Pertussis infection in fully vaccinated children in day-care centers, Israel

IL-17 and IFN-γ-producing Respiratory Tissue-Resident Memory CD4 T Cells Persist for Decades in Adults Immunized as Children With Whole-Cell Pertussis Vaccines

The objective was to determine if antigen-specific tissue-resident memory T (TRM) cells persist in respiratory tissues of adults immunized as children with whole-cell pertussis (wP) or acellular pertussis (aP) vaccines. Mononuclear cells from tonsil or nasal tissue cells were cultured with Bordetella pertussis antigens and TRM cells quantified by flow cytometry. Adults immunized with wP vaccines as children had significantly more interleukin 17A (IL-17A) and interferon-γ (IFN-γ)-producing TRM cells that respond to B. pertussis antigens in respiratory tissues when compared with aP-primed donors. Our findings demonstrate that wP vaccines induce CD4 TRM cells that can persist in respiratory tissues for decades.

Review of scientific evidence to support recommendations of the full-dose DTaP-IPV vaccination in pre-school age children in Italy

INTRODUCTION

Two vaccine formulations are available to prevent diphtheria, tetanus, pertussis, and poliomyelitis: the pediatric full-dose (DTaP-IPV) and the reduced dose formulation (dTap-IPV). Different immunization schedules are internationally recommended for the pre-school booster dose.

AREAS COVERED

International and Italian recommendations, scientific evidence on immunogenicity and safety of DTaP/dTap vaccines to support the full dose as a pre-school booster and Italian vaccination coverage (VC) up to adolescence.

EXPERT OPINION

The WHO recommends a '3+1' schedule with DTaP vaccine for primary immunization, followed by a pre-school booster with DTaP or dTap vaccine. In Italy, a '2+1' schedule, with no booster in the second year, and a pre-school booster dose are recommended with DTPa-IPV vaccines. Studies showed a non-inferior immunogenicity in dTap vaccinees in pre-school age; nevertheless, the antibody titers were usually greater in children vaccinated with DTaP, while lower frequencies of adverse events were recorded in children receiving dTap. Italian VCs for pre-school and adolescent boosters have not been satisfactory, which further reduced during the COVID-19 period. In Italy, the pre-school booster offers the last chance to receive a full dose of DTaP vaccine, thus, representing the most suitable intervention to provide lasting protection in children.

Tdap vaccination during pregnancy interrupts a twenty-year increase in the incidence of pertussis

Pertussis incidence in developed countries, including Israel, has increased over the past two decades despite the addition of two booster doses in children. However, as pertussis is characterized by a multi-annual periodicity, and since clinical diagnosis can miss cases, determining disease trends at the population level is challenging. To bridge this gap, we developed a simple statistical model to capture the temporal patterns of pertussis incidence in Israel. Our model was calibrated and tested using laboratory-confirmed cases of pertussis for the Israeli population between 1998 and 2019. The model identifies a clear four-year periodicity of pertussis incidence over the past two decades that is identical to the one observed in the pre-vaccine era. Accounting for this periodicity, the model shows a 325% increase in pertussis incidence from 2002 to 2014. These multi-year trends were interrupted shortly after the introduction of routine immunization of Tdap vaccine in pregnancy in 2015, after which we found a 59.7% (95% CI: 57.7-61.6%)decline in pertussis incidence and a 49.5% (36.0-61.6%) decline in hospitalizations compared to the model's projection. While this sharp decline cannot be fully attributed to the newly introduced vaccination policy, sharper reductions of 71.2% (65.6-76.1%) in incidence and 58.4% (39.6-72.7%) in hospitalizations, have been observed in infants of age two months and below - young infants that have yet to become vaccinated and are more likely to be protected by maternal vaccination. Our work suggests that Tdap vaccination during pregnancy is a promising policy for controlling pertussis. Furthermore, due to the stable periodicity of pertussis, public health decision-makers should invest continuous efforts in the implementation of this strategy with additional reinforcement in expected peak years.

