved over the past year. All provinces reported over 90% immunization coverage for all vaccines used and municipal immunization coverage levels below 60%, previously observed each year, were not reported.Areas with low immunization coverage are - once again - concentrated in the so called 'Bible-belt' where groups of orthodox reformed people live who refuse vaccination for religious reasons.In spite of the progress made for the past year under review, joint efforts are still needed to obtain and sustain high immunization coverage. Particularly because it is already known that immunization coverage for the birthcohorts following 2001 was negatively affected by the massive attention paid to the introduction of the new DTaP-IPV-Hib vaccine by the media. Continuous attention and joined efforts of all parties engaged in the NIP will be needed to ensure that the population of the Netherlands is well educated and motivated to have their children immunized.
de Greeff SC; Schellekens JFP; Mooi FR; de Melker HE(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 2004-02-17)
To gain insight into the incidence and severity of pertussis in the Netherlands in 2001 and 2002, surveillance data based on notifications, laboratory data, hospitalisations and deaths were analysed for these two years and compared to that for 1989-2000. The decreasing coverage of serologic data from the LIS-RIVM compared with 1996 was taken into account. According to various surveillance sources pertussis is still endemic with epidemic peaks every two to three years (in 1996, 1999 and 2001). The reported incidence of notified cases was highest in 2001 (50.2/100,000) and decreased in 2002 (28.0). The incidence/100,000 in 2001 calculated from positive two-point serology amounted 4.4 (corrected for decreasing coverage 8.0) and positive one-point serology 30.7 (corrected 55.8) and hospital admissions 2.5. The incidence calculated from these surveillance sources was again lower in 2002: incidence/100,000 positive two-point serology 2.1 (corrected 4.1), positive one-point serology 15.4 (corrected 29.9) and hospitalisations 1.6. Highest incidence of hospitalisations was reported among infants less than 1 year (especially those aged < 3 months). In 2002 the first year an effect of the booster vaccination for four-year-olds might be visible- all surveillance sources showed a decrease in the incidence of cases aged 3 and 4 year old compared with previous years. Besides, small increases in the number of patients older than 5 years were seen. Estimations of vaccine efficacy based on surveillance data showed a slight improvement in vaccine-efficacy for the 1-year-olds in the period 1998-2002 compared with 1996-1997. Still, pertussis is endemic with peaks every 2 to 3 years and with a higher incidence compared to the period prior to the epidemic in 1996-1997. The introduction of the acellular booster-vaccination for 4-year-olds in 2001 has caused a decrease in the incidence of pertussis among the target-population. Long-term surveillance will be necessary to provide insight into the possible effect among the population at large. Estimations of vaccine-efficacy have improved in 1998-2002 compared to 1996-1997, probably as a result of the introduction of a 'stronger' pertussis vaccine in 1997. Pertussis is still most severe among young unvaccinated infants. The latter should be taken into account with the development of future vaccination-strategies (e.g. boostering of parents/care givers).
