The Global Pertussis Initiative: Report from a Round Table Meeting to discuss the epidemiology and detection of pertussis, Paris, France, 11–12 January 2010

Pathogenicity and virulence of Bordetella pertussis and its adaptation to its strictly human host

The highly contagious whooping cough agent Bordetella pertussis has evolved as a human-restricted pathogen from a progenitor which also gave rise to Bordetella parapertussis and Bordetella bronchiseptica. While the latter colonizes a broad range of mammals and is able to survive in the environment, B. pertussis has lost its ability to survive outside its host through massive genome decay. Instead, it has become a highly successful human pathogen by the acquisition of tightly regulated virulence factors and evolutionary adaptation of its metabolism to its particular niche. By the deployment of an arsenal of highly sophisticated virulence factors it overcomes many of the innate immune defenses. It also interferes with vaccine-induced adaptive immunity by various mechanisms. Here, we review data from invitro, human and animal models to illustrate the mechanisms of adaptation to the human respiratory tract and provide evidence of ongoing evolutionary adaptation as a highly successful human pathogen.

Estimating Bordetella pertussis seroprevalence in adolescents and young adults in Mexico using the 2012 National Health and Nutrition Survey (ENSANUT)

BACKGROUND

Low vaccination rates and under-detection of pertussis infections in adolescents and young adults have an impact on the transmission of pertussis to infants. In this study, the proportion of adolescents and young adults with IgG antibodies against B. pertussis antigens, representing recent infection or vaccination, was estimated in a population-based probabilistic survey in Mexico.

METHODS

Sera and data from 1,581 subjects, including 1,102 adolescents and 479 young adults (10-19 and 20-25 years old, respectively) randomly selected from Mexico's 2012 National Health and Nutrition Survey, were analyzed. IgG antibodies against pertussis toxin (PT) were measured with the CDC/FDA ELISA. A subset of 234 samples was additionally tested with Bp-IgG PT ELISA kit (EUROIMMUN AG, Lubeck, Germany). Threshold values from corresponding test kits were used to identify recent infection or vaccination.

RESULTS

Overall anti-PT IgG seroprevalence was 3.9% (95% CI: 2.3-6.3); 3.1% (95% CI: 1.9-5.0) in adolescents, and 4.9% (95% CI: 2.2-11) in young adults. Seroprevalence did not significantly vary by sex, socioeconomic status, region or rural/urban location. Compared to the CDC/FDA ELISA, the EUROIMMUN test showed a 76% sensitivity and 88% specificity. The weighted estimates represent a considerable burden of recent infection in adolescents and young adults; however, most adolescents and adults were seronegative and, therefore, susceptible to pertussis infection.

CONCLUSION

Since booster vaccination to B. pertussis after toddlerhood is not recommended in the Mexican national policy, anti-PT IgG seropositivity may be reasonably attributed to recent infection. Assessing pertussis seroprevalence requires careful consideration of the diagnostic test threshold interpretation and epidemiological model used.

Bordetella pertussis in School-Age Children, Adolescents and Adults: A Systematic Review of Epidemiology and Mortality in Europe

Pertussis (whooping cough) epidemics persist globally despite high vaccine coverage among infants and young children. The resurgence of pertussis in high-income countries is partly due to waning vaccine immunity, resulting in a pool of unprotected adolescents and adults. However, pertussis is generally less severe in adolescents and adults, and this difference in presentation means it can often be unrecognised by healthcare professionals, meaning that it is largely under-diagnosed in older populations. A systematic search of MEDLINE, EMBASE and BIOSIS was undertaken to identify studies published between 1 January 1990 and 17 June 2019, with information on pertussis epidemiology and mortality in school-aged children, adolescents and adults in Europe. A formal statistical comparison (e.g. using meta-analyses) was not possible because of the mix of methodologies reported. There were 69 epidemiological studies and 19 mortality studies identified for review. Over the past decade, the reported incidence of notified pertussis cases varied widely between European countries, which is likely associated with differences in surveillance systems, diagnostic techniques and reporting regulations. However, several studies show that pertussis is circulating among adolescents and adults in Europe, and although pertussis-related morbidity and mortality are highest in infants, there is evidence that adults aged > 50 years are at increased risk. For example, in a hospital-based surveillance study in Portugal, between 2000 and 2015, 94% of hospitalised pertussis cases were infants aged < 1 year, with a case fatality rate (CFR) of 0.8%; however, among hospitalised adult cases of pertussis, the CFRs were 11.5% (aged 18–64 years) and 17.4% (aged > 65 years). Very few European countries currently include pertussis boosters for adults in the national immunisation strategy. In addition to increasing pertussis vaccination coverage in adolescents and adults, mitigation strategies in European countries should include improved diagnosis and treatment in these populations.

Bordetella pertussis in School-Age Children, Adolescents, and Adults: A Systematic Review of Epidemiology, Burden, and Mortality in Asia

Cyclic epidemics of pertussis (whooping cough) have been observed globally over the past twenty years despite high infant vaccine coverage. The resurgence of pertussis in high-income countries is partly due to waning vaccine immunity in older children and adults, as well as better surveillance and diagnostics. Moreover, in adolescents and adults, pertussis symptoms are mild and similar to common cough syndromes, meaning that it is under-diagnosed in older populations. A systematic search of MEDLINE, EMBASE, and BIOSIS was undertaken to identify studies published between 1 January 1990 and 17 June 2019, with information on pertussis epidemiology, burden of illness, and mortality in school-aged children, adolescents, and adults in Asia. Studies identified for inclusion were reviewed narratively because a statistical comparison was not possible due to the mix of methodologies used. The results showed that in East Asia, including Japan, South Korea, China, and Taiwan, pertussis is circulating in older children and adults. Diphtheria-tetanus-pertussis (DTP4) coverage is high in East Asia, yet outbreaks observed in Japan and South Korea suggest that vaccine-acquired immunity had waned in adolescents and adults. Several school outbreaks in China show that pertussis is circulating in young children, with continued circulation in adolescents and adults. There was a lack of information from Southeast/South Asian countries, although pan-Asian serosurveys showed that recent pertussis infection was common in adolescents and in adults with persistent cough. To conclude, the circulation of pertussis in Asian countries with high DTP4 coverage supports the expansion of routine vaccination to include booster doses for children at school entry and adolescents. However, surveillance is weak or absent in many countries, meaning that the true burden of pertussis, particularly among older populations, is unknown.

