Persistence of pertussis in an immunized population: results of the Nova Scotia Enhanced Pertussis Surveillance Program

Estimation of vaccine effectiveness using the screening method

The screening method provides a simple and rapid way of estimating vaccine effectiveness. This paper discusses the validity of the screening method with particular reference to bias and precision. Methods for correcting confounding, adjusting for covariates and over-dispersion, and deriving confidence limits are discussed in a modelling framework. The methods are illustrated using data on measles and pertussis vaccines.

Structural basis for antibody binding to adenylate cyclase toxin reveals RTX linkers as neutralization-sensitive epitopes

RTX leukotoxins are a diverse family of prokaryotic virulence factors that are secreted by the type 1 secretion system (T1SS) and target leukocytes to subvert host defenses. T1SS substrates all contain a C-terminal RTX domain that mediates recruitment to the T1SS and drives secretion via a Brownian ratchet mechanism. Neutralizing antibodies against the Bordetella pertussis adenylate cyclase toxin, an RTX leukotoxin essential for B. pertussis colonization, have been shown to target the RTX domain and prevent binding to the α_Mβ₂ integrin receptor. Knowledge of the mechanisms by which antibodies bind and neutralize RTX leukotoxins is required to inform structure-based design of bacterial vaccines, however, no structural data are available for antibody binding to any T1SS substrate. Here, we determine the crystal structure of an engineered RTX domain fragment containing the α_Mβ₂-binding site bound to two neutralizing antibodies. Notably, the receptor-blocking antibodies bind to the linker regions of RTX blocks I–III, suggesting they are key neutralization-sensitive sites within the RTX domain and are likely involved in binding the α_Mβ₂ receptor. As the engineered RTX fragment contained these key epitopes, we assessed its immunogenicity in mice and showed that it elicits similar neutralizing antibody titers to the full RTX domain. The results from these studies will support the development of bacterial vaccines targeting RTX leukotoxins, as well as next-generation B. pertussis vaccines.

Diverse bacterial pathogens use the type 1 secretion system (T1SS) to secrete RTX leukotoxins, which target host leukocytes during infection. T1SS substrates all contain a repetitive C-terminal ‘RTX’ domain that adopts a characteristic β-roll fold and is involved in secretion. Notably, The RTX domain of Bordetella pertussis adenylate cyclase toxin (ACT) mediates leukocyte targeting via binding to the α_Mβ₂ integrin receptor, and antibodies that block receptor binding neutralize toxin activity. However, ACT also contains multiple non-neutralizing epitopes, and precise knowledge of the sites targeted by neutralizing antibodies is desirable for vaccine design. Here we determine the crystal structure of an ACT fragment in complex with two neutralizing antibodies and define the key neutralization-sensitive sites within the RTX domain. This first structure of a heterotypic protein–protein interaction formed by an RTX domain suggests the linker regions between β-roll segments engage binding partners.

Pertussis vaccine effectiveness and duration of protection - A systematic review and meta-analysis

A comprehensive review of observational pertussis vaccine effectiveness (VE) studies is needed to update gaps from previous reviews. We conducted a systematic review of VE and duration of protection studies for the whole-cell (wP) and acellular (aP) pertussis vaccines and conducted a formal meta-analysis using random effects models. Evidence continues to suggest that receipt of any pertussis vaccine confers protection in the short-term against disease although this protection wanes rapidly for aP vaccine. We detected significant heterogeneity in pooled estimates due, in part, to factors such as bias and confounding which may be mitigated by study design. Our review of possible sources of heterogeneity may help interpretation of other VE studies and aid design decisions in future pertussis VE research.

Revisiting the epidemiology of pertussis in Canada, 1924-2015: a literature review, evidence synthesis, and modeling study

BACKGROUND

Disease surveillance is central to the public health understanding of pertussis epidemiology. In Canada, public reporting practices have significantly changed over time, creating challenges in accurately characterizing pertussis epidemiology. Debate has emerged over whether pertussis resurged after the introduction of adsorbed pertussis vaccines (1981-1985), and if the incidence fell to its pre-1985 after the introduction of acellular pertussis vaccines (1997-1998). Here, we aim to assemble a unified picture of pertussis disease incidence in Canada.

METHODS

Using publicly available pertussis surveillance reports, we collected, analyzed and presented Canadian pertussis data for the period (1924-2015), encompassing the pre-vaccine era, introduction of vaccine, changes to vaccine technology, and the introduction of booster doses. Information on age began to be reported since 1952, but age reporting practices (full, partial or no ages) have evolved over time, and varied across provinces/territories. For those cases reported without age each year, we impute an age distribution by assuming it follows that of the age-reported cases.

RESULTS

Below the age of 20 years, the adjusted age-specific incidence from 1969 to 1988 is substantially higher than existing estimates. In children < 1 year, the incidence in some years was comparable to that during the 1988-1999 resurgence.

CONCLUSIONS

The results presented here suggest that the surge in the average yearly incidence of pertussis that began in 1988 was weaker than previously inferred, and in contrary to the past findings, below age 5, the average yearly incidence of pertussis from 1999 to 2015 (when the incidence dropped again) has been lower than it was from 1969 to 1988.

Assessing adolescent immunization options for pertussis in Canada: A cost-utility analysis

BACKGROUND

Adolescent tetanus, diphtheria and pertussis (Tdap) immunization helps prevent pertussis infection. Timing of Tdap receipt represents an important facet of successful adolescent pertussis immunization. Potential strategies for timing of vaccine administration are each associated with different benefits - including disease prevention - and costs. The objective of this study was to assess the cost-utility of adolescent pertussis immunization strategies in Canada.

METHODS

A cost-utility analysis was conducted using a pertussis disease history-simulating Markov model, with adolescents (beginning at age 10 years) as the cohort of interest. The model assessed three Tdap vaccination strategies: (1) immunization of 10 year olds, (2) removal of adolescent vaccination, and (3) immunization of 14 year olds (status quo). The analysis was conducted from a healthcare payer perspective and used a lifetime time horizon. Primary outcomes included life years, quality-adjusted life years (QALYs), health system costs, and an incremental cost-effectiveness ratio (ICER). Costs and outcomes were discounted at 1.5 percent annually. Deterministic and probabilistic sensitivity analyses were performed to assess parameter uncertainty.

RESULTS

The current recommended adolescent immunization strategy (at age 14) resulted in an average of 40.4432 expected QALYs and $26.28 per individual. This strategy was dominated by immunization at 10 years and no immunization. Compared to no immunization, immunizing adolescents at age 10 had an ICER of $74,899 per QALY. Results were most sensitive to the incidence of pertussis and the utility of moderate or severe pertussis. At a cost-effectiveness threshold of $50,000/QALY, removal of adolescent vaccination represented the most cost-effective strategy in 78% of simulations.

CONCLUSION

Analysis assumes a policy context where immunization of pregnant women is recommended. Findings suggest that alternate adolescent Tdap vaccine strategies - either immunization of 10 year olds, or removal of the adolescent vaccine - are more cost-effective than the current practice of immunizing 14 year olds.

Prevention of pertussis: An unresolved problem

Pertussis is a highly contagious respiratory disease caused by Bordetella pertussis. However, after the introduction of the whole-cell pertussis vaccine (wP), the annual incidence rates of the disease progressively declined. Despite this result, the inclusion of wP in the national immunization schedule of infants and young children was debated regarding its safety. Several efforts to produce vaccines based on B. pertussis components capable of evoking protective immunity with no or limited adverse events were made. Of these others, five pertussis antigens were considered possible components of acellular vaccines (aPs): pertussis toxin (PT), filamentous haemagglutinin (FHA), pertactin (PRN) and fimbria proteins 2 and 3. However, the introduction of aPs was followed by a slight but progressive increase in the incidence of pertussis. This paper discusses the potential reasons for reduced aPs efficacy. Moreover, it attempts to evaluate the real effectiveness of aPs and the potential differences between available preparations. Data analysis showed that several boosters are needed to maintain protection against pertussis and additional studies are needed to confirm the antigens that should be included in aPs to improve the prevention of pertussis.