Reduction of Direct Health Costs Associated with Pertussis Vaccination with Acellular Vaccines in Children Aged 0-9 Years with Pertussis in Catalonia (Spain)

OBJECTIVES

The aim of this study was to assess direct health costs in children with pertussis aged 0-9 years who were vaccinated, partially vaccinated, and unvaccinated during childhood, and to assess the association between pertussis costs and pertussis vaccination in Catalonia (Spain) in 2012-2013.

METHODS

Direct healthcare costs included pertussis treatment, pertussis detection, and preventive chemotherapy of contacts. Pertussis patients were considered vaccinated when they had received 4-5 doses, and unvaccinated or partially vaccinated when they had received 0-3 doses of vaccine. The Chi square test and the odds ratios were used to compare percentages and the t test was used to compare mean pertussis costs in different groups, considering a p < 0.05 as statistically significant. The correlation between pertussis costs and study variables was assessed using the Spearman's ρ, with a p < 0.05 as statistically significant. Multiple linear regression analysis (IBM-SPSS program) was used to quantify the association of pertussis vaccination and other study variables with pertussis costs.

RESULTS

Vaccinated children with pertussis aged 0-9 years had significantly lower odds ratios of hospitalizations (OR 0.02, p < 0.001), laboratory confirmation (OR 0.21, p < 0.001), and severe disease (OR 0.02, p < 0.001) than unvaccinated or partially vaccinated children with pertussis of the same age. Mean direct healthcare costs were significantly lower (p < 0.001) in vaccinated patients (€190.6) than in unvaccinated patients (€3550.8), partially vaccinated patients (€1116.9), and unvaccinated/partially vaccinated patients (€2330). Multivariable linear regression analysis showed that pertussis vaccination with 4-5 doses was associated with a non-significant reduction of pertussis costs of €107.9 per case after taking into account the effect of other study variables, and €200 per case after taking into account pertussis severity.

CONCLUSIONS

Direct healthcare costs were lower in children with pertussis aged 0-9 years vaccinated with 4-5 doses of acellular vaccines than in unvaccinated or partially vaccinated children with pertussis of the same age.

Pertussis Reinfection in an Adult: A Cause of Persistent Cough Not to Be Ignored

Pertussis is traditionally considered as a disease of the childhood; however, accumulating evidence suggests a stable increase of its incidence among adults and adolescents, during the last decades. Despite the fact that reinfection after natural disease or vaccination is not uncommon, the index of clinical suspicion of pertussis diagnosis in adults remains low. In this article, we report a case of pertussis reinfection 30 years after natural infection, which was complicated by pneumonia, and we discuss our diagnostic and therapeutic approach, aiming to raise clinicians' degree of suspicion regarding pertussis diagnosis in adults. Prompt recognition and appropriate therapy of adult patients can result in the effective control of the symptoms, prevention of severe complications, and spread of the infection to children; thus, they are of great clinical and public health importance.

Density of day cares in relation to reported pertussis incidence in Philadelphia

OBJECTIVES

Reported pertussis incidence has increased markedly in recent years. In addition to the documented increase in under-immunization and waning immunity, the increase may be related to the more frequent use of child care services by parents over the last few decades. Additionally, clustering of outbreaks may be related to neighborhood characteristics not previously identified.

STUDY DESIGN

We conducted a citywide case-control study of children in Philadelphia aged birth through six years, between 2001 and 2013. Cases were reported as probable pertussis diagnoses to the Health Department. Controls were sampled from the city's immunization information system and matched to the cases by date of birth.

METHODS

Multilevel logistic regression was used to isolate the independent contributions of individual and neighborhood risk factors and the corresponding relative odds of pertussis. The density of day cares in each neighborhood served as the main exposure and reported incident cases of confirmed and probable pertussis was the main outcome.

RESULTS

Between 2001 and 2013, 410 cases of confirmed and probable pertussis were included with four controls matched per case yielding a final sample of 2050 children from 45 Philadelphia neighborhoods. There was a 30% increase in the risk of pertussis based solely on the neighborhood where the children resided (median odds ratio 1.3, 95% credible interval 1.1, 1.6). The density of day cares in each neighborhood was unrelated to the distribution of pertussis cases.