Neppelenbroek SN; de Melker HE; Schellekens JFP; Rumke HC; Suijkerbuijk AWM; Conyn-van Spaendonck MAE(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1999-06-14)
Objective: To gain insight into the severity of pertussis in hospitalised cases and notifications in relation to the vaccination status and age. Methods: In 1997, hospitalisation data were collected through paediatric surveillance and additional data on notified cases through a questionnaire. Results: From data of 180 hospitalisation admissions collected,42% of the patients were younger than 3 months of age and not vaccinated; 14% were 3-5 months of age and of these, 69% were incompletely vaccinated; 42% were 6 months and older and of these, 70% were vaccinated. Fifty-three percent of the patients were diagnosed as having pertussis, confirmed by a positive culture or PCR, and 44% by positive serology. Two infants, three weeks of age, died. Convulsions (3%), atelectasis (1%) and encephalopathy (1%) occurred among only the very young unvaccinated infants. Young unvaccinated compared to vaccinated children had significantly more frequent cyanosis (77% vs. 40%) and apnoea (22% vs. 5%) and were longer hospitalised (median 12 days vs. 5 days). Additional data were collected from 507 notified cases of which 6% was younger than one year of age; 36% were 1-4 year; 28%, 5-9 years; 10%, 10-15 years; 21%, 16 years and older. Only 7% were unvaccinated; 2% were incompletely vaccinated; 80%, vaccinated and for 11%, the vaccination history was unknown. Eighty-three percent of the pertussis cases were confirmed by positive serology. Most frequently reported symptoms were paroxysmal cough (93%), vomiting (78%), whooping (67%) and shortness of breath (61%). Unvaccinated children reported more frequent cyanosis than vaccinated children (43% vs. 21%) and more hospitalisations (38% vs. 3%). The severity of disease decreased with age. Conclusion: Serious morbidity leading to hospitalisation was reported mainly in young unvaccinated infants less than three months of age. Yet, hospitalisation and classical pertussis also occurred in recently vaccinated children, but the clinical picture was less life threatening.<br>
de Melker HE; van der Peet TE; Berbers WAM; van den Akker R; van Knapen F; Schellekens JFP; Conyn-van Spaendonck MAE(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1995-12-31)
Important information on the occurrence of infectious diseases can be derived from serosurveillance. In 1994 a pilot study for the PIENTER-project was carried out to investigate the feasibility of the establishment of a serum bank representatitive for the Dutch general population. As part of this pilot-study the seroprevalence was measured for mumps, measles, rubella, pertussis, Toxoplasmosis, Toxocara, T. spiralis and Hepatitis A in the 827 participants. The seroprevalences for mumps, measles and rubella was 97,6%, 98,2% and 97,6%, respectively. IgA-antibodies and/or IgG-antibodies against pertussis of at least 5 Units/ml were present for 61,3% and 35,6% of the participants. The seroprevalence for toxoplasma, toxocara and hepatitis A were 43%, 19% and 27,1%, respectively and increased with age. Only two participants had antibodies for T. spiralis. However, due to the small and non-representatitive sample in the pilot, it is impossible to make reliable conclusions. After the large scale nation-wide data collection that will be realised in 1995/1996 reliable seroprevalence estimates for the Dutch general population will become available.<br>
de Melker HE; Suijkerbuijk AWM; Heisterkamp SH; Conyn-van Spaendonck MAE(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 1995-04-30)
INTRODUCTION In 1994 a pilot-study of the so-called PIENTER-project was carried out. The aim of this project is to establish a serum bank of a representative sample of the Dutch population. The serum bank will be used to estimate age-specific immunity of the general population against childhood diseases of the Netherlands Immunisation Programme, the incidence of infectious diseases with a frequent subclinical course and the prevalence of serum-derterminants of other illnesses. The questionnaire used in the pilot-study was evaluated in order to develop a questionnaire for the nation-wide data collection. AIM Evaluation of the questionnaire used for data collection in a pilot of a cross-sectional population-based study in the province of Utrecht. METHODS A sample of four municipalities weighted by the number of inhabitants was taken out of the municipalities in the Province of Utrecht. 