Bordetella pertussis

Pertussis is a highly infectious vaccine-preventable cough illness that continues to be a significant source of morbidity and mortality around the world. The majority of human illness is caused by Bordetella pertussis, and some is caused by Bordetella parapertussis. Bordetella is a Gram-negative, pleomorphic, aerobic coccobacillus. In the past several years, even countries with high immunization rates in early childhood have experienced rises in pertussis cases. Reasons for the resurgence of reported pertussis may include molecular changes in the organism and increased awareness and diagnostic capabilities, as well as lessened vaccine efficacy and waning immunity. The most morbidity and mortality with pertussis infection is seen in infants too young to benefit from immunization. Severe infection requiring hospitalization, including in an intensive care setting, is mostly seen in those under 3 months of age. As a result, research and public health actions have been aimed at better understanding and reducing the spread of Bordetella pertussis. Studies comparing the cost benefit of cocooning strategies versus immunization of pregnant women have been favorable towards immunizing pregnant women. This strategy is expected to prevent a larger number of pertussis cases, hospitalizations, and deaths in infants <1 year old while also being cost-effective. Studies have demonstrated that the source of infection in infants usually is a family member. Efforts to immunize children and adults, in particular pregnant women, need to remain strong.

Effectiveness of pertussis vaccination and duration of immunity

BACKGROUND

A resurgence of pertussis cases among both vaccinated and unvaccinated people raises questions about vaccine effectiveness over time. Our objective was to study the effectiveness of the pertussis vaccine and characterize the effect of waning immunity and whole-cell vaccine priming.

METHODS

We used the test-negative design, a nested case-control study with test-negative individuals as controls. We constructed multivariable logistic regression models to estimate odds ratios (ORs). Vaccine effectiveness was calculated as (1 - OR) × 100. We assessed waning immunity by calculating the odds of developing pertussis per year since last vaccination and evaluated the relative effectiveness of priming with acellular versus whole-cell vaccine.

RESULTS

Between Dec. 7, 2009, and Mar. 31, 2013, data on 5867 individuals (486 test-positive cases and 5381 test-negative controls) were available for analysis. Adjusted vaccine effectiveness was 80% (95% confidence interval [CI] 71% to 86%) at 15-364 days, 84% (95% CI 77% to 89%) at 1-3 years, 62% (95% CI 42% to 75%) at 4-7 years and 41% (95% CI 0% to 66%) at 8 or more years since last vaccination. We observed waning immunity with the acellular vaccine, with an adjusted OR for pertussis infection of 1.27 (95% CI 1.20 to 1.34) per year since last vaccination. Acellular, versus whole-cell, vaccine priming was associated with an increased odds of pertussis (adjusted OR 2.15, 95% CI 1.30 to 3.57).

INTERPRETATION

We observed high early effectiveness of the pertussis vaccine that rapidly declined as time since last vaccination surpassed 4 years, particularly with acellular vaccine priming. Considering whole-cell vaccine priming and/or boosters in pregnancy to optimize pertussis control may be prudent.

Pertussis prevalence and its determinants among children with persistent cough in urban Uganda

BACKGROUND

We determined prevalence of pertussis infection and its associated host and environmental factors to generate information that would guide strategies for disease control.

METHODS

In a cross-sectional study, 449 children aged 3 months to 12 years with persistent cough lasting ≥14 days were enrolled and evaluated for pertussis using DNA polymerase chain reaction (PCR) and ELISA serology tests.

RESULTS

Pertussis prevalence was 67 (15% (95% Confidence Interval (CI): 12-18)) and 81 (20% (95% CI: 16-24)) by PCR and ELISA, respectively among 449 participating children. The prevalence was highest in children with >59 months of age despite high vaccination coverage of 94% in this age group. Study demographic and clinical characteristics were similar between pertussis and non-pertussis cases. Of the 449 children, 133 (30%) had a coughing household member and 316 (70%) did not. Among 133 children that had a coughing household member, sex of child, sharing bed with a coughing household member and having a coughing individual in the neighborhood were factors associated with pertussis. Children that had shared a bed with a coughing household individual had seven-fold likelihood of having pertussis compared to children that did not (odds ratio (OR) 7.16 (95% CI: 1.24-41.44)). Among the 316 children that did not have a coughing household member, age <23 months, having or contact with a coughing individual in neighborhood, a residence with one room, and having a caretaker with >40 years of age were the factors associated with pertussis. Age <23months was three times more likely to be associated with pertussis compared to age 24-59 months (OR 2.97 (95% CI: 1.07-8.28)).

CONCLUSION

Findings suggest high prevalence of pertussis among children with persistent cough at a health facility and it was marked in children >59 months of age, suggesting the possibility of waning immunity. The factors associated with pertussis varied by presence or absence of a coughing household member.

Combating pertussis resurgence: One booster vaccination schedule does not fit all

Pertussis has reemerged as a major public health concern in many countries where it was once considered well controlled. Although the mechanisms responsible for continued pertussis circulation and resurgence remain elusive and contentious, many countries have nevertheless recommended booster vaccinations, the timing and number of which vary widely. Here, using a stochastic, age-stratified transmission model, we searched for cost-effective booster vaccination strategies using a genetic algorithm. We did so assuming four hypothesized mechanisms underpinning contemporary pertussis epidemiology: (I) insufficient coverage, (II) frequent primary vaccine failure, (III) waning of vaccine-derived protection, and (IV) vaccine "leakiness." For scenarios I-IV, successful booster strategies were identified and varied considerably by mechanism. Especially notable is the inability of booster schedules to alleviate resurgence when vaccines are leaky. Critically, our findings argue that the ultimate effectiveness of vaccine booster schedules will likely depend on correctly pinpointing the causes of resurgence, with misdiagnosis of the problem epidemiologically ineffective and economically costly.

Licensed pertussis vaccines in the United States. History and current state

The United States switched from whole cell to acellular pertussis vaccines in the 1990s following global concerns with the safety of the whole cell vaccines. Despite high levels of acellular pertussis vaccine coverage, the United States and other countries are experiencing large pertussis outbreaks. The aim of this article is to describe the historical context which led to acellular pertussis vaccine development, focusing on vaccines currently licensed in the US, and to review evidence that waning protection following licensed acellular pertussis vaccines have been significant factors in the widespread reappearance of pertussis.

Pertussis Surveillance Trends in British Columbia, Canada, over a 20-year Period: 1993-2013

Objective

To provide a surveillance update on overall and age-related pertussis trends in British Columbia (BC), Canada, spanning the 20-year period from 1993-2013.

Methods

Provincial surveillance data for confirmed pertussis cases were extracted from January 1, 1993 to October 31, 2013. Annual and age-specific incidence rates were derived using provincial and regional population estimates.

Results

BC experienced substantial pertussis epidemics in the late 1990s and early 2000s with incidence ranging from 20 to 40 per 100,000 overall and peaking in pre-teens aged 10-13 years at >200 per 100,000 during the epidemic of 2000. Overall incidence dropped to historical lows ranging from 1 to 6 per 100,000 between 2005 and 2011. This low-level activity was followed by resurgence in 2012 driven by outbreaks in Lower Mainland regions of BC with overall provincial incidence reaching 10 per 100,000. Age-specific incidence in 2012 was highest among infants <1 year old (64 per 100,000) and children 12-13 years old (56-57 per 100,000), with a shift in the age distribution away from preschool-aged children toward pre-teens and young teens evident since 2000. Adult incidence remained <10 per 100,000 throughout the study period and was 5 per 100,000 in 2012. Year-to-date provincial incidence rates overall for 2013 are 6 per 100,000, with ongoing asynchronous activity observed primarily on Vancouver Island.