CONCLUSIONS

Pertussis clustering was observed at the neighborhood level in Philadelphia, but was unrelated to the neighborhood's day care density. From a Health Department perspective, the highest risk neighborhoods should be targeted for vaccine campaigns and further research to identify the etiologic risk factors.

[Clinical, laboratorial and radiographic predictors of Bordetella pertussis infection]

OBJECTIVE

To identify clinical, laboratorial and radiographic predictors for Bordetella pertussis infection.

METHODS

This was a retrospective study, which analyzed medical records of all patients submitted to a molecular diagnosis (qPCR) for B. pertussis from September 2011 to January 2013. Clinical and laboratorial data were reviewed, including information about age, sex, signs/symptoms, length of hospitalization, blood cell counts, imaging findings, coinfection with other respiratory pathogens and clinical outcome.

RESULTS

222 cases were revised. Of these, 72.5% had proven pertussis, and 60.9% were under 1 year old. In patients aging up to six months, independent predictors for B. pertussis infection were cyanosis (OR 8.0, CI 95% 1.8-36.3; p=0.007) and lymphocyte count >10(4)/μL (OR 10.0, CI 95% 1.8-54.5; p=0.008). No independent predictors of B. pertussis infection could be determined for patients older than six months. Co-infection was found in 21.4% of patients, of which 72.7% were up to six months of age. Adenovirus was the most common agent (40.9%). In these patients, we were not able to identify any clinical features to detect patients presenting with a respiratory co-infection, even though longer hospital stay was observed in patients with co-infections (12 vs. 6 days; p=0.009).

CONCLUSIONS

Cyanosis and lymphocytosis are independent predictors for pertussis in children up to 6 months old.

Live pertussis vaccines: will they protect against carriage and spread of pertussis?

Pertussis is a severe respiratory disease that can be fatal in young infants. Its main aetiological agent is the Gram-negative micro-organism Bordetella pertussis. Vaccines against the disease have been in use since the 1950s, and global vaccination coverage has now reached more than 85%. Nevertheless, the disease has not been controlled in any country, and has even made a spectacular come-back in the industrialized world, where the first-generation whole-cell vaccines have been replaced by the more recent, less reactogenic, acellular vaccines. Several hypotheses have been proposed to explain these observations, including the fast waning of acellular vaccine-induced protection. However, recent mathematical modelling studies have indicated that asymptomatic transmission of B. pertussis may be the main reason for the current resurgence of pertussis. Recent studies in non-human primates have shown that neither whole-cell, nor acellular vaccines prevent infection and transmission of B. pertussis, in contrast to prior exposure. New vaccines that can be applied nasally to mimic natural infection without causing disease may therefore be useful for long-term control of pertussis. Several vaccine candidates have been proposed, the most advanced of which is the genetically attenuated B. pertussis strain BPZE1. This vaccine candidate has successfully completed a first-in-man phase I trial and was shown to be safe in young male volunteers, able to transiently colonize the nasopharynx and to induce antibody responses to B. pertussis antigens in all colonized individuals. Whether BPZE1 will indeed be useful to ultimately control pertussis obviously needs to be assessed by carefully conducted human efficacy trials.

A new socioeconomic status measure for vaccine research in children using individual housing data: a population-based case-control study

Background

We recently developed HOUSES, an individual housing-based socioeconomic status (SES) measurement for health disparities research. We assessed whether HOUSES was associated with risk of pertussis and pertussis vaccine up-to-date status in children.

Methods

The study utilized a previous population-based case-control study cohort assembled during the 2004–2005 pertussis outbreak. We collected data on pertussis vaccine status (up-to-date status) at the time of the index date. Using a z-score for housing value, actual square footage, and numbers of bedrooms and bathrooms, HOUSES was formulated in continuous variable and categorized into quartiles. Vaccine up-to-date status was compared among subjects with different SES as measured by HOUSES using a chi-square test and logistic regression models.