Bordetella pertussis in School-Age Children, Adolescents, and Adults: A Systematic Review of Epidemiology, Burden, and Mortality in Africa

The Global Pertussis Initiative recommends diphtheria–tetanus–pertussis (DTP3) vaccination of infants aged < 1 year for all African countries, and recommends the vaccination of pregnant women as a primary prevention strategy. However, the role of older children and adults in the transmission of pertussis in Africa is not clear. A systematic search of MEDLINE, EMBASE, and BIOSIS was undertaken to identify studies published between 1 January 1990 and 17 June 2019, with information on pertussis epidemiology, burden of illness, and mortality in school-aged children, adolescents, and adults in Africa. Studies identified for inclusion were reviewed narratively because a statistical comparison was not possible because of the mix of methodologies used.

Studies from North Africa (Morocco, Tunisia, and Algeria) reported that although DTP4 vaccine coverage is high, severe pertussis-related complications persist in young children, vaccine-acquired immunity wanes in adolescents, and household contacts are important transmitters of infection. A serosurvey in Gambia showed that 6% of the general population had pertussis antibody levels suggesting recent infection, and studies from Senegal showed that pertussis infection was endemic despite high DTP3 coverage. During a pertussis outbreak in Ethiopia, the case fatality rate was 3.7% overall, and 6.3% among children aged 5–9 years. In a case-surveillance study in South Africa, the incidence of pertussis among hospitalized children was 526/100,000, and infection rates were higher in HIV-exposed and -infected children compared with uninfected children. In conclusion, the highest burden of pertussis in Africa is among infants, and surveillance is lacking in many African countries meaning that the burden of pertussis among infants and infection rates among older children and adults are not well reported, and likely underestimated.

A data driven clinical algorithm for differential diagnosis of pertussis and other respiratory infections in infants

Background

Clinical criteria for pertussis diagnosis and clinical case definitions for surveillance are based on a cough lasting two or more weeks. As several pertussis cases seek care earlier, a clinical tool independent of cough duration may support earlier recognition. We developed a data-driven algorithm aimed at predicting a laboratory confirmed pertussis.

Methods

We enrolled children <12 months of age presenting with apnoea, paroxistic cough, whooping, or post-tussive vomiting, irrespective of the duration of cough. Patients underwent a RT-PCR test for pertussis and other viruses. Through a logistic regression model, we identified symptoms associated with laboratory confirmed pertussis. We then developed a predictive decision tree through Quinlan's C4.5 algorithm to predict laboratory confirmed pertussis.

Results

We enrolled 543 children, of which 160 had a positive RT-PCR for pertussis. A suspicion of pertussis by a physician (aOR 5.44) or a blood count showing leukocytosis and lymphocytosis (aOR 4.48) were highly predictive of lab confirmed pertussis. An algorithm including a suspicion of pertussis by a physician, whooping, cyanosis and absence of fever was accurate (79.9%) and specific (94.0%) and had high positive and negative predictive values (PPV 76.3% NPV 80.7%).

Conclusions

An algorithm based on clinical symptoms, not including the duration of cough, is accurate and has high predictive values for lab confirmed pertussis. Such a tool may be useful in low resource settings where lab confirmation is unavailable, to guide differential diagnosis and clinical decisions. Algorithms may also be useful to improve surveillance for pertussis and anticipating classification of cases.

Association of weather variability with resurging pertussis infections among different age groups: A non-linear approach

Pertussis has resurged in many countries over recent years, especially among adolescents and adults. This study assessed the effect of weather variability on resurging pertussis among different age groups in Jinan, China. Data on weekly pertussis notifications by age group and weather factors (mean temperature (MeanT), mean temperature standard deviation within a week (MeanT SD), diurnal temperature range (DTR) and relative humidity (RH)) were collected between 2013 and 2017. Distributed lag non-linear models (DLNMs) and regression tree models were used to examine the non-linear association between weather variability and pertussis infections. The 2-weeks cumulative relative risk (RR) of pertussis infections was 4.46 (95% confidence interval (CI): 2.33-9.51) in 0-4 age group, 6.25 (95% CI: 1.38-22.76) in 5-9 age group and 10.11 (95% CI: 2.83-39.07) in 10+ age group when MeanT was at 30.0 °C. MeanT SD (RR range in the three age groups: 2.82-5.83), DTR (RR range: 6.33-11.56) and RH (RR range: 2.02-7.43) also exert significant influence, with the highest risks at 10+ age group. Regression tree models showed the interactive effects of weather variability. The mean pertussis infections increased by over 1.7-fold in 0-4 years group when MeanT ≥14 °C, RH ≥57% and DTR ≥10 °C; by over 2.3-fold in 5-9 years group when MeanT ≥20 °C and MeanT SD ≥3 °C; by 2.0-fold in 10+ years group when MeanT ≥0.7 °C, DTR ≥8.3 °C and RH ≥74%. The study found significantly different associations between weather variability and pertussis infections by age group, and appeared to be stronger in 10+ years group. Continuing climate change, together with other risk factors such as low antibody levels among adolescents and adults, may facilitate pertussis resurgence. This supports previous suggestions of carefully reconsidering current vaccination programme to effectively curb the resurgence of pertussis.

Trends in Hospital Admissions for Pertussis Infection: A Nationwide Retrospective Observational Study in Italy, 2002-2016

Background: Pertussis is a highly contagious infectious disease which continues to be an important public-health issue despite the high immunization coverage rates achieved. However, evidence of increased circulation of pertussis among adolescents and adults due to waning immunity and atypical clinical manifestations seem to be the main reasons for its resurgence. The aim of this study was the analysis of the epidemiological trend for pertussis-related hospitalizations in Italy, in relation with vaccination coverage and information from laboratory confirmed cases of pertussis. Methods: A retrospective observational study investigating hospitalizations for pertussis from 2002 to 2016 in Italy was conducted. Frequencies and rates of hospitalization were analyzed and hospitalization data were compared with a series of already published laboratory confirmed data. Results: This study highlighted a rising trend for pertussis hospitalizations in Italy since 2008. Infants aged <1 year showed the highest frequencies (63.39%) and average rates (74.60 × 100000 infants) of hospitalization despite an extremely high vaccination coverage (95.89%). An increasing trend of hospitalization frequency emerged for the age group with levels of IgG antibodies to pertussis toxin compatible with pertussis infection within the last year (20–29 years old age group). Conclusions: The rising trend for pertussis hospitalizations and the greater involvement of infants aged <1 year require an integrated approach, including the implementation of booster doses administration in adolescence and adulthood, the vaccination of pregnant women and the cocoon strategy.