Conclusions

Pertussis activity in BC showed expected cyclical fluctuations, with a peak incidence observed in 2012, mostly affecting infants and pre-teens/teens but at lower levels than prior peaks. Following substantial epidemics in the 1990s and early 2000s and the incorporation of acellular pertussis vaccine into the routine immunization program, the immuno-epidemiology of pertussis may still be in transition. Further monitoring and evaluation are needed to guide possible program changes for BC.

Are vaccination programs and isolate polymorphism linked to pertussis re-emergence?

Whooping cough remains an endemic disease, and the re-emergence of pertussis in older children and adolescents has been reported in several countries, despite high vaccine coverage. Polymorphism of Bordetella pertussis has been observed over time, and some characteristics of pertussis isolates have gradually diverged from the vaccine strains. The present review summarizes the current knowledge on B. pertussis variability in countries with different vaccination programs and discusses its potential impact on the recently observed increased incidence of whooping cough. No direct association between B. pertussis isolate variability and vaccination programs has been observed to date, except for shifts from fimbriae Fim2 to Fim3. More likely explanations for the re-emergence of pertussis include the change in the epidemiology and transmission patterns of pertussis in highly vaccinated populations, and a shift of disease from young children to adolescents and adults due to waning protective immunity.

Estimation of the underlying burden of pertussis in adolescents and adults in Southern Ontario, Canada

Despite highly successful vaccination programs and high vaccine uptake, both endemic pertussis and periodic pertussis outbreaks continue to occur. The under-recognized role of adolescents and adults in disease transmission, due to waning immunity following natural infection and vaccination, and reduced likelihood of correct diagnosis, may contribute to pertussis persistence. We constructed a mathematical model to describe the transmission of pertussis in Southern Ontario in both pre-vaccine and vaccine eras, to estimate the underlying burden of pertussis in the population. The model was well calibrated using the best available data on pertussis in the pre-vaccination (1880–1929) and vaccination (1993–2004) eras in Ontario. Pertussis under-reporting by age group was estimated by comparing model-projected incidence to reported laboratory-confirmed cases for Greater Toronto. Best-fit model estimates gave a basic reproductive number of approximately 10.6, (seasonal range 9.9 to 11.5). Under-reporting increased with age, and approximately >95% of infections in children were caused by infections in persons with waning immunity to pertussis following prior infection or vaccination. A well-calibrated model suggests that under-recognized cases of pertussis in older individuals are likely to be an important driver of ongoing pertussis outbreaks in children. Model projections strongly support enhancement of booster vaccination efforts in adults.

Genetic analysis of Bordetella pertussis in Ontario, Canada reveals one predominant clone

OBJECTIVE

To characterize Bordetella pertussis isolates in Ontario, Canada in order to understand the clonal diversity of strains present in this province.

METHODS

A total of 521 isolates from the period 1998-2006 were analyzed by serotyping, pulsed-field gel electrophoresis (PFGE), and DNA sequencing of their virulence factors of pertactin, fimbriae 3, pertussis toxin subunit 1, and pertussis toxin gene promoter. Characteristics of the Ontario isolates were compared to those described for isolates from Europe and Australia.

RESULTS

A single predominant clone was identified in Ontario, Canada, represented by 83.5% of the 521 isolates analyzed. This clone was characterized by the genotype fim3B, prn2, ptxS1A, and ptxP3 (sequence type (ST)-1), and 72.9% of this clone displayed three closely related PFGE profiles of BpSR11, BpSR5, and BpSR12. Pertussis isolates in Europe with these PFGE profiles and virulence factor genotype are reported as common. The Australian epidemic clone was previously reported to have the genotype prn2 and ptxP3.

CONCLUSION

The finding of one predominant B. pertussis clone in Ontario, Canada, with characteristics identical to strains involved in epidemics in Europe and Australia, suggests a potential link of this strain to the resurgence of pertussis in this province.

Infants hospitalised with pertussis: estimating the true disease burden

AIM

New Zealand (NZ) has a large pertussis disease burden compared with other developed countries. Accurate ascertainment of disease burden is fundamental to controlling pertussis and informing immunisation policy. Disease burden estimates are primarily from passive surveillance, which underestimates disease incidence. The aim of this study is to use active surveillance to determine pertussis disease burden in infants hospitalised in NZ.

METHODS

Using the NZ Paediatric Surveillance Unit, active surveillance from 08/2004 to 07/2005 for infants <12 months old, hospitalised with pertussis.

RESULTS

110 infants identified (196 per 100,000), including six with complications, eight intensive care admissions and one death. The hospitalisation rate (per 100,000) varied with ethnicity, being higher for Maori (296) and Pacific (358) compared with European/other (117). Twenty-four per cent were too young to be immunised. Of infants 6 weeks and older 46% had received no immunisations. Despite being more likely to be immunised Pacific infants had a higher hospitalisation rate owing to a larger proportion acquiring pertussis prior to age 6 weeks. Cyanosis and apnoea were frequent symptoms in young infants. Under-identification, estimated using capture-recapture analysis, was modest for both active surveillance (16%) and passive notification (19%).

CONCLUSIONS

Infant pertussis hospitalisation rates are three to six times greater than rates in the USA, England and Australia. Underestimation of disease burden by passive notification in hospitalised infants is modest, suggesting a high degree of clinical awareness by paediatricians in NZ. New immunisation strategies are needed to protect infants from a younger age.

Hospitalisations due to pertussis in New Zealand in the pre-immunisation and mass immunisation eras

AIM

Pertussis disease burden in New Zealand in recent decades has been large compared with other developed countries. However, these comparisons use data from relatively short time periods given the long epidemic cycle of pertussis. To better understand the current disease burden, this study examined pertussis hospitalisation data in New Zealand in both the pre-immunisation and mass immunisation eras.

METHODS

Hospital discharge data and population data from 1873 to 2004 were used to estimate average pertussis hospital discharge rates per decade. Rates were compared using relative risks and 95% confidence intervals (CI).

RESULTS

Average annual pertussis hospitalisation rates per 100000 were less than two from 1873 to 1919, increased to 12 in the 1940s, decreased to less than four in the 1960s and have increased since then with the rate in the current decade being 5.8. Compared with the 1960s (3.8 per 100000) the average annual rate has been significantly greater in the 1980s (RR=1.11, 95% CI 1.03, 1.21), 1990 s (RR=1.33, 95% CI 1.23, 1.44) and 2000s (RR=1.55, 95% CI 1.42, 1.68). Since 1960 hospitalisation rates have increased for those less than one year old, one to four years old and five years and older. The increases have been most marked for infants (RR 2000s vs. 1960s=2.87, 95% CI 2.59, 3.18).

CONCLUSION

After an initial decline following mass immunisation, pertussis hospitalisation rates in New Zealand have subsequently increased steadily. To reduce pertussis disease burden improved immunisation coverage and timeliness is required and consideration given to spreading the pertussis vaccine schedule over a wider age range.

The effect of changing from whole-cell to acellular pertussis vaccine on the epidemiology of hospitalized children with pertussis in Canada

BACKGROUND

Between July 1997 and April 1998, universal childhood immunization programs in Canada changed from using a whole-cell pertussis to a 5-component acellular pertussis-containing vaccine. To assess effects on pertussis epidemiology of this nationwide change, we analyzed hospitalizations during 1991-2004 using the Canadian Immunization Monitoring Program, Active (IMPACT) pertussis database.