Results

Of the 391 eligible pediatric subjects (median age of 13.1 years with male sex of 55 %), 363 (93 %) were successfully geocoded to formulate HOUSES index. HOUSES was not associated with the risk of pertussis (p = 0.82). Pertussis vaccine up-to-date statuses were 79, 86, 83, and 94 % for children in the first (the lowest SES), second, third, and fourth quartiles of HOUSES, respectively (p = 0.03). HOUSES as a continuous variable was associated with pertussis vaccine up-to-date status (adjusted OR: 1.15 per increment of one unit of HOUSES, 95 % CI: 1.04–1.27, p = 0.008).

Conclusion

While HOUSES is not associated with the risk of pertussis, it predicts vaccine up-to-date status among children with different SES. HOUSES may be a useful tool for vaccine delivery research among children.

Infection Prevention and Control in Residential Facilities for Pediatric Patients and Their Families

The Society for Healthcare Epidemiology of America (SHEA) guideline “Infection Prevention and Control in Residential Facilities for Pediatric Patients and Their Families” is the first infection prevention and control (IPC) guideline to address preventing transmission of infectious agents in “home away from home” residential settings, of which the Ronald McDonald Houses (RMHs) serve as a prototype. These types of facilities provide support services, including overnight lodging, for ill and injured children and their families. Food preparation occurs in common areas, and cleaning of rooms or apartments is performed by the occupants during their stay and before departure. Pediatric patients are frequent guests of the family-centered facilities while receiving or recovering from specialized medical therapy. Examples of high-risk populations served in these facilities include families of patients with cancer, recipients of stem cell or solid organ transplants, surgical and/or very-low-birthweight infants who receive care in neonatal intensive care units (NICUs), those with cystic fibrosis, and women with high-risk pregnancies awaiting delivery in a nearby medical center. Such facilities are located worldwide and vary in their physical structure and the predominant population served.

Clinical, laboratorial and radiographic predictors of Bordetella pertussis infection

OBJECTIVE: To identify clinical, laboratorial and radiographic predictors for Bordetella pertussis infection.METHODS: This was a retrospective study, which analyzed medical records of all patients submitted to a molecular dignosis (qPCR) for B. pertussis from September 2011 to January 2013. Clinical and laboratorial data were reviewed, including information about age, sex, signs/symptoms, length of hospitalization, blood cell counts, imaging findings, coinfection with other respiratory pathogens and clinical outcome.RESULTS: 222 cases were revised. Of these, 72.5% had proven pertussis, and 60.9% were under 1 year old. In patients aging up to six months, independent predictors for B. pertussisinfection were (OR 8.0, CI 95% 1.8-36.3; p=0.007) and lymphocyte count >104/µL (OR 10.0, CI 95% 1.8-54.5; p=0.008). No independent predictors of B. pertussisinfection could be determined for patients older than six months. Co-infection was found in 21.4% of patients, of which 72.7% were up to six months of age. Adenovirus was the most common agent (40.9%). In these patients, we were not able to identify any clinical features to detect patients presenting with a respiratory co-infection, even though longer hospital stay was observed in patients with co-infections (12 vs. 6 days; p=0.009).CONCLUSIONS: Cyanosis and lymphocytosis are independent predictors for pertussis in children up to 6 months old.

Pertussis. A reemerging and an underreported infectious disease

Pertussis or whooping cough is a highly infectious, vaccine preventable disease. The incidence of the disease  has greatly been reduced since the introduction of the diphtheria, tetanus, pertussis vaccine. Pertussis resurgence has been observed in highly vaccinated populations of Western countries since 1990s. Poor vaccine quality, waning vaccine induced immunity, pathogen adaptation, and enhanced surveillance as well as advancements in diagnostic facilities are some of the reasons considered responsible for the increased reporting of pertussis cases. Pertussis may have been ignored and unnoticed due to its atypical manifestations in partially immunized population or people with waning immunity. We review the reports of pertussis resurgence from different countries and attempt to investigate reasons behind the reappearance of the disease. Pertussis is still an under reported disease and the available data from the developing countries is not a true picture of the story.  Therefore, developing countries need to improve their surveillance systems. 