510 persons in the age strata 0, 1-4, 5-9 to 75-79 years were randomly selected from the populations registers of these four municipalities. The participants have been asked to give some blood and to fill in a questionnaire. They have been requested to bring their vaccination certificates of the Dutch immunisation programme, of vaccination on the occasion travelling to the tropics and of military service. These vaccination data were registered on a study form. The opinion of the participants on the length and clarity of the questionnaire and the frequency of missing values for all questions were described. The population proportions weighted by age for self-reported vaccination history and the relation with religion were given. Self-reported vaccination history for diphteria, pertussis, tetanus, poliomyelitis and mumps, measles and rubella was compared with information on the vaccination history derived from the vaccination certificate of the Dutch immunisation programme. The proportions weighted by age for self-perception of health status, nationality and level of education were compared with the figures of the Netherlands Central Bureau of Statistics for the Dutch general population. The expected number of persons in subgroups for level of education, religion, nationality, ethnicity and participation on the Dutch immunisation programme in the nation-wide study were calculated on the basis of results of the pilot. In order to calculate the expected precision of the estimates of the seroprevalence in these subgroups to be reached in the nation-wide study, the serological results for hepatitis A in the pilot were used. RESULTS AND CONCLUSIONS The results confirm a difference in vaccination history and attitude of persons who belong to specific religious groups who reject vaccination. These persons reported more frequent that they were not (completely) vaccinated and adhere more often the opinion that vaccination was not necessary. They also reported more frequently principal refusal as the reason for incomplete vaccination. However, most persons who belong to a religion from which it is known that vaccination is refused, reported that vaccination was completed. As religion and vaccination history are correlated, it is important for the analysis of seroprevalence data to collect data on religion. The self-reported vaccination history for diphtheria, pertussis, tetanus, poliomyelitis, mumps, measles and rubella did not agree with the vaccination certificates of the Dutch immunisation programme. Participants frequently reported that the questions on vaccination history were not clear to them. Therefore in the nation-wide study questions on vaccination history will be limited. Information on vaccination history registered in the vaccination certificates of the Dutch immunisation programme will be collected. In comparison with the figures from the Central Bureau of Statistics persons without the Dutch nationality were underrepresented in the pilot of the Pienter-project. The participants of the Pienter-project might have been not representative for the level of education. The self-perception of health status were comparable with the Central Bureau of Statistics. The precision of seroprevalence to be expected in the nation-wide data collection seems reliable for subgroups of sex, level of education and persons who report to have participated in the Dutch immunisation programme. In contrast no subgroup analysis (unless special actions are taken to increase the response) will be possible for persons with a non-Dutch nationality or ethnicity. For reliable seroprevalence estimates for persons (younger than 40 year) who have not participated in the Dutch Immunisation Programme and persons who belong to a religion from which it is known that vaccination is refused research has to be carried out in municipalities with a low vaccin coverage such that the number of persons in these subgroups will increase.<br>
de Melker HE; Neppelenbroek SN; Schellekens JFP; Suijkerbuijk AWM; Conyn-van Spaendonck MAE(Rijksinstituut voor Volksgezondheid en Milieu RIVM, 2000-06-16)
Objective: To gain insight into the severity of pertussis in hospitalised cases. Methods: In 1998, hospitalisation data were collected through paediatric surveillance. Results: From 115 hospitalisation admissions collected, 55% of the patients were younger than 3 months of age and not vaccinated; 12% were 3-5 months of age and of these, 50% were incompletely vaccinated; 33% were 6 months and older and of these, 61% were vaccinated. Fourty-six percent of the patients were diagnosed as having pertussis, confirmed by a positive culture or PCR, and 44% by positive serology. Three unvaccinated cases less than three months old died. Cyanosis, apnoea, administration of oxygen, artifical respiration and bradycardia were more frequently reported for unvaccinated cases compared to vaccinated cases and the hospitalisation time was longer (median 10 days vs. 4.5 days). Although complications were not often reported for vaccinated cases, the only case with encephalopathy was vaccinated and 17% of vaccinated cases had pneumonia. Conclusion: The lower number of reported cases in 1998 seems to reflect the lower pertussis incidence that was also observed in routine surveillance of notifications and cases with positive serology. Like in 1997 pertussis was most severe and complications were more frequently reported in young unvaccinated infants less than three months of age. However, also typical and severe pertussis cases occurred among vaccinated individuals. Active monthly paediatric surveillance is useful to verify trends in routine surveillance; interpretation of the routine sources is hampered by changes in the notification law and decentralisation of serology.<br>
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