METHODS

IMPACT is an active surveillance network based in 12 pediatric tertiary-care hospitals across Canada. Characteristics of hospitalized cases of pertussis were compared by type of vaccine received or by birth date (if immunization records were unavailable or the child was unvaccinated). Age-stratified incidence rates were calculated by year and vaccine type.

RESULTS

Two thousand ninety-six cases of pertussis were admitted to IMPACT centers, 1174 during the whole-cell vaccine program (WCV-P) and 842 during the acellular vaccine program (ACV-P). Pertussis incidence among children <5 years old decreased significantly during the ACV-P, causing an increase in the residual proportion of cases either too young to be immunized (<2 months old: ACV-P 39% versus WCV-P 26.1%; P < 0.0001) or too young for a second dose (2-3 months old: 42.9% versus 34.2%, respectively; P < 0.0001). A significantly smaller proportion of cases (ACV-P 15.1% versus WCV-P 27.3%) occurred in infants who were old enough (4-11 months of age) to have received 2 or 3 doses of vaccine.

CONCLUSIONS

With ACV-P, pertussis hospitalizations in children 4-59 months old decreased in frequency, consistent with improved vaccine effectiveness, but remained prominent among very young infants. Improved control strategies are needed to reduce infections among infants too young for pertussis vaccination.

[Measles, pertussis, rubella and mumps completeness of reporting. Literature review of estimates for industrialized countries]

BACKGROUND

Surveillance data for infectious diseases in industrialized countries have been providing useful epidemiological information for several years. However, surveillance is complex and notifications underestimate the true disease incidence. The goal of this paper is to determine the completeness of reporting of measles, pertussis, rubella and mumps through notification in industrialized countries.

METHODS

A thorough literature review of papers published (in French or English) on surveillance data of measles, pertussis, rubella and mumps was undertaken with PUBMED. The review was limited to studies conducted in industrialized countries that quantitatively assessed the completeness of the reporting of these diseases.

RESULTS

Fourteen studies published from the 1920s met the inclusion criteria. For measles, the studies suggest that 64-85% of symptomatic patients sought medical care, 13-57% of those were diagnosed with measles and 22-81% of the diagnosed cases were reported for a completeness of reporting ranging from 7% to 63% between 1920 and 1980 and 3% to 41% in recent years. For pertussis, it was estimated that 49-59% of symptomatic patients sought medical care, 12% of those were diagnosed and 19-47% of the diagnosed cases were reported for a completeness of reporting ranging from 5% to 25% between 1920 and 1980 and from 3% to 12% in recent years. Very few studies on rubella and mumps were found and none allowed the determination of the global completeness of reporting.

CONCLUSION

Reporting has been found to be considerably incomplete. Continued efforts to improve the recognition and reporting of these diseases are needed.

Economic evaluation of an extended acellular pertussis vaccine program for adolescents in Québec, Canada

OBJECTIVE

Pertussis is a frequent cause of cough illness in adolescents. In Canada, immunization against pertussis in public programs has been restricted to children under 7 years of age. The purpose of this analysis was to estimate the health and economic impact of an additional booster dose of the acellular vaccine in adolescents in Québec.

METHOD

We performed a cost-effectiveness analysis, based on a predictive spreadsheet dynamic model following a cohort of 90,929 adolescents in Québec from the age of 14 years over a 10-year period from the Québec Ministry of Health (MOH) and societal (SOC) perspectives. The model was used to compare costs (2003 values) and benefits of an adolescent vaccination program (AVP), including a diptheria, tetanus, and acellular pertussis (dTacp) vaccine administered at age 14 years, with current practice.

RESULTS

From the MOH perspective, a booster vaccination of dTacp at age 14 years via the AVP would produce a yearly additional expected cost of Can dollars 1.06 per adolescent with an incremental cost-effectiveness ratio (ICER) of Can dollars 480 per pertussis case avoided based on a 10-year period. When outcomes are discounted at 3%, the ICER rises to Can dollars 527 per discounted pertussis case avoided. From the SOC perspective, the AVP would cost Can dollars 0.83 per adolescent per year with an additional cost per avoided pertussis case of Can dollars 377 (Can dollars 414 per additional discounted case of pertussis avoided). Over the 10-year period, 2012 non-discounted cases of pertussis would be prevented with approximately two hospital admissions averted.

CONCLUSION

This study suggests that administering a booster dose of dTacp at age 14 years to replace the diptheria and tetanus vaccination will slightly increase the economic burden from MOH and SOC perspectives; however, the number of pertussis cases and the number of hospital admissions will decrease.

Epidemiological characteristics of pertussis in Vojvodina

Introduction. In the preimmunization era, pertussis was one of the most common respiratory diseases in children in Vojvodina. Material and methods. This paper deals with effects of immunization against pertussis in Vojvodina and its epidemiological characteristics during the last 10 years. Results and discussion. The average incidence rate for the preimmunization era (1948-1960) was 122/100.000. During the period of immunization, the incidence rate has been continuously declining. During the period from 1995 till 2004, average incidence rate was 0,2/100.000 There were 125 registered deaths caused by pertussis in the preimmunization era, and 13 deaths in the immunization period. The last case of death caused by pertussis occurred in 1970. Pertussis vaccination coverage in Vojvodina has been above 95% for a long period of time. Pertussis is still reported, mostly in individual cases. Since 2003, it was registered in children younger than 24 months. During the last decade, 82% of cases were unimmunized children. The majority of affected were infants (59%) and children from 12 to 24 months of age (15%). Pertussis is registered in small children due to delayed immunization and in school children due to loss of immunity. Conclusion. Favorable epidemiological situation of pertussis in Vojvodina is the result of high immunization coverage. The disease is most frequently registered in individual cases, in unimmunized infants and small children. Mild cases of pertussis remain unrecognized in older age groups, in previously immunized children. It is necessary to improve surveillance and laboratory diagnostics of pertussis in order to monitor the epidemiological situation and to provide timely investigation and control of pertussis. .

Economic evaluation of an extended acellular pertussis vaccine programme for adolescents in Ontario, Canada

PURPOSE

Pertussis is a frequent cause of cough illness in adolescents. In Canada, until recently immunization against pertussis in public programmes has been restricted to children under the age of 7. The purpose of this analysis was to estimate the health and economic impact of an additional booster dose of the acellular vaccine in adolescents in Ontario.

METHODS

We performed a cost effectiveness analysis, based on a predictive spreadsheet dynamic model following a cohort of 144,000 adolescents in Ontario from the age of 12 years over a 10-year-period from the Ontario Ministry of Health (MoH) and societal perspectives. The model was used to compare costs and benefits of a combined vaccination programme (CVP) including tetanus, diphtheria, and acellular pertussis (dTacp) administered at age 12, compared to current practice.

RESULTS

From the MoH perspective, booster vaccination of dacpT at 12 years via the CVP would produce a yearly additional expected cost of CAD $0.52 per adolescent in Ontario with an incremental cost-effectiveness ratio of CAD $168 per pertussis case avoided based on a 10-year-period. If outcomes are discounted at 3%, the incremental cost-effectiveness ratio rises to $188/discounted pertussis case avoided. From the societal perspective, the CVP would be cost saving CAD $858,106 at 10 years for the cohort. Over the 10-year-period, more than 4400 cases of pertussis would be prevented with approximately 50 hospital admissions averted.

CONCLUSIONS

This study suggests that administering a booster dose of dTacp at 12 years of age to replace diphtheria and tetanus vaccination at 14 years may reduce the economic burden of pertussis treatment in the long term at a reasonable cost.

