Seroprevalence of IgG antibodies against pertussis toxin in the Chinese population: A systematic review and meta-analysis.

Pertussis is a vaccine-preventable infectious disease; however, data on pertussis antibody levels in a nationwide population are still limited in China. We aimed to pool the seropositivity rates of IgG antibodies against pertussis toxin (PT-IgG) across the country. We systematically searched PubMed, Web of Science, Embase, and the China National Knowledge Infrastructure Database for studies published between January 1, 2010, and June 30, 2023. Studies reporting the seroprevalence of PT-IgG among a healthy Chinese population were included. Pooled estimates were obtained using random-effects meta-analyzes. The meta-analysis included 39 studies (47,778 participants) reporting anti-PT IgG seropositivity rates. The pooled rate for all ages was 7.06% (95% CI, 5.50%-9.07%). Subgroup analyzes showed rates ranging from 6.36% to 12.50% across different age groups. This meta-analysis indicated a low anti-PT IgG seropositivity rate in the Chinese population, particularly among school-aged children and young adults. This finding underscores the urgent need to refine immunization strategies.

Seroepidemiology of pertussis in Huzhou: A population-based, cross-sectional study.

PURPOSE: The resurgence of pertussis has occurred around the world. However, the epidemiological profiles of pertussis cannot be well understood by current diseases surveillance. This study was designed to understand the seroepidemiological characteristics of pertussis infection in the general population of Huzhou City, evaluate the prevalence infection of pertussis in the population, and offer insights to inform adjustments in pertussis prevention and control strategies. METHODS: From September to October 2023, a cross-sectional serosurvey was conducted in Huzhou City, involving 1015 permanent residents. Serum samples were collected from the study subjects, and pertussis toxin IgG antibodies (Anti-PT-IgG) were quantitatively measured using enzyme-linked immunosorbent assay (ELISA). The analysis included the geometric mean concentration (GMC) of Anti-PT-IgG, rates of GMC≥40IU/mL, ≥100IU/mL, and <5IU/mL. Stratified comparisons were made based on age, vaccination history, and human categories. RESULTS: Among the 1015 surveyed individuals, the geometric mean concentration (GMC) of Anti-PT-IgG was 10.52 (95% CI: 9.96-11.11) IU/mL, with a recent infection rate of 1.58%, a serum positivity rate of 11.43%, and a proportion with <5IU/mL of 40.49%. Among 357 children with clear vaccination history, susceptibility decreased with an increasing number of vaccine doses (Z = -6.793, P < 0.001). The concentration of Anti-PT-IgG exhibited a significant post-vaccination decline over time (Z = -5.143, P < 0.001). In women of childbearing age, the GMC of Anti-PT-IgG was 7.71 (95% CI: 6.90-8.62) IU/mL, with no significant difference in susceptibility among different age groups (χ2 = 0.545, P = 0.909). The annual pertussis infection rate in individuals aged ≥3 years was 9321 (95%CI: 3336-16039) per 100,000, with peak infection rates in the 20-29, 40-49, and 5-9 age groups at 34363 (95%CI: 6327-66918) per 100,000, 22307.72 (95%CI: 1380-47442) per 100,000, and 18020(95%CI: 1093-37266) per 100,000, respectively. CONCLUSIONS: In 2023, the actual pertussis infection rate in the population of Huzhou City was relatively high. Vaccine-induced antibodies exhibit a rapid decay, and the estimated serum infection rate increases rapidly from post-school age, peaking in the 20-29 age group. It is recommended to enhance pertussis monitoring in adolescents and adults and refine vaccine immunization strategies.

Transplacental transfer of maternal antibodies following immunization with recombinant pertussis vaccines during pregnancy: Real-world evidence.