Impact of Pertussis on the Italian population: Analysis of hospital discharge records in the period 2001-2014

OBJECTIVES

The study aimed to analyze and update the impact of pertussis on the Italian population by evaluating pertussis-related hospital admissions in the period 2001-2014.

DESIGN OR METHODS

Hospital Discharge Records (HDR) were provided by the National Archive of HDR data of the Ministry of Health. Only hospitalizations included in the primary diagnosis were evaluated. Significant trends over the considered years were assessed as average annual percent changes (AAPC) applying the Joinpoint model.

RESULTS

A total of 7,102 hospital admissions for pertussis (main diagnosis) were registered; the trend of hospitalizations progressively decreased from >1/100,000 inhabitants in the years 2001-2004 to 0.64/100,000 inhabitants in 2014. A great part of hospitalizations (63.6%) involved subjects <1 year of life; almost 20% of cases were registered in the age class 5-14 years. The Joinpoint analysis showed a statistically significant variation in some age classes.

CONCLUSIONS

Even if this study shows a decreasing trend in the number of pertussis-related hospitalizations, the impact of the disease in Italy in terms of hospital admissions continues to be relevant, especially in the <1 year age class. Pertussis therefore continues to be, in Italy as well as in other European countries, an important public health issue.

Therapeutic effect of vitamin K1 combined with meropenem on the treatment of pertussis syndrome

Clinical efficacy of vitamin K1 combined with meropenem on the treatment of pertussis syndrome was evaluated. Clinical data of 170 children with pertussis syndrome treated in the Second People's Hospital of Liaocheng from March 2015 to March 2017 were collected. Of these, 87 patients who were treated with vitamin K1 combined with meropenem were regarded as the experiment group. A total of 83 patients who were treated with meropenem alone were regarded as the control group. Both groups were treated with anti-infective, respiratory support, antispasmodic, expectorant and other basic treatments. The therapeutic effects, duration of spasmodic cough, length of hospitalization, antipyretic time, duration of voice disappearance and healing time were observed between the two groups. The duration of spasmodic cough and length of hospitalization in the experiment were lower than the control group, and the difference was statistically significant between the groups (P<0.05). The explicit efficiency (51.72%) and total effective efficiency (99.55%) in the experiment group were significantly higher than the explicit efficiency (36.14%) and total effective efficiency (78.31%) in the control group. There was a statistically significant difference between the groups (P<0.05). The voice disappearance time and healing time in the experiment group were significantly shorter than the control group, and there was a statistically significant difference between the groups (P<0.05). The antipyretic time in the experiment group was lower than that of the control group, the difference between the groups was not statistically significant (P>0.05). The treatment with vitamin K1 and meropenem has a significant effect in relieving pediatric pertussis syndrome, it can shorten the duration of spasmodic cough, antipyretic time, duration of voice disappearance and length of hospitalization in children with pertussis syndrome, and improve the efficacy clinically.

[Prevalence of Bordetella pertussis infection in children with chronic cough and its clinical features]

OBJECTIVE

To investigate the prevalence of Bordetella pertussis infection in children with chronic cough and its clinical features.

METHODS

A total of 106 children who were treated at the outpatient service or hospitalized from January 1, 2016 to May 31, 2017 were enrolled. Their nasopharyngeal swabs and venous blood samples were collected for Bordetella pertussis culture, multiple PCR and serum anti-pertussis toxin antibody detection. According to these results, the children were divided into pertussis group with 26 children and control group with 80 children, and clinical features were analyzed for both groups. E-test stripes were used to determine the sensitivity of Bordetella pertussis strains to erythromycin, azithromycin, doxycycline, levofloxacin, sulfamethoxazole/trimethoprim and amoxicillin.

RESULTS

Of the 106 children with chronic cough, 26 (24.5%) were found to have Bordetella pertussis infection. There were no significant differences in the incidence rates of typical symptoms of pertussis between the pertussis and control groups (P>0.05). E-test showed that erythromycin and azithromycin had a minimal inhibitory concentration (MIC) of >256 mg/L against five Bordetella pertussis strains, while amoxicillin had an MIC of 0.5-1 mg/L.

CONCLUSIONS

The presence of Bordetella pertussis infection in children with chronic cough should be taken seriously by clinicians, and children with chronic cough and Bordetella pertussis infection may not have the typical symptoms of pertussis and are mainly manifested as chronic cough. Amoxicillin may be an alternative drug for macrolide-resistant Bordetella pertussis infection.

Association Between Third-Trimester Tdap Immunization and Neonatal Pertussis Antibody Concentration

IMPORTANCE

Immunization with tetanus, diphtheria, and acellular pertussis (Tdap) vaccine is recommended in the United States during weeks 27 through 36 of pregnancy to prevent life-threatening infant pertussis. The optimal gestation for immunization to maximize concentrations of neonatal pertussis toxin antibodies is unknown.

OBJECTIVE

To determine pertussis toxin antibody concentrations in cord blood from neonates born to women immunized and unimmunized with Tdap vaccine in pregnancy and optimal gestational age for immunization to maximize concentrations of neonatal antibodies.

DESIGN, SETTING, AND PARTICIPANTS

Prospective, observational, cohort study of term neonates in Houston, Texas (December 2013-March 2014).

EXPOSURES

Tdap immunization during weeks 27 through 36 of pregnancy or no Tdap immunization.