Polymorphisms of the fimbria fim3 gene of Bordetella pertussis strains isolated in Canada

The fim genes which code for the fimbria protective antigens present in both the inactivated whole-cell and acellular vaccines were analyzed in 86 Canadian Bordetella pertussis isolates. At least one of the novel mutations identified was found to involve a surface epitope that has been mapped by serum antibodies from infected or vaccinated subjects.

Use of birth certificates and surveillance data to characterize reported pertussis among Texas infants and young children, 1995 to 2000

BACKGROUND

Pertussis morbidity is increasing, especially among young infants and children, who are more likely to be hospitalized and have more severe complications. Maternal and pediatric factors associated with underimmunization and hospitalization for pertussis are poorly understood, but young maternal age and low birth weight have been associated with pertussis among young infants.

METHODS

We used pertussis surveillance data, matching cases to the birth certificates of 416 Texas infants and children reported as pertussis cases during 1995 to 2000. Maternal/pediatric information gathered from birth certificates included birth weight, gestational age, and maternal factors (age, birthplace and education level, prenatal care, and previous live births). We assessed the immunization status of the cases and maternal/pediatric factors associated with underimmunization with a pertussis-containing vaccine and hospitalization using descriptive statistics and logistic regression.

RESULTS

The 416 cases represented 20% of the pertussis morbidity in Texas from 1995 through 2000. Most children had not been vaccinated (275 [66%]), even though 374 (90%) were old enough for at least one dose. Among those 374 children, only those younger than 6 months were associated with underimmunization (odds ratio [OR], 9.98; 95% confidence interval [CI], 6.24-15.97). Most patients (253 [61%]) were hospitalized. Hospitalization was associated with complications of apnea (OR, 2.13; 95% CI, 1.39 2.38), pneumonia (OR, 5.26; 95% CI, 2.94-11.59), and age younger than 6 months (OR, 2.11; 95% CI, 1.38-3.23).

CONCLUSION

More than two-thirds of the children reported as pertussis cases were old enough to have at least one dose of a pertussis-containing vaccine but were not immunized. Maternal and pediatric characteristics on birth certificates were not useful in predicting either underimmunization or hospitalization for pertussis complications. More current assessments of maternal and pediatric characteristics should be part of pertussis contact investigations.

Injection-site reactions to booster doses of acellular pertussis vaccine: rate, severity, and anticipated impact

BACKGROUND

Acellular pertussis (aP)-containing vaccines cause fewer adverse events than whole-cell versions for primary doses. Booster doses, however, may be followed by extensive injection-site reactions. This study compares the frequency, severity, and impact of local reactions among children receiving 5 consecutive doses of an aP combination vaccine (including inactivated polio virus, conjugated Haemophilus influenzae type b antigen, and diphtheria and tetanus toxoids) to children receiving a mixed series of whole-cell and aP combination vaccines.

METHODS

Participants were parents or guardians of children 4 to 6 years old immunized at public health clinics across British Columbia, Canada. This included 398 children receiving the fifth consecutive dose of an aP combination vaccine and 402 receiving the fifth dose in a mixed series consisting of at least 1 prior dose of whole-cell pertussis combination vaccine with the remainder as aP combination vaccine. A cross-sectional telephone survey evaluated the extent of local reactions 48 to 96 hours after immunization by asking participants to compare the size of redness and swelling with familiar household items such as Oreo cookies or coins. Associated discomfort and impact on recreational activities, health care utilization, parental time off work, and attitudes toward immunization were also assessed.

RESULTS

Children who received the fifth consecutive dose of an aP combination vaccine more often experienced redness (24%) or swelling (16%) the size of an Oreo cookie or larger (>or=46 mm) than children given a mixed series (10% and 9%, respectively) but less often experienced tenderness or limitation of movement at the injection site. Related health care utilization was low. There was no discernible effect on participation in recreational activities or parental attitudes toward vaccine; 90% would recommend the same vaccine to others with children of the same age.

CONCLUSIONS

We conclude that injection-site reactions are more extensive after the fifth consecutive dose of an aP combination vaccine compared with the fifth dose in a mixed series of whole-cell and aP combination vaccines. These reactions are unlikely to affect parental acceptance of immunization recommendations or health care utilization.

Effect of the preschool pertussis booster on national notifications of disease in Australia

BACKGROUND

Australia introduced a fifth dose of pertussis vaccine at 4 to 5 years of age in 1994, the first country to do so for some 40 years. We report trends in national pertussis notifications from 1993 to 2001.

METHODS

Notified pertussis cases were analyzed by age and year of disease onset.

RESULTS

Before the fifth dose was introduced, notification rates were higher among 5- to 9-year-olds than 10- to 14-year-olds (76 per 100 000 population vs.65 per 100 000). As more 5- to 9-year-olds became eligible for the fifth dose, their notification rates as a group and by year of age progressively fell to below those of 10- to 14-year-olds, consistent with a vaccine effect. Comparison of notification rates for the epidemic years of 1997 and 2001 shows that 5- to 10-year-olds (eligible for fifth dose) had lower notification rates in 2001 (61 per 100 000) than 5- to 10-year-olds in 1997 (196 per 100 000). This contrasts with children who were not eligible for the fifth dose (12- to 14-year-olds), who had higher notification rates in 2001 (223 per 100 000) than 12- to 14-year-olds in 1997 (160 per 100 000).

CONCLUSIONS

The pattern of age-specific notification rates provides strong evidence that the fifth dose reduced the incidence of pertussis in older children. It will be important to track the impact of the fifth dose on adolescent pertussis notifications to assess the duration of vaccine-acquired immunity.

Effects of pertussis vaccination on disease: vaccine efficacy in reducing clinical severity

We estimated the effectiveness of pertussis vaccination in reducing the clinical severity of breakthrough disease among vaccinated individuals from a comprehensive follow-up study of a community of 30,000 residents of Niakhar, Senegal, in 1993. A physician examined all children with potential pertussis (cough of >7 days' duration). Samples were collected from 97% of these children for culture or serologic testing as part of the active surveillance for a pertussis vaccine trial. Cases of pertussis were defined by confirmation through culture or serologic testing or by a history of contact with a person with culture-confirmed pertussis. Among children with confirmed cases, severity of illness was assessed according to a scale that combined clinical signs and symptoms. The efficacy of the vaccine in reducing disease severity was 48% (95% confidence interval, 39%-55%) among children vaccinated with 3 doses of whole-cell (67%) or acellular (32%) vaccine. Primary cases were more severe than secondary cases in residential compounds. Pertussis vaccination is effective in reducing the severity of illness.

How best to estimate the global burden of pertussis?

In most countries, pertussis surveillance is inadequate for accurately estimating numbers of cases or deaths. Good estimates are needed to help set priorities for vaccination programmes. We aimed to develop a simple, reliable, and explicit method for estimating pertussis cases and deaths for children under 15 years to calculate the global disease burden in 1999. We estimated the proportion of susceptible children becoming infected in countries with poor vaccination coverage (<70%) in 1999 at 30% by 1 year, 80% by 5 years, and 100% by 15 years of age and for countries with good coverage (> or =70%) at 10% by 1 year, 60% by 5 years, and 100% by 15 years. Vaccine efficacy was estimated at 80% for preventing infection and 95% for preventing deaths. We used UN population estimates and vaccination coverage reported to WHO (adjusted for specific survey data if available). Case fatality ratios for countries with high and low child mortality were derived from published and unpublished work. For some countries with good vital events registration we used reported deaths adjusted for underascertainment. In 1999 there were an estimated 48.5 million pertussis cases in children worldwide. Deaths from pertussis were estimated at 390000 and at 295000 after adjustment for local data sources. Based on this approach, disability-adjusted life years from pertussis (12.7 million) in 2000 exceeded those of other preventable diseases such as lung cancer (11.4 million) and meningitis (5.8 million). This simple approach yields estimates that can be used for setting vaccination programme priorities. Better data are needed on the public health importance of pertussis in high mortality countries, the benefits of incomplete vaccination, and the harm from delayed vaccination.