AIM/OBJECTIVE: This study investigates placental antibody transfer following recombinant pertussis vaccination in pregnancy in a real-world setting. METHODS: This postmarketing observational study recruited pregnant women vaccinated with monovalent recombinant acellular pertussis (aP) vaccine (aPgen; n = 199) or combined to tetanus-diphtheria (TdaPgen; n = 200), or Td-vaccine only (n = 54). Pregnancy, delivery, and neonatal outcomes were assessed. Cord blood was collected postdelivery and pertussis toxin (PT)-IgG, filamentous hemagglutinin (FHA)-IgG, and PT-neutralizing antibodies (PT-Nab) were assessed. RESULTS: No adverse pregnancy, delivery, or neonatal outcomes attributed to aPgen, TdaPgen, or Td vaccination were reported. High anti-PT antibody levels were detected in cord samples from women vaccinated with aPgen (geometric mean concentration [GMC] PT-IgG 206.1 IU/ml, 95% confidence intervals [CI]: 164.3-258.6; geometric mean titer [GMT] PT-Nab 105.3 IU/ml, 95% CI: 81.7-135.8) or TdaPgen (GMC PT-IgG 153.1 IU/ml, 95% CI: 129.1-181.5; GMT PT-Nab 81.5 IU/ml, 95% CI: 66.4-100.0). In the Td-only group, anti-PT antibodies were low (GMC PT-IgG 6.5 IU/ml, 95% CI: 4.9-8.8; GMT PT-Nab 3.8 IU/ml, 95% CI: 2.8-5.1). The same was found for FHA-IgG. Recombinant pertussis vaccination at <27 or 27-36 weeks gestation induced similar cord pertussis antibody levels. CONCLUSION: This first real-world study confirms that recombinant pertussis vaccination in the second or third trimester of pregnancy results in high levels of passive immunity in infants. Thai Clinical Trial Registry: TCTR20200528006.

Comparison of Bordetella pertussis Antibody Levels in Pregnant Women and Umbilical Cord Blood: A Multicenter Study.

BACKGROUND: In countries where pertussis vaccination is not administered during pregnancy, the determination of pertussis antibody levels in pregnant women is very important in terms of knowing the current seroepidemiology and potential strategies for immunizations. METHODS: We included 396 pregnant women who were admitted to 4 different obstetrics and gynecology clinics. Anti-Bordetella pertussis toxin (PT) IgG and anti-Bordetella pertussis filamentous hemagglutinin IgG levels in maternal and cord blood pairs were determined by the ELISA method. RESULTS: Venous blood serum anti-PT level was below 5 IU/mL in 58.8%, 5-40 IU/mL in 34.8%, 40-100 IU/mL in 5.1% and >100 IU/mL in 1.3% of pregnant women. Cord blood serum anti-PT level was below 5 IU/mL in 47.7%, 5-40 IU/mL in 44.5%, 40-100 IU/mL in 6.8% and >100 IU/mL in 1% of pregnant women. In our study, the anti-PT level was found below 40 IU/mL in 93.6% of pregnant women and 92.2% of cord blood. Our study found the anti-filamentous hemagglutinin level below 40 IU/mL in 81% of pregnant women and 66.2% of cord blood. CONCLUSIONS: Although it is known that pertussis causes serious morbidity and mortality in young infants all over the world and that the most effective and reliable way to prevent it is vaccination of pregnant women, it is a remarkable contradiction that pertussis vaccination rates and therefore seropositivity rates in pregnant women are very low.

Assessing the In Vivo Effectiveness of Cationic Lipid Nanoparticles with a Triple Adjuvant for Intranasal Vaccination against the Respiratory Pathogen Bordetella pertussis.

Continuous outbreaks of pertussis around the world suggest inadequate immune protection in infants and weakened immune responses induced over time by the acellular pertussis vaccine. Vaccine adjuvants provide a means to improve vaccine immunogenicity and support long-term adaptive immunity against pertussis. An acellular pertussis vaccine was prepared with pertactin, pertussis toxin, and fimbriae 2/3 antigens combined with a triple-adjuvant system consisting of innate defense regulator peptide IDR 1002, a Toll-like receptor-3 agonist poly(I:C), and a polyphosphazene in a fixed combination. The vaccine was delivered intranasally in a cationic lipid nanoparticle formulation fabricated by simple admixture and two schema for addition of antigens (LT-A, antigens associated outside of L-TriAdj, and LAT, antigens associated inside of L-TriAdj) to optimize particle size and cationic surface charge. In the former, antigens were associated with the lipidic formulation of the triple adjuvant by electrostatic attraction. In the latter, the antigens resided in the interior of the lipid nanoparticle. Two dose levels of antigens were used with adjuvant comprised of the triple adjuvant with or without the lipid nanoparticle carrier. Formulation of vaccines with the triple adjuvant stimulated systemic and mucosal immune responses. The lipid nanoparticle vaccines favored a Th1 type of response with higher IgG2a and IgA serum antibody titers particularly for pertussis toxin and pertactin formulated at the 5 µg dose level in the admixed formulation. Additionally, the lipid nanoparticle vaccines resulted in high nasal SIgA antibodies and an early (4 weeks post vaccination) response after a single vaccination dose. The LT-A nanoparticles trended toward higher titers of serum antibodies compared to LAT. The cationic lipid-based vaccine nanoparticles formulated with a triple adjuvant showed encouraging results as a potential formulation for intranasally administered pertussis vaccines.