Cocooning: a concept to protect young children from infectious diseases

PURPOSE OF REVIEW

Despite focused efforts aimed at preventing infectious diseases among infants, recent years have seen a surge of infections among this population, particularly in pertussis, reminiscent of the 1940s prevaccine era. Given these trends, this review serves to discuss cocooning for infants against pertussis and its more recent application in influenza, and the barriers to and facilitators of this important strategy.

RECENT FINDINGS

Infection with pertussis and influenza remains a significant cause of hospitalization among infants aged less than 1 year. Simultaneously, uptake of both tetanus, diphtheria, and acellular pertussis (Tdap) and influenza vaccines is very low among adults reporting close contact with an infant. To date, widespread implementation of cocooning has been thwarted by both individual-level and system-level issues, although general acceptance of vaccination is high in settings in which cocooning is encouraged.

SUMMARY

Better characterization and improvement of the cocooning strategy are necessary. Additionally, longitudinal research evaluating the effectiveness of cocooning against pertussis and influenza is essential. Ultimately, the effectiveness of cocooning to produce sustained control of infections will be dependent on healthcare provider advocacy, patient education, implementation and enforcement of policies, and the development of cost-effective programs.

Update on pertussis and pertussis immunization

Pertussis is a highly contagious respiratory tract disease caused by Bordetella pertussis infection. The clinical manifestation of this infection can be severe enough to cause death. Although pertussis has been supposed to be a vaccine-preventable disease ever since the widespread vaccination of children against pertussis was started, since the 1990s, cases of pertussis and related fatalities are on the rise, especially in countries with high vaccination coverage. In Korea, there have been no deaths due to pertussis since 1990, and the vaccination rate continues to be approximately 94%. However, the number of pertussis cases reported to the Korea Center for Disease Control and Prevention has tended to increase in the 2000s, and in 2009, there was an obvious increase in the number of pertussis cases reported. This review aims to present the latest information about the pathogenesis, diagnosis, treatment, and prevention of pertussis.

The seroepidemiology of Bordetella pertussis in Israel--Estimate of incidence of infection

This study was undertaken to estimate the magnitude of Bordetella pertussis infections in a highly vaccinated population in Israel in order to evaluate the relationship between clinical notification data and serology-based evidence of infection. A cross-sectional survey was conducted on a total of 1982 serum samples from the National Serum Bank, collected from January 2000 through December 2001, in order to monitor high levels of pertussis toxin (PT) IgG antibody indicative of recent B. pertussis infection, by standardized methods. The estimation yielded an infection incidence rate of 2448 per 100,000 population (> or =3 years of age) for the year 2000 compared to an annual incidence of reported pertussis of 5.6 per 100,000 for the same period. The peaks of estimated incidence of infection were found in the groups of 15-19-year olds (5245 per 100,000) and older than 60 years (6469 per 100,000), whereas the majority of clinical pertussis cases were reported for the 10-14-year olds (20.5 per 100,000). The findings clearly show that despite a high vaccination coverage rate (>93%), there is still a considerable circulation of B. pertussis, particularly in adolescents and elderly. Population-based serosurveillance for pertussis offers the potential to assist interpretation of trends independent of notification and diagnostic bias.

Estimating the duration of pertussis immunity using epidemiological signatures

Case notifications of pertussis have shown an increase in a number of countries with high rates of routine pediatric immunization. This has led to significant public health concerns over a possible pertussis re-emergence. A leading proposed explanation for the observed increase in incidence is the loss of immunity to pertussis, which is known to occur after both natural infection and vaccination. Little is known, however, about the typical duration of immunity and its epidemiological implications. Here, we analyze a simple mathematical model, exploring specifically the inter-epidemic period and fade-out frequency. These predictions are then contrasted with detailed incidence data for England and Wales. We find model output to be most sensitive to assumptions concerning naturally acquired immunity, which allows us to estimate the average duration of immunity. Our results support a period of natural immunity that is, on average, long-lasting (at least 30 years) but inherently variable.