Pertussis resurgence in Canada largely caused by a cohort effect

BACKGROUND

Beginning in 1990 Canada experienced a resurgence of pertussis. Changes in incidence and hospitalization according to age in the province of Quebec between 1983 and 1998 were examined to assess the presence of a cohort effect resulting from a poorly protective vaccine.

METHODS

The source of data on incident cases was pertussis notifications to the Quebec Ministry of Health and Social Services. Hospitalization data were extracted from the administrative database that collects information on each hospitalization.

RESULTS

The mean annual incidence before 1990 was 3.8 cases per 100,000 population which increased to 37.2 thereafter. Infants had the smallest increase (2.7-fold) when compared with children between 1 and 19 years who experienced a 9- to 15-fold increase and with adults (22.5-fold). The mean annual hospitalization rates increased from 2.7 per 100,000 before 1990 to 5.2 afterward. Ninety percent of hospitalizations occurred in children <5 years of age. The proportion of cases in 0- to 4-year-old children decreased, whereas it increased steadily in all other age groups during the entire study period. Between 1990 and 1998 the median age of cases shifted from 4.4 to 7.8 years. Pertussis affected predominantly children who were immunized with a vaccine introduced in the mid-1980s. The evolution of the age distribution of cases paralleled the aging of this cohort with a slow but steady drift of disease from early childhood to adolescence.

CONCLUSION

The sudden increase in pertussis incidence in Canada can be largely attributed to a cohort effect resulting from a poorly protective pertussis vaccine used between 1985 and 1998.

Which strategy for pertussis vaccination today?

Pertussis (whooping cough) remains an epidemic disease responsible for infant and child morbidity and mortality, and is perceived as a serious public health problem. Since the widespread use of whole-cell pertussis vaccines in the 1940s, vaccination programs have varied greatly between countries. National specificity is a function of several factors. The most important are: vaccine efficacy and tolerability;vaccine coverage and distribution; and vaccine acceptance by parents and professionals. During the 1970s, Sweden, England, Wales and Japan provided contrasting examples of the attitude of health authorities to the use of whole-cell vaccines. The increase in pertussis incidence was noted as a consequence of active opposition to this vaccine. The re-emergence of pertussis in the 1990s, in countries with high vaccination coverage and increased incidence of disease in individuals >15 years and <6 months of age, has drawn attention to the role of booster doses of pertussis vaccines and their introduction into regular vaccination programs. The use of acellular vaccines for booster doses for adolescents and adults would seem unambiguous because of their decreased reactogenicity, although the exact schedule has yet to be established. The choice between the two kinds of vaccines is more difficult for primary courses, where safety and efficacy profiles are similar, and the attitude towards acellular vaccines varies from country to country. In this case, the strategy adopted results from the national history of pertussis infection and from the quality of the available whole-cell vaccine. Two contrasting examples are the US, where acellular vaccines were licensed for the primary series in the 1990s, and the UK, where whole-cell vaccines are exclusively used for primary immunization. The changing epidemiology of pertussis, and its local diversification, would suggest that at present it is difficult to define a single worldwide strategy with only one kind of vaccine and one schedule. In order to control pertussis incidence, each country should continue to determine the best national vaccination program established in very close relation to the past and present epidemiological situation and available healthcare resources.

Effectiveness of a single dose of acellular pertussis vaccine to prevent pertussis in children primed with pertussis whole cell vaccine

We estimated the protection given by one booster dose of acellular pertussis vaccine (aP) given at 18 months or before school entry to children already primed with whole cell vaccine (wP). Case-control studies were conducted in these two age groups. In children who received or were eligible to receive their 18 months booster, the risk of pertussis was 1.4 and 3.6 times higher for those with 4 and 3 wP, respectively, compared to those with 3 wP + 1 aP. In 5 and 6 yr old children, the risk of pertussis among the subjects with 5 and 4 wP, was 1.4 and 2.1 times higher respectively than in those who received 4 wP + 1 aP. A single dose of aP increased the protection against pertussis and this protection was greater than that obtained with a wP booster.

Detection of Bordetella pertussis in a clinical laboratory by culture, polymerase chain reaction, and direct fluorescent antibody staining; accuracy, and cost

Control of Bordetella pertussis in the community is hampered by slow and insensitive diagnostic tests. We therefore examined the accuracy and cost of culture, direct fluorescent antibody (DFA) staining, and PCR in a routine clinical laboratory. Six hundred thirty seven nasopharyngeal swabs and aspirates in casamino acids transport medium were cultured, stained with polyclonal (Difco), and monoclonal (BL-5 and Accu-Mab) anti-B. pertussis reagents, and amplified by an IS481-specific PCR. PCR products were detected by a hybridization-enzyme immunoassay kit (Gen-eti-k DEIA, DiaSorin), with confirmation by a second PCR in a separate laboratory. Sensitivities and specificities of culture, polyclonal DFA, monoclonal DFA, and PCR were 36 and 100%, 11.4 and 94.6%, 8.3 and 98. 4%, and 95.0 and 99.3%, respectively, with a prevalence of 15.7%. The DFA tests were the most economical, and the PCR cost was 31% higher than culture. This study suggests that with minor improvements in economy, pertussis PCR can be implemented in a clinical laboratory with marked improvement in diagnostic accuracy.

A randomized, placebo-controlled trial of erythromycin estolate chemoprophylaxis for household contacts of children with culture-positive bordetella pertussis infection

CONTEXT

Household contacts of patients with pertussis are at increased risk of acquiring infection. Chemoprophylaxis has been recommended to decrease transmission, particularly to young infants who are at increased risk of severe disease. Although epidemiologic investigations of outbreaks have suggested a benefit, there have been no prospective studies evaluating the efficacy of chemoprophylaxis in preventing secondary cases of pertussis.

OBJECTIVE

To determine whether erythromycin estolate chemoprophylaxis is effective in household contacts of children with culture-positive pertussis.

DESIGN

Randomized, double-blind, placebo-controlled study.

SETTING

Community based.

SUBJECTS

All household contacts of 152 children with culture-positive pertussis who provided consent (n = 362). After withdrawals, there were 135 households with 310 contacts. Exclusions included pregnancy, age <6 months, already receiving an erythromycin-containing antibiotic, and erythromycin allergy. INTERVENTUINS: Erythromycin estolate (40 mg/kg/day in 3 divided doses; maximum dose 1 g) or placebo for 10 days. Nasopharyngeal cultures, pertussis antibodies, and clinical symptoms were assessed before and after treatment.

PRIMARY OUTCOME

Measure efficacy of erythromycin estolate chemoprophylaxis calculated by the proportion of households in each group with a member who developed a nasopharyngeal culture positive for Bordetella pertussis.

RESULTS

There was no difference in the development of respiratory tract symptoms compatible with a case definition of pertussis in the erythromycin- and placebo-treated groups. There were 20 households with secondary culture-positive cases of pertussis; 4 households in the erythromycin-treated group and 15 in the placebo-treated group (efficacy of erythromycin chemoprophylaxis for bacterial eradication 67.5% [95% confidence interval: 7.6-88.7]). However, medication-associated adverse reactions were reported by 34.0% of erythromycin and 15.7% of placebo recipients.

CONCLUSIONS

Under the conditions of this study, erythromycin estolate prevented culture-positive pertussis in household contacts of patients with pertussis but did not prevent clinical pertussis.