The History of Pertussis Toxin.

Besides the typical whooping cough syndrome, infection with Bordetella pertussis or immunization with whole-cell vaccines can result in a wide variety of physiological manifestations, including leukocytosis, hyper-insulinemia, and histamine sensitization, as well as protection against disease. Initially believed to be associated with different molecular entities, decades of research have provided the demonstration that these activities are all due to a single molecule today referred to as pertussis toxin. The three-dimensional structure and molecular mechanisms of pertussis toxin action, as well as its role in protective immunity have been uncovered in the last 50 years. In this article, we review the history of pertussis toxin, including the paradigm shift that occurred in the 1980s which established the pertussis toxin as a single molecule. We describe the role molecular biology played in the understanding of pertussis toxin action, its role as a molecular tool in cell biology and as a protective antigen in acellular pertussis vaccines and possibly new-generation vaccines, as well as potential therapeutical applications.

PTX Instructs the Development of Lung-Resident Memory T Cells in Bordetella pertussis Infected Mice.

Whooping cough is a severe, highly contagious disease of the human respiratory tract, caused by Bordetellapertussis. The pathogenicity requires several virulence factors, including pertussis toxin (PTX), a key component of current available vaccines. Current vaccines do not induce mucosal immunity. Tissue-resident memory T cells (Trm) are among the first lines of defense against invading pathogens and are involved in long-term protection. However, the factors involved in Trm establishment remain unknown. Comparing two B.pertussis strains expressing PTX (WT) or not (ΔPTX), we show that the toxin is required to generate both lung CD4+ and CD8+ Trm. Co-administering purified PTX with ΔPTX is sufficient to generate these Trm subsets. Importantly, adoptive transfer of lung CD4+ or CD8+ Trm conferred protection against B. pertussis in naïve mice. Taken together, our data demonstrate for the first time a critical role for PTX in the induction of mucosal long-term protection against B. pertussis.

Evaluation of Anti-PT Antibody Response after Pertussis Vaccination and Infection: The Importance of Both Quantity and Quality.

Pertussis toxin (PT) is considered the main virulence factor causing whooping cough or pertussis. The protein is widely studied and its composition was revealed and sequenced already during the 1980s. The human immune system creates a good response against PT when measured in quantity. However, the serum anti-PT antibodies wane rapidly, and only a small amount of these antibodies are found a few years after vaccination/infection. Therefore, multiple approaches to study the functionality (quality) of these antibodies, e.g., avidity, neutralizing capacity, and epitope specificity, have been investigated. In addition, the long-term B cell memory (Bmem) to PT is crucial for good protection throughout life. In this review, we summarize the findings from functional PT antibody and Bmem studies. These results are discussed in line with the quantity of serum anti-PT antibodies. PT neutralizing antibodies and anti-PT antibodies with proper avidity are crucial for good protection against the disease, and certain epitopes have been identified to have multiple functions in the protection. Although PT-specific Bmem responses are detectable at least five years after vaccination, long-term surveillance is lacking. Variation of the natural boosting of circulating Bordetella pertussis in communities is an important confounding factor in these memory studies.

Vascular and immunopathological role of Asymmetric Dimethylarginine (ADMA) in Experimental Autoimmune Encephalomyelitis.

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase (NOS) inhibitor/uncoupler inducing vascular pathology. Vascular pathology is an important factor for the development and progression of CNS pathology of MS, yet the role of ADMA in MS remains elusive. Patients with multiple sclerosis (MS) are reported to have elevated blood levels of ADMA, and mice with experimental autoimmune encephalomyelitis (EAE, an animal model of MS) generated by auto-immunization of myelin oligodendrocyte glycoprotein (MOG) and blood-brain barrier (BBB) disruption by pertussis toxin also had increased blood ADMA levels in parallel with induction of clinical disease. To explore the role of ADMA in EAE pathogenesis, EAE mice were treated with a daily dose of ADMA. It is of special interest that ADMA treatment enhanced the BBB disruption in EAE mice and exacerbated the clinical and CNS disease of EAE. ADMA treatment also induced the BBB disruption and EAE disease in MOG-immunized mice even without pertussis toxin treatment, suggesting the role of ADMA in BBB dysfunction in EAE. T-cell polarization studies also documented that ADMA treatment promotes TH 1- and TH 17-mediated immune responses but without affecting Treg-mediated immune response in EAE mice as well as in in vitro T-cell culture. Taken together, these data, for the first time, document the vascular and immunopathogenic roles of ADMA in EAE, thus pointing to the potential of ADMA-mediated mechanism as a new target of potential therapy for MS.