MAIN OUTCOMES AND MEASURES

Primary outcome was geometric mean concentrations (GMCs) of pertussis toxin antibodies in cord blood of Tdap-exposed and Tdap-unexposed neonates and proportions of Tdap-exposed and Tdap-unexposed neonates with pertussis toxin antibody concentrations of 15 IU/mL or higher, 30 IU/mL or higher, and 40 IU/mL or higher, cutoffs representing quantifiable antibodies or levels that may be protective until the infant immunization series begins. Secondary outcome was the optimal gestation for immunization to achieve maximum pertussis toxin antibodies.

RESULTS

Six hundred twenty-six pregnancies (mean maternal age, 29.7 years; 41% white, 27% Hispanic, 26% black, 5% Asian, 1% other; mean gestation, 39.4 weeks) were included. Three hundred twelve women received Tdap vaccine at a mean gestation of 31.2 weeks (range, 27.3-36.4); 314 were unimmunized. GMC of neonatal cord pertussis toxin antibodies from the Tdap-exposed group was 47.3 IU/mL (95% CI, 42.1-53.2) compared with 12.9 IU/mL (95% CI, 11.7-14.3) in the Tdap-unexposed group, for a GMC ratio of 3.6 (95% CI, 3.1-4.2; P < .001). More Tdap-exposed than Tdap-unexposed neonates had pertussis toxin antibody concentrations of 15 IU/mL or higher (86% vs 37%; difference, 49% [95% CI, 42%-55%]), 30 IU/mL or higher (72% vs 17%; difference, 55% [95% CI, 49%-61%]), and 40 IU/mL or higher (59% vs 12%; difference, 47% [95% CI, 41%-54%]); P < .001 for each analysis. GMCs of pertussis toxin antibodies were highest when Tdap vaccine was administered during weeks 27 through 30 and declined thereafter, reaching a peak at week 30 (57.3 IU/mL [95% CI, 44.0-74.6]).

CONCLUSIONS AND RELEVANCE

Immunization with Tdap vaccine during the third trimester of pregnancy, compared with no immunization, was associated with higher neonatal concentrations of pertussis toxin antibodies. Immunization early in the third trimester was associated with the highest concentrations.

Risk factors for pertussis among hospitalized children in a high HIV prevalence setting, South Africa

BACKGROUND

In low- and middle-income countries, including South Africa, the epidemiology of pertussis in relation to immunization, nutritional, and HIV status is poorly described. This article reports on risk factors in South African children hospitalized with pertussis.

METHODS

A prospective, hospital-based, sentinel surveillance programme for pertussis was conducted in Gauteng Province, South Africa. Hospitalized children (≤10 years) meeting the surveillance criteria for clinically suspected pertussis were screened and enrolled. Nasopharyngeal specimens were collected for real-time multiplex PCR and culture of Bordetella species.

RESULTS

Bordetella pertussis was detected in 6.2% (61/992) of children. Pertussis was significantly more prevalent in infants younger than 3 months (9.8%; 38/392) and in young children between the ages of 5 and 9 years (12%; 4/34) (p=0.0013). Of the 61 confirmed pertussis cases, 17 were too young for vaccination. Of the remaining 44 infants, vaccination DTP1 was administered in 73% (32/44) of pertussis-confirmed patients who were eligible, DTP2 in 50% (16/32), DTP3 in 54% (14/26), and DTP4 in 56% (5/9) of vaccine-eligible cases at 18 months of age. B. pertussis infection was less likely in children immunized at least once (5%, 32/692) than in unvaccinated children (10%, 24/230) (p=0.0001). HIV exposure and infection status were determined in 978 (99%) patients: 69% (678/978) were HIV-unexposed and uninfected and 31% (300/978) were HIV-exposed. Of these HIV-exposed patients, 218 (22%) were proven HIV-exposed and uninfected and 82 patients were HIV-infected (8.4%, 82/978). HIV prevalence was similar in pertussis-positive (6%, 5/82) and pertussis-negative (6%, 55/896) children (p=0.90). B. pertussis infection was unrelated to poor nutritional status.

CONCLUSIONS

In South Africa, B. pertussis poses a greater risk to infants who are too young for the first vaccine dose, those who are not vaccinated in a timely manner, and those who do not receive all three primary doses. HIV infection and HIV exposure were not associated with pertussis infection.

[Recent progress in clinical research on pertussis]

Pertussis is a highly contagious respiratory disease. Despite the high vaccination coverage, re-emergence of pertussis has been reported in many countries over the past two decades. With the increase in the incidence of pertussis, there has been a shift in the epidemiological features: an increased incidence of pertussis has been noted in older children and adults, who normally lack typical clinical manifestations, and who may be easily missed according to current diagnostic references for pertussis. In order to achieve better prevention and treatment of pertussis, this review article summarized the recent research progress in the epidemiology, clinical features, etiology, diagnosis, treatment, and prevention of pertussis, particularly focusing on the diagnosis of pertussis in older children and adults.

Pertussis vaccination in pregnancy

Pertussis has had a resurgence with the highest incidence and complication rates in young infants, and deaths occurring mainly at < age 3 months. Infants are infected by older individuals whose immunity has waned. Strategies such as targeted immunization of infant caregivers have had limited success. Pertussis vaccination in pregnancy may protect infants through passive and active transfer of maternal antibodies that protect the infant until the primary immunization series. Studies show vaccinating pregnant women with acellular pertussis vaccine is safe for mother and infant, immunogenic with efficient transfer of antibodies to infants, and effective in preventing pertussis in young infants. Vaccine uptake in pregnant women is sub-optimal, but provider recommendation is the most important factor in improving vaccination rates. Studies are ongoing to determine the best timing of vaccination to protect infants, and into other strategies. Vaccinating pregnant women offers hope to prevent pertussis-related morbidity and mortality in infants worldwide.