Clinical manifestations of Bordetella pertussis infection in immunized children and young adults

STUDY OBJECTIVES

The incidence and prevalence of pertussis in adults have increased in recent years. It has been shown that previously immunized adults and adolescents are the main sources of transmission of Bordetella pertussis. The aim of this study was to describe the clinical presentation and the clinical course of pertussis in children and young adults who were immunized previously against B pertussis.

DESIGN

Retrospective study.

SUBJECTS

Children and young adults who were reported by local physicians to the Department of Epidemiology in the Israeli Ministry of Health with serologically confirmed pertussis and who were immunized previously were included. Information sought included personal data, epidemiologic data, signs and symptoms, laboratory results, initial diagnosis, and treatment.

RESULTS

In the 95 previously immunized patients with serologically confirmed pertussis (mean age [+/- SD], 8.9 +/- 4.4 years old; range, 5 to 30 years old), the mean duration from onset of symptoms until the final diagnosis of pertussis was 23 +/- 15 days. The disease was usually atypical and generally mild. All the described patients had cough, usually prolonged, lasting 4 +/- 3.6 weeks. Only 6% had the classic whoop. The mean WBC count was 8.7 +/- 2.6 cells/mm6, and the lymphocyte count was 40 +/- 12%. Two patients were admitted to the hospital for severe pneumonia. Among the reported cases, the proportion of patients between the ages of 10 and 45 years increased from 6.5% during the period from 1971 to 1980, to 26% during the period from 1980 to 1990, and to 38% during a 1989 outbreak.

CONCLUSIONS

Pertussis in previously immunized individuals is usually characterized by an atypical and relatively mild clinical course. Patients suffer mainly from a prolonged and persistent cough. Early diagnosis may lead to prompt administration of therapy. Prophylaxis of exposed persons might be effective in decreasing both severity and transmission of the disease.

A single dose of an effective whole cell pertussis vaccine does not significantly increase protection in children primed with a less effective vaccine

We evaluated if a single dose of a protective whole cell pertussis vaccine given before school entry to children primed with a less effective vaccine would increase their protection. A school cohort including 3876 students and a family cohort including 162 children were assessed. Although there was a trend toward increased protection. the better vaccine did not provide a significant improvement. These results suggest that a single dose of an effective vaccine given to children primed with a less effective one does not raise the protection to at level similar to that provided by three doses of the better vaccine.

Epidemiology of pertussis in French hospitals in 1993 and 1994: thirty years after a routine use of vaccination

BACKGROUND

Despite widespread vaccination during 30 years, the hypothesis of a resurgence of pertussis in France has been raised by outbreaks and sporadic case reports. No surveillance data were available after 1985.

METHODS

A survey was undertaken in 1993 and 1994 in a pediatric hospital network able to confirm cases; the network (22 hospitals) represents 19.6% of pediatric admissions in France. Case definition included clinical (> or = 21 days of paroxysmal cough), laboratory-confirmed (culture or serology by immunoblot) or epidemiologically confirmed pertussis (documented contact with a laboratory-confirmed case). The pattern of transmission was studied in the household. Vaccine status was obtained from health records.

RESULTS

during a 15-month period 560 cases (316 index cases, 244 household contact cases) were reported; 49% of index cases and 20% of contact cases were confirmed by culture and/or serology. Sixty-five percent of index cases were younger than 1 year of age (the incidence in this age group could be estimated to be 95/100000) and 66% were hospitalized for a mean duration of 2 weeks. Infection was acquired from parents (34%) and siblings (46%). Seventy-three percent of index cases were unvaccinated.

CONCLUSIONS

Although pertussis vaccination coverage is very high in France, the organism is still circulating, affecting, within the pediatric population, mostly non- or incompletely vaccinated infants. These results strongly support the importance of adhering to the immunization schedule and suggest introducing booster dose(s) to prolong vaccine immunity and reduce the exposure to Bordetella pertussis of infants too young to be immunized.

Impact of anti-vaccine movements on pertussis control: the untold story

To assess the impact of anti-vaccine movements that targeted pertussis whole-cell vaccines, we compared pertussis incidence in countries where high coverage with diphtheria-tetanus-pertussis vaccines (DTP) was maintained (Hungary, the former East Germany, Poland, and the USA) with countries where immunisation was disrupted by anti-vaccine movements (Sweden, Japan, UK, The Russian Federation, Ireland, Italy, the former West Germany, and Australia). Pertussis incidence was 10 to 100 times lower in countries where high vaccine coverage was maintained than in countries where immunisation programs were compromised by anti-vaccine movements. Comparisons of neighbouring countries with high and low vaccine coverage further underscore the efficacy of these vaccines. Given the safety and cost-effectiveness of whole-cell pertussis vaccines, our study shows that, far from being obsolete, these vaccines continue to have an important role in global immunisation.

Clinical findings in Bordetella pertussis infections: results of a prospective multicenter surveillance study

OBJECTIVE

To study the clinical presentation of culture-confirmed pertussis in children and their contacts with cough illnesses in an outpatient setting.

METHODOLOGY

In conjunction with a large pertussis vaccine efficacy trial in Germany, a central laboratory to isolate Bordetella species from nasopharyngeal specimens was established in Erlangen in October 1990. Pediatricians in private practices in southern Germany, the Saar region, and Berlin were encouraged to obtain nasopharyngeal specimens and clinical characteristics from patients with cough illnesses >/=7 days' duration. Bordetella species were isolated by use of calcium alginate swabs, Regan-Lowe agar, and modified Stainer-Scholte broth. Clinical characteristics were determined by initial and follow-up questionnaires.

RESULTS

From October 1990 to September 1996, 20 972 specimens were submitted, and B pertussis was isolated in 2592 instances (12.4%). Of the culture-proven cases, 50.7% were female, and the age range was 6 days to 41 years, with a mean and median of 4.3 years and 4.1 years, respectively. The following characteristics were noted. Only 4% of the patients had received pertussis vaccine. Of unvaccinated patients, 90.2% had paroxysmal cough, 78.9% demonstrated whooping, and 53.3% presented with posttussive vomiting; 5.7% had fever >/=38 degrees C. The duration of cough was </=4 weeks in 37.9% and </=3 weeks in 17.4%. Leukocytosis and lymphocytosis (values above the age-specific mean) were observed in 71.9% and 75.9% of unvaccinated patients, respectively. The overall complication rate was 5.8%, and pneumonia (29%) was the most frequent complication. In infants <6 months of age, the rate of complications was 23.8%. One death in a 7-month-old infant occurred.

CONCLUSIONS

Typical symptoms of pertussis were observed in the great majority of patients regardless of age group. However, the duration of cough was surprisingly short in one sixth of the patients. These short illness cases would not be classified as pertussis according to the World Health Organization clinical case definition, which requires >/=21 days of spasmodic cough.

A nasal whole-cell pertussis vaccine can induce strong systemic and mucosal antibody responses which are not enhanced by cholera toxin

The immunogenicity of formaldehyde-inactivated Bordetella pertussis (Bp) delivered by the intranasal or colonic-rectal routes in BALB/c mice was studied by immunization four times at weekly intervals with Bp alone, or with Bp mixed with cholera toxin (CT) as a mucosal adjuvant. Mice given Bp subcutaneously, and untreated mice served as controls. Antibody responses in serum, saliva, bronchoalveolar lavage (BAL) fluids and extracts of faeces were measured by enzyme-linked immunosorbent assay. Nasal immunizations with Bp alone induced high levels of IgG antibodies to Bp in serum and BAL fluids, as well as IgA antibodies in serum, saliva, BAL fluids and extracts of faeces. The IgA responses were significantly reduced, and the IgG responses were not increased, when CT was given intranasally together with Bp. However, CT increased the IgA responses to Bp in faeces when both antigens were given rectally, while rectal administration of Bp alone did not induce significant serum or secretory antibody responses. However, when mixed with Bp, the CT itself induced antibodies to CT in serum and samples representing secretions after both nasal and rectal administrations. Thus, Bp is strongly immunogenic when applied intranasally, but not when presented into the intestinal lumen via the rectal route. It appears that CT, which is known to be a mucosal adjuvant and which in itself is a strong mucosal immunogen, will inhibit the immune responses of other strong immunogens when applied on the nasal mucosa.