Designing a New Multi-Epitope Pertussis Vaccine with Highly Population Coverage Based on a Novel Sequence and Structural Filtration Algorithm.

Pertussis vaccine is produced from physicochemically inactivated toxin for many years. Recent advancements in immunoinformatics [N. Tomar and R. K. De, "Immunoinformatics: an integrated scenario," Immunology, vol. 131, no. 2, pp. 153-168, 2010] and structural bioinformatics can provide a new multidisciplinary approach to overcome the concerns including unwanted antibodies and incomplete population coverage. In this study we focused on solving the challenging issues by designing a multi-epitope vaccine (MEV) using rational bioinformatics analyses. The frequencies of All HLA DP, DQ, and DR alleles were evaluated in almost all countries. Strong binder surface epitopes on the pertussis toxin were selected based on our novel filtration strategy. Finally, the population coverage of MEV was determined in the candidate country. Filtration steps yielded 312 strong binder epitopes. Finally, 8 surface strong binder epitopes were selected as candidate epitopes. The population coverage of the MEV in France and the world was 98 and 100 percent, respectively. Our algorithm successfully filtered many unwanted strong binder epitopes. Considering the HLA type of all individuals in a country, we theoretically provided the maximum chance to all humans to be vaccinated efficiently. Application of a MEV would be led to production of highly efficient target specific antibodies, significant reduction of unwanted antibodies, and avoid possible raising of auto-antibodies as well.

Safety and immunogenicity of the epicutaneous reactivation of pertussis toxin immunity in healthy adults: a phase I, randomized, double-blind, placebo-controlled trial.

OBJECTIVES: Protection induced by acellular vaccines can be short, requiring novel immunization strategies. Objectives of this study were to evaluate safety and capacity of a recombinant pertussis toxin (PTgen) -coated Viaskin® epicutaneous patch to recall memory responses in healthy adults. METHODS: This double-blind, placebo-controlled randomized trial (Phase I) assessed the safety and immunogenicity of PTgen administered on days 0 and 14 to healthy adults using Viaskin® patches applied directly or after epidermal laser-based skin preparation. Patch administration was followed by Boostrix®dTpa on day 42. Antibodies were assessed at days 0, 14, 28, 42 and 70. RESULTS: Among 102 volunteers enrolled, 80 received Viaskin-PT (Viaskin-PT 25 µg (n = 25), Viaskin-PT 50 µg (n = 25), laser + Viaskin-PT 25 µg (n = 5), laser + Viaskin-PT 50 µg (n = 25)), Viaskin-placebo (n = 10) or laser + Viaskin-placebo (n = 2). Incidence of adverse events was similar across groups (any local event: 21/25 (84.0%), 24/25 (96.0%), 4/5 (80.0%), 24/25 (96.0%), 8/10 (80.0%), 10/12 (83.0%), respectively). Direct application induced no detectable response. On day 42, PT-IgG geometric mean concentrations were significantly higher following laser + Viaskin-PT 25 µg and 50 µg (139.87 (95% CI 87.30-224.10) and 121.76 (95% CI 95.04-156.00), respectively), than laser + Viaskin-placebo (59.49, 95% CI 39.37-89.90). Seroresponse rates were higher following laser + Viaskin-PT 25 µg (4/5 (80.0%), 95% CI 28.4-99.5) and 50 µg (22/25 (88.0%), 95% CI 68.8-97.5) than laser + Viaskin-placebo (0/12 (0.0%), 95% CI 0.0-26.5). CONCLUSIONS: Viaskin-PT applied after laser-based epidermal skin preparation showed encouraging safety and immunogenicity results: anti-PT booster responses were not inferior to those elicited by Boostrix®dTpa. This study is registered at ClinicalTrials.gov (NCT03035370) and was funded by DBV Technologies.

Establishment of Ph. Eur. Bordetella pertussis mouse antiserum Biological Reference Preparation batches 2, 3 and 4.