The eradication of vaccine-preventable infectious diseases remains an important public health priority. To achieve this goal, the level of immunity afforded needs to be high and long-lasting. For pertussis, one of the leading causes of mortality in infants, immunity has been shown to wane in some individuals. The epidemiological impacts of this observation depend critically on the duration of protective immunity in the entire population, which remains notoriously difficult to estimate. We approach this problem by exploring the agreement between model dynamics and case notification data from England & Wales. Our estimates suggest the average duration of immunity is much longer than is currently thought (at least 30 years), but that some individuals would lose immunity quite rapidly.

Use of Bordetella pertussis BP3385 to establish a cutoff value for an IS481-targeted real-time PCR assay

This study utilized the Bordetella pertussis single-copy PCR target BP3385 as a means of confirming IS481 PCR-positive reactions with cycle threshold (C(T)) values of >35. IS481 PCRs with C(T) values of >35 cycles may represent PCR conditions where there is <1 CFU of B. pertussis per PCR.

Factors contributing to pertussis resurgence

Despite extensive immunization, the disease pertussis remains one of the world’s leading causes of vaccine-preventable deaths. An estimated 50 million cases and 300,000 deaths occur every year. A resurgence of pertussis is observed in highly immunized populations. Increasing numbers of pertussis are reported in adolescents and adults who transmit bacteria to newborns and infants to whom pertussis may be a life-threatening disease. Many studies have shown that the causes for the resurgence are multiple, such as increased awareness of disease, use of better diagnostic tools, improved surveillance methods and waning vaccine-induced immunity. Recently, antigenic divergence has been found between vaccine strains and clinical isolates in many countries with high vaccination coverage. Here, we summarize these findings and discuss the factors contributing to pertussis resurgence in immunized populations.

What is new in pertussis?

Despite high vaccination coverage, over the last fifteen years there has been a worldwide resurgence of B. pertussis infection. While classical pertussis in the prevaccine era was primarily a childhood disease, today with widespread vaccination, there has been a shift in the incidence of disease to adolescents and adults. Centers of Disease Control and Prevention (CDC) data from 2004 reveal a nearly 19-fold increase in the number of cases in individuals 10-19 years and a 16-fold increase in persons over 20 years. Indeed adolescent and adults play a significant role in the transmission of pertussis to neonates and infants who are vulnerable to substantial morbidity and mortality from pertussis infection. Several explanations have been proposed to explain the increasing incidence of disease, with waning immunity after natural infection or immunization being widely cited as a significant factor. Improving molecular biology diagnostic techniques, namely PCR assays, also accounts for the increasing laboratory diagnosis of pertussis. Expanding vaccination strategies including universal immunization of adolescents, targeted immunization of adults, and in particular, healthcare workers, childcare providers and parents of newborns, will likely improve pertussis control. With pertussis continuing to pose a serious threat to infants, and greatly affecting adolescents and adults, there remains a need to: (a) increase the awareness of physicians as to the growing pertussis problem, (b) standardize diagnostic techniques, and (c) implement various new vaccine strategies to enhance its control.

Cough symptoms in children aged 5-14 years in Sydney, Australia: non-specific cough or unrecognized pertussis?

OBJECTIVE

The aim of this study was to estimate the community prevalence of coughing symptoms, consistent with surveillance definitions for pertussis, and doctor-diagnosed pertussis in children aged 5-14 years.

METHODOLOGY

A telephone survey of a cross-sectional community sample of parents regarding their child's cough symptoms in the previous 12 months was undertaken in a representative Australian urban region.