Seven days of erythromycin estolate is as effective as fourteen days for the treatment of Bordetella pertussis infections

OBJECTIVE AND METHODS

Although 14 days of erythromycin is recommended for the treatment of Bordetella pertussis infection, there have been no prospective controlled studies to support the contention that this long course of therapy is required to eradicate the microorganism from the nasopharynx or to prevent bacteriological relapse. We randomly allocated children and adults with culture-positive community-acquired pertussis to either 7 or 14 days of erythromycin estolate treatment (40 mg/kg/d; maximum dose 1 g/d). Nasopharyngeal aspirate cultures were obtained by study nurses during home visits before and at the end of treatment, and 1 week after the completion of treatment. B pertussis-specific antibodies were measured before treatment and 1 month later. Information about clinical symptoms, adverse reactions, and compliance were collected at each scheduled contact.

RESULTS AND CONCLUSIONS

A total of 168 participants were eligible for analysis (74 treated for 7 days and 94 treated for 14 days). Bacteriological persistence (positive end of therapy culture) occurred once in each group, and bacteriological relapse (positive culture 1 week after completion of treatment) occurred in one participant treated for 7 days. The overall failure rate (persistence plus relapse) of 2.70% in the 7-day group was not different than the rate of 1.06% in the 14-day group. The study had a power of 99.99% at the 5% level to detect a difference in failure rates of 10% and a power of 80% to detect a difference of 5%. We conclude that 7 days of erythromycin estolate is as effective as 14 days for the eradication of B pertussis.

Estimates of the effectiveness of a whole-cell pertussis vaccine from an outbreak in an immunized population

Pertussis has re-emerged as a public health problem in Canada in recent years, emphasizing concerns about the effectiveness of the currently licensed whole-cell vaccine. Following a 1994 outbreak in Nova Scotia, we conducted a case-control study of 483 children aged < 10 years to assess vaccine effectiveness. Ninety-three percent of children aged 6 months and above had received three or more doses of vaccine, however, only 78% had received age-appropriate immunization. Among children aged 4 years and more, vaccine effectiveness against laboratory-confirmed pertussis was 57% (95% CI, 23-77%) for age-appropriate immunization (five doses) vs partial or no immunization. Vaccine effectiveness increased with increasing number of doses from 25% (95% CI, -58-65%) for three or more doses to 55% (95% CI, -15-83%) for five doses, compared with 0-2 doses.

Effectiveness of a whole cell pertussis vaccine in child-care centers and schools

BACKGROUND

Pertussis has substantially increased in Quebec, Canada, since 1990. We estimated pertussis vaccine effectiveness and vaccine coverage in child-care centers and elementary schools.

METHODS

Two retrospective cohort studies were simultaneously conducted. One included 4482 children attending 88 public child-care centers and the other included 3429 pupils in 14 elementary schools. Cough and pertussis symptoms were assessed through a questionnaire and medical records; immunization status was ascertained by examination of written records.

RESULTS

In child-care centers 95% of children had received at least three vaccine doses at the beginning of the follow-up; in schools more than 98% of pupils had received at least 4 doses. With > or = 4 doses of vaccine and a standard case definition used for surveillance (cough > or = 2 weeks, > or = 1 pertussis symptom and no other apparent cause for cough), vaccine effectiveness was estimated at 61% (95% confidence interval, 44 to 72%) in child-care centers and at 60% (95% confidence interval, 10 to 82%) in schools. With the same number of doses but a case definition requiring a cough > or = 5 weeks, vaccine effectiveness increased to 71% (95% confidence interval, 49 to 83) in child-care centers and to 86% (95% confidence interval, 66 to 94%) in schools.

CONCLUSIONS

The increase in pertussis in Quebec is not caused by a low vaccine coverage. A low vaccine effectiveness may contribute to the resurgence of pertussis in the past decade.

Increased risk of reported pertussis and hospitalization associated with pertussis in low birth weight children

OBJECTIVES

To determine whether low birth weight (LBW) children are at greater risk of reported pertussis and complications of pertussis in the first 2 years of life than are normal birth weight (NBW) children.

STUDY DESIGN

We performed a secondary analysis of three data sets containing statewide information among Wisconsin residents for children born between January 1, 1981, and December 31, 1990. We identified all reported cases of pertussis among children younger than 2 years of age and linked this information with birth certificate data and hospitalization data to determine the relative risk of reported pertussis in LBW compared with NBW children. We also compared the frequency of reported complications of pertussis in LBW and NBW children.

RESULTS

We analyzed reports of 549 pertussis cases; 49 cases occurred in LBW children. The LBW children were significantly more likely to have reported pertussis than were NBW children (relative risk 1.86; 95% confidence interval 1.33, 2.38). The rates of pneumonia and seizures did not differ among LBW and NBW children; however, LBW children with reported pertussis were significantly more likely to be hospitalized than were NBW children (relative risk 1.40; 95% confidence interval 1.11, 1.69).

CONCLUSION

In addition to timely vaccination of all infants, efforts are needed to determine additional ways to reduce the risk of pertussis among LBW infants and children.

A controlled trial of two acellular vaccines and one whole-cell vaccine against pertussis. Progetto Pertosse Working Group

BACKGROUND

Concern about both safety and efficacy has made the use of whole-cell pertussis vaccines controversial. In some European countries, including Italy, the rate of vaccination against pertussis is low.

METHODS

We conducted a double-blind trial in Italy in which infants were randomly assigned to vaccination at two, four, and six months of age with an acellular pertussis vaccine together with diphtheria and tetanus toxoids (DTP); a DTP vaccine containing whole-cell pertussis (manufactured by Connaught Laboratories); or diphtheria and tetanus toxoids without pertussis (DT). The acellular DTP vaccine was either one containing filamentous hemagglutinin, pertactin, and pertussis toxin inactivated with formalin and glutaraldehyde (SmithKline Beecham) or one with filamentous hemagglutinin, pertactin, and genetically detoxified pertussis toxin (Chiron Biocine). Pertussis was defined as 21 days or more of paroxysmal cough, with infection confirmed by culture or serologic testing.

RESULTS

The efficacy of each vaccine, given in three doses, against pertussis was determined for 14,751 children over an average of 17 months, with cases included in the analysis if cough began 30 days or more after the completion of immunization. For both of the acellular DTP vaccines, the efficacy was 84 percent (95 percent confidence intervals, 76 to 89 percent for Biocine DTP and 76 to 90 percent for SmithKline DTP), whereas the efficacy of the whole-cell DTP vaccine was only 36 percent (95 percent confidence interval, 14 to 52 percent). The antibody responses were greater to the acellular vaccines than to the whole-cell vaccine. Local and systemic adverse events were significantly more frequent after the administration of the whole-cell vaccine. For the acellular vaccines, the frequency of adverse events was similar to that in the control (DT) group.

CONCLUSIONS

The two acellular DTP vaccines we studied were safe, immunogenic, and efficacious against pertussis, whereas the efficacy of the whole-cell DTP vaccine was unexpectedly low.