Pertussis: Microbiology, Disease, Treatment, and Prevention

Pertussis is a severe respiratory infection caused by Bordetella pertussis, and in 2008, pertussis was associated with an estimated 16 million cases and 195,000 deaths globally. Sizeable outbreaks of pertussis have been reported over the past 5 years, and disease reemergence has been the focus of international attention to develop a deeper understanding of pathogen virulence and genetic evolution of B. pertussis strains. During the past 20 years, the scientific community has recognized pertussis among adults as well as infants and children. Increased recognition that older children and adolescents are at risk for disease and may transmit B. pertussis to younger siblings has underscored the need to better understand the role of innate, humoral, and cell-mediated immunity, including the role of waning immunity. Although recognition of adult pertussis has increased in tandem with a better understanding of B. pertussis pathogenesis, pertussis in neonates and adults can manifest with atypical clinical presentations. Such disease patterns make pertussis recognition difficult and lead to delays in treatment. Ongoing research using newer tools for molecular analysis holds promise for improved understanding of pertussis epidemiology, bacterial pathogenesis, bioinformatics, and immunology. Together, these advances provide a foundation for the development of new-generation diagnostics, therapeutics, and vaccines.

Bayesian Correction of Misclassification of Pertussis in Vaccine Effectiveness Studies: How Much Does Underreporting Matter?

Diagnosis of pertussis remains a challenge, and consequently research on the risk of disease might be biased because of misclassification. We quantified this misclassification and corrected for it in a case-control study of children in Philadelphia, Pennsylvania, who were 3 months to 6 years of age and diagnosed with pertussis between 2011 and 2013. Vaccine effectiveness (VE; calculated as (1 - odds ratio) × 100) was used to describe the average reduction in reported pertussis incidence resulting from persons being up to date on pertussis-antigen containing vaccines. Bayesian techniques were used to correct for purported nondifferential misclassification by reclassifying the cases per the 2014 Council of State and Territorial Epidemiologists pertussis case definition. Naïve VE was 50% (95% confidence interval: 16%, 69%). After correcting for misclassification, VE ranged from 57% (95% credible interval: 30, 73) to 82% (95% credible interval: 43, 95), depending on the amount of underreporting of pertussis that was assumed to have occurred in the study period. Meaningful misclassification was observed in terms of false negatives detected after the incorporation of infant apnea to the 2014 case definition. Although specificity was nearly perfect, sensitivity of the case definition varied from 90% to 20%, depending on the assumption about missed cases. Knowing the degree of the underreporting is essential to the accurate evaluation of VE.

Pertussis Across the Globe: Recent Epidemiologic Trends From 2000 to 2013

Pertussis has reemerged as a problem across the world. To better understand the nature of the resurgence, we reviewed recent epidemiologic data and we report disease trends from across the world. Published epidemiologic data from January 2000 to July 2013 were obtained via PubMed searches and open-access websites. Data on vaccine coverage and reported pertussis cases from 2000 through 2012 from the 6 World Health Organization regions were also reviewed. Findings are confounded not only by the lack of systematic and comparable observations in many areas of the world but also by the cyclic nature of pertussis with peaks occurring every 3-5 years. It appears that pertussis incidence has increased in school-age children in North America and western Europe, where acellular pertussis vaccines are used, but an increase has also occurred in some countries that use whole-cell vaccines. Worldwide, pertussis remains a serious health concern, especially for infants, who bear the greatest disease burden. Factors that may contribute to the resurgence include lack of booster immunizations, low vaccine coverage, improved diagnostic methods, and genetic changes in the organism. To better understand the epidemiology of pertussis and optimize disease control, it is important to improve surveillance worldwide, irrespective of pertussis vaccine types and schedules used in each country.

Choice of measures of vaccination and estimates of risk of pediatric pertussis

BACKGROUND

Vaccination uptake at the individual level can be assessed in a variety of ways, including traditional measures of being up-to-date (UTD), measures of UTD that consider dose timing, like age-appropriate vaccination, and risk reduction from individual doses. This analysis compared methods of operationalizing vaccination uptake and corresponding risk of pertussis infection.

METHODS

City-wide case-control study of children in Philadelphia aged 3 months through 6 years, between 2001 and 2013. Multiple logistic regression was used to isolate the independent effects of each measure of vaccination uptake and the corresponding relative odds of pertussis.

RESULTS

Being UTD on vaccinations was associated with a 52% reduction in risk of pertussis (OR 0.48, 95% CI: 0.34, 0.69). Evaluation of delayed receipt of vaccine versus on-time UTD yielded similar results. There was a decrease in risk of pertussis for each additional dose received with the greatest reduction in pertussis infection observed from the first (OR 0.48, 95% CI: 0.28, 0.83) and second dose (OR 0.17, 95% CI: 0.08, 0.34). Additional doses conferred minimal additional protection in this age group.

CONCLUSION

Examining vaccination status by individual doses may offer improved predictive capacity for identifying children at risk for pertussis infection compared to the traditional UTD measure.

Evaluation of a new syringe presentation of reduced-antigen content diphtheria, tetanus, and acellular pertussis vaccine in healthy adolescents--A single blind randomized trial

Reduced-antigen-content diphtheria-tetanus-acellular pertussis (dTpa) vaccine, Boostrix™, is indicated for booster vaccination of children, adolescents and adults. The original prefilled disposable dTpa syringe presentation was recently replaced by another prefilled-syringe presentation with latex-free tip-caps and plunger-stoppers. 671 healthy adolescents aged 10–15 years who had previously received 5 or 6 previous DT(P)/dT(pa) vaccine doses, were randomized (1:1) to receive dTpa booster, injected using the new (dTpa-new) or previous syringe (dTpa-previous) presentations. Immunogenicity was assessed before and 1-month post-booster vaccination; safety/reactogenicity were assessed during 31-days post-vaccination. Non-inferiority of dTpa-new versus dTpa-previous was demonstrated for all antigens (ULs 95% CIs for GMC ratios ranged between 1.03-1.13). 1-month post-booster, immune responses were in similar ranges for all antigens with both syringe presentations. dTpa delivered using either syringe presentation was well-tolerated. These clinical results complement the technical data and support the use of the new syringe presentation to deliver the dTpa vaccine.

Immunogenicity and reactogenicity of a decennial booster dose of a combined reduced-antigen-content diphtheria-tetanus-acellular pertussis and inactivated poliovirus booster vaccine (dTpa-IPV) in healthy adults

BACKGROUND

Pertussis in adults and adolescents could be reduced by replacing traditional tetanus and diphtheria (Td) boosters with reduced-antigen-content diphtheria-tetanus-acellular pertussis (dTpa) vaccines. This study evaluated the administration of dTpa-IPV (dTpa-inactivated poliovirus) in adults ten years after they received a booster dose of either dTpa-IPV, dTpa+IPV or Td-IPV in trial NCT01277705.