A project aimed at establishing replacement batches for the European Pharmacopoeia (Ph. Eur.) Biological Reference Preparation (BRP) Bordetella (B.) pertussis mouse antiserum was started in 2013 under the aegis of the Biological Standardisation Programme (BSP) of the European Directorate for the Quality of Medicines & HealthCare (EDQM). This BRP is used for the immunogenicity assay in mice to assess the potency of acellular pertussis (aP) vaccines as described in Ph. Eur. general method 2.7.16. Assay of pertussis vaccine (acellular). In a preliminary phase of the project (referred to herein as BSP129 phase 1) a hyper-immune serum pool was produced in mice using a combined aP vaccine as immunogen. This pool was used to generate 3 freeze-dried candidate (c) B. pertussis anti-mouse serum BRP batches (cBRP2, cBRP3 and cBRP4). After the pre-qualification that showed their suitability as candidate batches, an international collaborative study (BSP129 phase 2) was carried out in order to standardise these 3 batches against the current BRP1 in terms of anti-PT, -FHA, -PRN and -FIM2/3 antibody contents. For the sake of continuity with the standardisation of BRP1, the corresponding WHO standard (1RR 97/642) was introduced as a second reference for the calibration of the 3 candidate BRPs. Eleven laboratories took part in phase 2. Ten of them performed the ELISA method they use routinely for aP vaccine batch release and one laboratory performed the Multiplex Immunoassay (MIA) as an alternative test. Four participants titrated the antibodies against all 5 pertussis antigens, 5 participants determined the antibody content against 3 antigens (PT, FHA, PRN), one participant titrated the antibodies against PT and FHA antigens and one laboratory determined the antibody content for the PT antigen only. Details of all ELISA methods used were analysed to evaluate their impact on the calibration of the cBRPs. The variability of the results in relation to the nature and methodology of the tests appeared rather limited. Discrepant titres of cBRPs were measured depending on the reference used: the use of the 1RR induced an overestimation (in 8 out of 11 laboratories) and a large inter-laboratory variation in the calculated titres. Regardless of the reference used, equivalency between the calculated titres of cBRP2 and cBRP3 was observed, whilst cBRP4 had systematically lower titres for all antibodies against the 5 acellular pertussis vaccine components. Based on these observations, it was decided to establish the candidate BRP batches against BRP1 and to assign the following potencies based on the mean values determined through centrally calculated results of the calibration assays performed by ELISA in BSP129 phase 2: For cBRP2 and cBRP3 Anti-pertussis toxin: 37 ELISA Units (ELU) per vial Anti-filamentous haemagglutinin: 114 ELU per vial Anti-pertactin: 44 ELU per vial Anti-fimbrial agglutinogens (FIM2/3): 25 ELU per vial For cBRP4 Anti-pertussis toxin: 32 ELU per vial Anti-filamentous haemagglutinin: 98 ELU per vial Anti-pertactin 38 ELU per vial Anti-fimbrial agglutinogens (FIM2/3):23 ELU per vial In February 2018, BRP2, BRP3 and BRP4 were adopted by correspondence by the Ph. Eur. Commission.

An Investigation of Japanese Neonatal and Maternal Antibody Status against Pertussis.

To clarify the pertussis immune status of the Japanese population, we investigated levels of serum pertussis toxin (PT)-specific immunoglobulin G (IgG) antibody in infants and mothers between April 2016 and March 2018. A total of 206 infants (n = 22, < 32 weeks of gestational age [wGA]; n = 70, 32-36 wGA; n = 114, ≥ 37 wGA) and 170 mothers were enrolled. The maternal seroprevalence and antibody geometric mean titer (GMT) were 52.4% and 10.7 EU/mL, respectively. The antibody GMT, seroprevalence, and mean ratio of infant to maternal antibody titers of infants at < 32 wGA were 3.2 EU/mL, 13.6%, and 42.5%, respectively, and were significantly lower than those of infants at 32-36 wGA (9.7 EU/mL, 54.3%, and 110.2%) and infants at ≥ 37 wGA (12.1 EU/mL, 57.9%, and 112.6%). Of the 21 infants who underwent a second examination, five were positive in the first examination. Of those five, the GMT for PT had decreased by an average of 52.6% at 4.3- week intervals. In the second examination, two infants were seropositive. Approximately half of the mothers and infants were negative for anti-PT antibody. Thus, new vaccination strategies, such as the vaccination of pregnant women, are needed to prevent pertussis infection in early infancy.

Maraviroc attenuates the pathogenesis of experimental autoimmune encephalitis.