RESULTS

In 2020 interviews, parents reported that 22% of children had a cough lasting 2 weeks or longer in the preceding 12 months, and 14% (283) had additional symptoms meeting the Centers for Disease Control (CDC) case definition for pertussis. A cough meeting the case definition was significantly more commonly reported by parents of children aged 5-9 years (17%; P < 0.001) but reported exposure to diagnosed pertussis in such cases was significantly more common in children aged 10-14 years (4.3%; odds ratio 12.8; P < 0.01). Parents of 90% of children meeting the CDC case definition sought medical advice. A diagnosis of pertussis was reported in only 1.2% of cases, which extrapolates to an annual incidence of doctor-diagnosed pertussis of 347/100,000 (95% confidence interval, 140-714 per 100,000). This contrasts with 29/100,000 notified cases in the same age group, time period and geographic area.

CONCLUSION

Cough episodes meeting a clinical case definition for pertussis commonly used in surveillance are reported by a high proportion of carers of school-aged children in Australia. The majority of children who met the CDC and Australian case definitions for pertussis and sought medical attention were not identified as potentially having pertussis, suggesting underdiagnosis of pertussis. Even if less than half of this is true pertussis, the potential impact in terms of transmission of pertussis in the community is likely to be high. The reported incidence of doctor-diagnosed disease estimated from this survey was at least five and up to 20 times the official notification rate. More work needs to be done in raising awareness among medical practitioners of pertussis as a differential diagnosis in older children and adolescents with cough.

Epidemiology of pertussis

The World Health Organization recommended that a pertussis incidence of <1 case per 100,000 population be achieved in Europe by 2000. Available data indicate that this goal has generally not been achieved, and the incidence is actually rising in some countries. Understanding the reasons for this increased incidence may lead to better global control of pertussis. In the majority of countries where pertussis is a notifiable disease, a case-based national surveillance system is in place. However, different case definitions, methods of diagnosis and reporting and surveillance systems make direct intercountry comparisons difficult, and pertussis is not a statutory notifiable disease in every country. Nevertheless the general consensus is that reported incidences are probably considerably lower than the actual incidence of pertussis; underreporting is common. Prolonged cough may be the only clinical feature in adolescents or adults, who may present for diagnosis late (precluding laboratory confirmation) or not at all. When they do present, their condition is often misdiagnosed because, in part, clinicians continue to perceive pertussis as a childhood disease. Despite underreporting, an increased incidence of infant, adolescent and adult pertussis has been observed worldwide since the introduction of widespread vaccination. This is of concern because adolescents and adults have been identified as a source of transmission of pertussis to very young infants who are unimmunized or partially immunized and thus more vulnerable to disease-related complications and higher mortality. In recent years, acellular pertussis vaccines have been incorporated into the immunization schedules of many developed countries, gradually replacing whole cell vaccines. Dosing schedules vary between countries, although primary immunization with 3 doses of the pertussis vaccine within the first 6 months of life exists in most countries. Only Australia, Austria, Canada, France and Germany have incorporated an adolescent booster dose into their current immunization schedules, in recognition of the rising incidence of pertussis in adolescents and adults. Despite high coverage rates for primary immunization in infants and children, pertussis continues to be a global concern, with increased incidence widely noted. This global epidemiologic summary highlights differences worldwide in pertussis reporting, incidence and approaches to prevention. It underscores a general shift in the age distribution of pertussis toward older groups. Understanding the link between these observations may lead to better informed global control strategies, especially those pertaining to immunization schedules and use of pertussis vaccine.

Pertussis vaccination for adolescents and adults

Following the introduction of vaccines, the incidence of pertussis declined; however, since 1990, a progressive increase was noted, even in highly immunised populations. Periodic pertussis outbreaks are due to suboptimal efficacy of the vaccine and waning immunity with increasing age. A significant proportion of adolescents and adults with a prolonged cough present Bordetella pertussis, and infection is often transmitted to infants too young to be vaccinated. A high vaccination coverage in the whole population would be necessary to interrupt the circulation of B. pertussis, but immunisation programmes for adolescents and adults have been introduced recently and are accepted with difficulty. The lack of cost-benefit analysis and consistent epidemiological data makes it difficult to assess the role of pertussis elimination among public health priorities. At present, programmes targeted at risk groups for close contacts with infants are the most convenient for adult population, as more epidemiological and economic evidence is needed before a universal strategy can be discussed.