METHODS

Open multicentre, phase IV study (www.clinicaltrials.govNCT01323959) in which healthy adults, who had received a previous dose of dTpa-IPV, dTpa+IPV or Td-IPV ten years earlier, received a single decennial booster dose of dTpa-IPV (Boostrix-polio, GlaxoSmithKline Vaccines). Blood samples were collected before and one month after booster vaccination. Antibody concentrations against all vaccine antigens were measured and reactogenicity and safety were assessed.

RESULTS

A total of 211 subjects (mean age 50.3 years) received vaccination of whom 201 were included in the according-to-protocol cohort for immunogenicity. Before the decennial dTpa-IPV booster, ≥71.0% subjects were seroprotected/seropositive against all vaccine antigens. One month after the booster dose, all subjects were seroprotected against tetanus and poliovirus types 2 and 3; ≥95.7% subjects were seroprotected against diphtheria and ≥98.3% against poliovirus type 1. Anti-pertussis booster responses for the various antigens were observed in ≥76.5% (pertussis toxoid; PT), ≥85.1% (filamentous haemagglutinin; FHA) and ≥63.2% (pertactin; PRN) of subjects. During the 4-day follow-up, the overall incidence of local AEs was 71.6%, 75.0% and 72.2% in dTpa-IPV, dTpa+IPV and Td-IPV groups, respectively. Pain was the most frequent solicited local adverse event (AE; ≥62.7% subjects) and fatigue the most frequent solicited general AE (≥18.5%). No serious AEs were reported during the study.

CONCLUSION

A booster dose of dTpa-IPV was immunogenic and well tolerated in adults who had received a booster dose of either dTpa-IPV, dTpa+IPV or Td-IPV, ten years previously and supports the repeated administration of dTpa-IPV.

Pertussis

Pertussis continues to be an important public-health issue. The high immunization coverage rates achieved, mainly in industrialized countries, have certainly decreased the spread of the pathogen. However, as immunity wanes, adolescents and adults play an important role in the dynamics of the infection. The surveillance system has several limitations and the underestimation of pertussis in adolescents, young adults and adults is mainly related to the atypical clinical characteristics of cases and the lack of lab confirmation. The real epidemiological impact of pertussis is not always perceived. The unavailability of comprehensive data should not hamper the adoption of active prophylactic measures designed to avoid the impact of waning immunity against pertussis. Different immunization strategies have been suggested and/or already adopted such as immunization of newborns, pre-school and school children, adolescents, adults, healthcare workers, childcare workers, pregnant women, cocoon strategy. Prevention of pertussis requires an integrated approach and the adoption of different immunization strategies, with the objective of achieving and maintaining high coverage rates.

Evaluation of amplification targets for the specific detection of Bordetella pertussis using real-time polymerase chain reaction

BACKGROUND

Bordetella pertussis infections continue to be a major public health challenge in Canada. Polymerase chain reaction (PCR) assays to detect B pertussis are typically based on the multicopy insertion sequence IS481, which offers high sensitivity but lacks species specificity.

METHODS

A novel B pertussis real-time PCR assay based on the porin gene was tested in parallel with several previously published assays that target genes such as IS481, ptx-promoter, pertactin and a putative thialase. The assays were evaluated using a reference panel of common respiratory bacteria including different Bordetella species and 107 clinical nasopharyngeal specimens. Discrepant results were confirmed by sequencing the PCR products.

RESULTS

Analytical sensitivity was highest for the assay targeting the IS481 element; however, the assay lacked specificity for B pertussis in the reference panel and in the clinical samples. False-positive results were also observed with assays targeting the ptx-promoter and pertactin genes. A PCR assay based on the thialase gene was highly specific but failed to detect all reference strains of B pertussis. However, a novel assay targeting the porin gene demonstrated high specificity for B pertussis both in the reference panel and in clinical samples and, based on sequence-confirmed results, correctly predicted all B pertussis-positive cases in clinical samples. According to Probit regression analysis, the 95% detection limit of the new assay was 4 colony forming units/reaction.

CONCLUSION

A novel porin assay for B pertussis demonstrated superior performance and may be useful for improved molecular detection of B pertussis in clinical specimens.

[Hospitalization due to whooping cough in Spain (1997-2011)]

INTRODUCTION

Pertussis incidence has increased in recent years in countries with high vaccination coverage. The aim of this study was to determine the health impact of pertussis in Spain in the period 1997-2011 in relation to hospitalizations, mortality, and associated costs.

METHODS

We retrospectively analyzed hospital discharges included in the Minimum Data Set (MDS) in Spain for the period 1997-2011, with a primary or secondary diagnosis related to pertussis. We calculated incidence rates of hospitalization for pertussis (per 100,000) per year, by age group and by Autonomous Region, along with the mortality and lethality rates.

RESULTS

A total of 8,331 hospital discharges with a diagnosis of pertussis were recorded in Spain between 1997 and 2011. The overall incidence of pertussis hospitalizations was 1.3 cases per 100,000 inhabitants. The large majority (92%) of hospitalizations occurred in children under one year of age, with an incidence of 115.2 hospitalizations per 100,000. There were 47 deaths, 37 (79%) in the group of children under 1 year and 6 (13%) in the group older than 65 years. The estimated cost of hospitalization for pertussis was 1,841 euros.

CONCLUSION

The epidemiology of severe cases of pertussis, and its clinical and economic impact, confirms the need to modify the vaccination strategies for Spain to achieve more effective control in the most vulnerable groups.

Perceptions of Tetanus-diphteria-acellular pertussis (Tdap) Vaccination among Korean Women of Childbearing Age

BACKGROUND

The number of cases of pertussis reported has increased gradually in the last decade. Pertussis vaccination is the most effective strategy for the prevention of infection. Despite the fact that young infants are at the highest risk for pertussis, the rate of tetanus-diphtheria-acellular pertussis (Tdap) vaccination is presumed to be very low among women of childbearing age in Korea. The purpose of this study was to investigate the perceptions of women of childbearing age regarding Tdap vaccination in Korea.

MATERIALS AND METHODS

Women of childbearing age, who visited the Department of Obstetrics and Gynecology at 3 University hospitals in the Seoul and Gyeonggi-do provinces of Korea, were surveyed. Individual questionnaires were administered from April to May 2012. Demographic data, Tdap vaccination history, general knowledge about pertussis, and information on factors associated with decision on vaccination were collected.

RESULTS

Of the 500 reproductive-age women enrolled, only 4 (0.8%) had received the Tdap. The most common reason for non-vaccination was the lack of awareness of pertussis and information about the Tdap. Totally, 171 (34.2%) responded that they would receive a Tdap vaccination in the future. By multivariate analysis, general confidence in the effectiveness of the vaccine (odds ratio [OR] = 1.88, 95% confidence interval [CI] 1.17 to 3.01) was indicated as an important factor for deciding whether to receive the Tdap vaccine (P < 0.01).

CONCLUSIONS

The coverage of Tdap vaccination of women of childbearing age, including pregnant women, is very low because of the lack of awareness of pertussis and the Tdap. Education of women of childbearing age about pertussis is very important to increase Tdap vaccination rates among these women, particularly during the perinatal period.

Seroprevalence of Bordetella pertussis in the Mexican population: a cross-sectional study

SUMMARY Serum samples collected during the National Health and Nutrition survey (ENSANUT 2006) were obtained from subjects aged 1-95 years (January-October 2010) and analysed to assess the seroprevalence of Bordetella pertussis (BP) in Mexico. Subjects' gender, age, geographical region and socioeconomic status were extracted from the survey and compiled into a subset database. A total of 3344 subjects (median age 29 years, range 1-95 years) were included in the analysis. Overall, BP seroprevalence was 47.4%. BP seroprevalence was significantly higher in males (53.4%, P = 0.0007) and highest in children (59.3%) decreasing with advancing age (P = 0.0008). BP seroprevalence was not significantly different between regions (P = 0.1918) and between subjects of socioeconomic status (P = 0.0808). Women, adolescents and young adults were identified as potential sources of infection to infants. Booster vaccination for adolescents and primary contacts (including mothers) for newborns and infants may provide an important public health intervention to reduce the disease burden.

Pertussis re-emergence in the post-vaccination era

BACKGROUND

Resurgence of pertussis in the post-vaccination era has been reported in Western countries. A shift of cases from school-age children to adolescents, adults and children under 1 year of age has been described in the last decade, and mortality rates in infants are still sustained. We aimed to review and discuss the possible vaccination strategies which can be adopted in order to improve the pertussis control, by searches of Pubmed, and websites of US and European Centers for Disease Control and Prevention, between 1st January 2002, and 1st March 2013.

DISCUSSION

The following vaccination strategies have been retrieved and analysed: the cocooning strategy, the immunization of pregnant women and newborns, vaccination programs for preschool children, adolescents, adults and health-care workers. Cost-effectiveness studies provide some contrasting data, mainly supporting both maternal vaccination and cocooning. Adolescent and/or adult vaccination seems to be cost-effective, however data from observational studies suggest that this vaccination strategy, used alone, leads to a reduced pertussis burden globally, but does not affect the disease incidence in infants. Moreover, substantial logistical and economic difficulties have to be overcome to vaccinate the largest number of individuals.

SUMMARY

The simultaneous use of more than one strategy, including cocooning strategy plus vaccination of adolescents and adults, seems to be the most reasonable preventive measure. The development of new highly immunogenic and efficacious pertussis vaccines continues to be a primary objective for the control of pertussis.

Estimation of household transmission rates of pertussis and the effect of cocooning vaccination strategies on infant pertussis

BACKGROUND

Despite >50 years of universal vaccination, pertussis remains the most prevalent vaccine-preventable infectious disease in developed countries. Pertussis is often mild in adults, but can run a severe course in young infants.

METHODS

Data on transmission of pertussis within households were captured in a population-based, nationwide, prospective study performed in the Netherlands between February 2006 and December 2009. We estimated the transmission rates of pertussis with a clinically confirmed infection in 140 households, using stochastic epidemic models. Parameter estimates were used to gauge the effect of vaccinating household members (cocooning) to prevent the infection in young infants.

RESULTS

Overall transmission rates in the household were high. Fathers were less susceptible than other household members (estimated relative susceptibility of fathers = 0.44 [95% confidence interval (CI) = 0.27-0.72]), whereas mothers may be more infectious to their infants than are other household members (estimated relative infectiousness of mothers = 3.9 [95% CI = 0.59-14]). Targeted vaccination of mothers would approximately halve the probability of infants' infection. Vaccination of siblings is less effective in preventing transmission within the household, but may be as effective overall because siblings more often introduce an infection in the household. Vaccination of fathers is expected to be least effective.

CONCLUSIONS

Selective vaccination of persons in households with a young infant may substantially reduce the disease burden of pertussis in infants by reducing transmission within the household.

Hospitalizations for pertussis in Italy, 1999-2009: analysis of the hospital discharge database

Even if the incidence of pertussis has greatly decreased after the adoption of immunization, it still remains a relevant cause of death in infants in their first years of life. At national level, data are usually greatly underestimated. The objective of this study was to retrospectively review the national hospital discharge form database. The national database was retrospectively searched using the International Classification of Diseases, ninth revision, Clinical Modification system. In the period 1999-2009, 7,768 hospitalizations for pertussis (primary diagnosis) have been registered: 6,971 hospitalizations and 797 day hospital admissions. The annual mean was equal to 633.6 hospitalizations and 72.4 day hospital admissions. The majority of hospitalizations (57.4 %) involved subjects <1 year of age; the mean duration of stay was about 6 days. Conclusion These data, even if restricted to hospitalizations registered at national level, confirm the epidemiological impact of pertussis and its complications in a country with a consistently high vaccination coverage rate.

Vaccine-preventable diseases and their prophylaxis

Global uptake of new vaccines shapes the epidemiology of infections, and in turn this changing epidemiology guides vaccine development. Once introduced, surveillance and monitoring of the impact of vaccines on disease and adverse events is vital for further development. This article reviews the use of vaccines as part of routine health care, vaccines that may be required for entry into a destination country, and vaccines that are recommended because of risk during travel. Considerations and advances in the vaccination of travelers are addressed.