Adolescent and adult pertussis vaccination: computer simulations of five new strategies

Approximately one million adult pertussis cases occur annually in the US, and infants still die from pertussis. Computer simulations were used to predict the impact of vaccination of children, adults and/or adolescents, and household members of newborns (cocoon strategy). Childhood vaccination greatly reduced cases in children, but increased the incidence in adolescents and adults. Routine adolescent and adult vaccination had a large direct effect, whereas the cocoon strategy had a predominantly indirect effect on young infants. The number needed to vaccinate (NNV) to prevent a case of typical pertussis in the entire population was lowest for the adolescent strategy. The cocoon strategy had the lowest NNV to prevent a case of typical pertussis in young infants. The current vaccination schedule, local epidemiological data, age-specific cost of pertussis cases, and accessibility of the target population will determine which strategy has the highest likelihood of success in achieving the public health goal.

Molecular typing of Bordetella pertussis isolates recovered from Belgian children and their household members

Recently, a moderate increase in the prevalence of pertussis, possibly contracted from adults, has been observed among unvaccinated children. During a 3-year period, we prospectively enrolled 93 index patients with a polymerase chain reaction (PCR) and/or culture result positive for Bordetella pertussis. Among 63 household contacts of 28 index patients, PCR and culture for B. pertussis identified 25 B. pertussis-positive persons. Nineteen of 25 B. pertussis-positive household contacts were asymptomatic. Isolates were available from 10 families of both index patients and household contacts for molecular typing by pulsed-field gel electrophoresis (PFGE) and for genotyping of pertactin and pertussis toxin by sequence-specific PCR and sequencing. PFGE demonstrated homogeneity among the isolates recovered from within each family but heterogeneity among the isolates recovered from different families. B. pertussis isolates recovered from index patients and their household contacts were indistinguishable by molecular typing, demonstrating that identical strains can cause full pertussis disease in children and asymptomatic infection in adults and adolescents.

The potential cost-effectiveness of acellular pertussis booster vaccination in England and Wales

A cost-effectiveness analysis of the introduction of acellular pertussis booster doses at either 4 or 15 years of age was performed. A transmission dynamic model was used to predict the level of indirect protection in those too young to be vaccinated. Multivariate sensitivity analyses were performed. In England and Wales there are an estimated 35,000 general practitioner (GP) consultations, 5500 inpatient days, and nine deaths annually attributable to pertussis, despite high levels of coverage for the primary course (approximately 95%). Around 80% of the bed-days and 90% of the deaths occur in those too young to be immunised (< 3 months of age). The introduction of acellular booster doses at 4 years is expected to reduce morbidity and mortality in the younger age groups by 40-100%, and at 15 years by 0-100%. From the perspective of the health care provider, roughly 50% of the simulations result in a cost per life-year gained of less than 10,000 pounds for vaccination at 4 years, the corresponding proportion for vaccination at 15 years being only 35%. Apart from the degree of indirect protection the model was most sensitive to the discount rate, the price of the vaccine, and the mortality rate. Significant uncertainty remains regarding the epidemiology of pertussis and the impact of booster doses. Nevertheless, the introduction of acellular boosters, particularly at 4 years, has the potential to be cost-effective in the UK.

Pertussis: an old disease that is still with us

Our knowledge of pathogenesis, clinical presentation and prevention of pertussis has improved substantially over recent years. We now better understand the function of long-known virulence factors for Bordetella pertussis, and genome sequencing has identified a multitude of new proteins; their functions are yet to be elucidated. Furthermore, improved diagnostic tools have revealed the broad spectrum of disease, and new insights into the host's immune response have been gained. Finally, the development, evaluation, licensing and implementation of several new acellular pertussis vaccines with high acceptance have changed the epidemiology of pertussis in many countries (i.e. a shift towards an increasing burden of disease in adolescent persons and adults). These developments are likely to have great impact on the daily practice not only of paediatricians, but also of general practitioners, internists, gynaecologists and many other specialists in adolescent and adult medicine. The present review provides an update on recent progress.