Phenotypic and genomic analysis of hypervirulent human-associated Bordetella bronchiseptica

Background

B. bronchiseptica infections are usually associated with wild or domesticated animals, but infrequently with humans. A recent phylogenetic analysis distinguished two distinct B. bronchiseptica subpopulations, designated complexes I and IV. Complex IV isolates appear to have a bias for infecting humans; however, little is known regarding their epidemiology, virulence properties, or comparative genomics.

Results

Here we report a characterization of the virulence of human-associated complex IV B. bronchiseptica strains. In in vitro cytotoxicity assays, complex IV strains showed increased cytotoxicity in comparison to a panel of complex I strains. Some complex IV isolates were remarkably cytotoxic, resulting in LDH release levels in A549 cells that were 10- to 20-fold greater than complex I strains. In vivo, a subset of complex IV strains was found to be hypervirulent, with an increased ability to cause lethal pulmonary infections in mice. Hypercytotoxicity in vitro and hypervirulence in vivo were both dependent on the activity of the bsc T3SS and the BteA effector. To clarify differences between lineages, representative complex IV isolates were sequenced and their genomes were compared to complex I isolates. Although our analysis showed there were no genomic sequences that can be considered unique to complex IV strains, there were several loci that were predominantly found in complex IV isolates.

Conclusion

Our observations reveal a T3SS-dependent hypervirulence phenotype in human-associated complex IV isolates, highlighting the need for further studies on the epidemiology and evolutionary dynamics of this B. bronchiseptica lineage.

Increased population prevalence of low pertussis toxin antibody levels in young children preceding a record pertussis epidemic in Australia

Background

Cross-sectional serosurveys using IgG antibody to pertussis toxin (IgG-PT) are increasingly being used to estimate trends in recent infection independent of reporting biases.

Methods/Principal Findings

We compared the age-specific seroprevalence of various levels of IgG-PT in cross-sectional surveys using systematic collections of residual sera from Australian diagnostic laboratories in 1997/8, 2002 and 2007 with reference to both changes in the pertussis vaccine schedule and the epidemic cycle, as measured by disease notifications. A progressive decline in high-level (≥62.5 EU/ml) IgG-PT prevalence from 19% (95% CI 16–22%) in 1997/98 to 12% (95% CI 11–14%) in 2002 and 5% (95% CI 4–6%) in 2007 was consistent with patterns of pertussis notifications in the year prior to each collection. Concomitantly, the overall prevalence of undetectable (<5 EU/ml) levels increased from 17% (95% CI 14–20%) in 1997/98 to 38% (95% CI 36–40%) in 2007 but among children aged 1–4 years, from 25% (95% CI 17–34%) in 1997/98 to 62% (95% CI 56–68%) in 2007. This change followed withdrawal of the 18-month booster dose in 2003 and preceded record pertussis notifications from 2008 onwards.

Conclusions/Significance

Population seroprevalence of high levels of IgG-PT is accepted as a reliable indicator of pertussis disease activity over time within and between countries with varying diagnostic practices, especially in unimmunised age groups. Our novel findings suggest that increased prevalence of undetectable IgG-PT is an indicator of waning immunity useful for population level monitoring following introduction of acellular vaccines and/or schedule changes.

Clinical definitions of pertussis: Summary of a Global Pertussis Initiative roundtable meeting, February 2011

Existing clinical case definitions of pertussis are decades old and based largely on clinical presentation in infants and children, yet an increasing burden is borne by adolescents and adults who may manifest distinct signs/symptoms. Therefore, a “one-size-fits-all” clinical case definition is no longer appropriate. Seeking to improve pertussis diagnosis, the Global Pertussis Initiative (GPI) developed an algorithm that delineates the signs/symptoms of pertussis most common to 3 age groups: 0–3 months, 4 months to 9 years, and ≥10 years. These case definitions are based on clinical presentation alone, but do include recommendations on laboratory diagnostics. Until pertussis can be accurately diagnosed, its burden will remain underestimated, making the introduction of epidemiologically appropriate preventive strategies difficult. The proposed definitions are intended to be widely applicable and to encourage the expanded use of laboratory diagnostics. Determination of their utility and their sensitivity and/or specificity versus existing case definitions is required.

Immune responses in adults to revaccination with a tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine 10 years after a previous dose

BACKGROUND

Although decennial adult boosters of tetanus and diphtheria toxoids are recommended in Canada and the United States, a second dose of pertussis vaccine during adulthood is not currently recommended.

METHODS

This open-label, multicenter study compared the safety and immunogenicity of a first dose of an adult formulation of tetanus, diphtheria, and acelluar pertussis vaccine (Tdap) with a repeat dose of Tdap in adults who had received Tdap 10 years previously.

RESULTS

A total of 769 participants ranging in age from 20 to 72 years took part in this study; 92.3% of naïve and 92.7% of repeat-dose participants had at least one solicited adverse event. Injection-site pain (84.4% and 87.8%), erythema (29.7% and 23.1%), and swelling (23.3% and 20.5%), and myalgia (53.5% and 60.1%), headache (37.6% and 40.6%), malaise (29.0% and 29.4%), and fever (4.9% and 4.2%) were the most common solicited adverse events reported in the naïve and repeat-dose groups, respectively. Postvaccination antibody levels ≥0.1 IU/mL were achieved by 99.7% of the naïve-group participants and all of the repeat-dose participants for tetanus and 96.1% of the naïve group and 98.5% of the repeat-dose group for diphtheria, both meeting the predefined noninferiority criteria. For pertussis antibodies, anti-PT (89.2 EU/mL vs. 116 EU/mL) was higher in the repeat-dose group, anti-FHA (249 vs. 214) and anti-PRN (216 vs. 266) were similar, and anti-FIM (1015 vs. 779) was higher in the naïve group. Noninferiority criteria were met for all antigens except for anti-FIM.

CONCLUSION

A repeat dose of Tdap vaccine 10 years after the first dose was well tolerated and immunogenic in adults (ClinicalTrials.gov identifier: NCT00712959).