It has been shown that the blockade of chemokine receptor type 5 can dampen inflammatory reaction within the central nervous system (CNS). In the present study, we utilized maraviroc, a potent antagonist o CCR5, to examine whether this drug can mitigate neuroinflammation in the spinal cord of mice induced by experimental autoimmune encephalitis (EAE), considered a murine model of multiple sclerosis (MS). For this aim, mice were immunized with myelin oligodendrocyte glycoprotein 35-55 (MOG35-55), followed by pertussis toxin to induce paralysis in EAE mice. The animals intraperitoneally received various doses of maraviroc (5, 25, and 50 mg/kg body weight) when the early clinical signs of EAE appeared. The results demonstrated that the administration of maraviroc led to a marked decrease in the clinical score and improvement in behavioral motor functions. Moreover, our finding indicated that the administration of maraviroc significantly attenuates the infiltration of inflammatory cells to the spinal cord, microgliosis, astrogliosis, pro-inflammatory cytokines, and cell death in EAE mice. The flow cytometry data indicated that a decreased number of CD4+ and CD8+ T cells in the peripheral blood of mice with EAE without affecting the number of T regulatory cells (CD4 + CD25+ forkhead box protein 3+). Finally, it seems that maraviroc is well-tolerated, and targeting CCR5 could open up a new horizon in the treatment of MS.

Neutralization of pertussis toxin by a single antibody prevents clinical pertussis in neonatal baboons.

Pertussis continues to cause considerable infant mortality world-wide, which could be addressed in part by passive immunization strategies. Antibody hu1B7 is a candidate therapeutic that potently neutralizes pertussis toxin in vitro, prevents leukocytosis in mice and treats established disease in weanling baboons as part of an antibody cocktail. Here, we evaluated the potential for hu1B7 and an extended half-life hu1B7 variant to prevent death, leukocytosis and other clinical symptoms in a newborn baboon model that mimics many aspects of human disease. We administered a single antibody dose to newborn baboons five weeks prior to experimental infection. While all animals were heavily colonized with Bordetella pertussis, prophylaxed animals showed significantly greater survival (P < 0.005), delayed and suppressed leukocytosis (P < 0.01) and enhanced clinical outcomes, including coughing (P < 0.01), as compared to controls. Together, this work demonstrates that a single neutralizing anti-PTx antibody is sufficient to prevent clinical pertussis symptoms.

Pertussis in infants, in their mothers and other contacts in Casablanca, Morocco.

BACKGROUND: In recent decades, there has been a marked increase in the number of reported cases of pertussis around the world, and pertussis continues to be a frequently occurring disease despite an effective childhood vaccination. This study aims to determine the role of household contacts of children diagnosed with pertussis in Casablanca Morocco. METHODS: From November 2015 to October 2017, children suspected of whooping cough that consulted Ibn Rochd University hospital at Casablanca with their household contacts were enrolled in the study. Nasopharyngeal (NP) samples of the suspected children were analyzed by culture and RT-PCR. For the household contacts, NP and blood samples were collected and analyzed by RT-PCR and specific detection of pertussis toxin antibodies by ELISA, respectively. RESULTS: During the study period, the survey was carried out on 128 infants hospitalized for pertussis suspicion and their families (N = 140). B. pertussis DNA was specifically detected in 73 (57%) samples, coexistence of B. pertussis and B. parapertussis DNA in 3 (2.3%) samples, coexistence of B. pertussis and B. holmesii DNA in 10 (7.81%) and only one (0.78%) sample was IS 481 RT-PCR positive without the possibility of determining the Bordetella species with the diagnostic tools used. Confirmations of Pertussis infection in household contacts by culture, RT- PCR and serology were 10, 46 and 39%, respectively. B. pertussis DNA was confirmed in the infants as well in their mothers in 38% of the cases. Co detection of B. pertussis and B. parapertussis DNA in 2% and co-detection of B. pertussis and B. holmesii DNA in 4%. B. holmesii DNA alone was detected in 5 NP samples of index cases and their mothers. CONCLUSIONS: The results of this study confirm that B. pertussis is still circulating in children and adults, and were likely a source of pertussis contamination in infants still not vaccinated. The use of RT-PCR specific for B. pertussis in the diagnosis of adults is less sensitive and should be associated with serologic tests to improve diagnosis of pertussis and contributes to preventing transmission of the disease in infants.

Assessment of IgA anti-PT and IgG anti-ACT reflex testing to improve Bordetella pertussis serodiagnosis in recently vaccinated subjects.

OBJECTIVES: Quantifying IgG antibodies to pertussis toxin (PT) is the most specific and sensitive method for the serodiagnosis of a Bordetella pertussis infection. Since PT is a component of acellular pertussis vaccines, anti-PT IgG is also induced by vaccination, precluding pertussis serodiagnosis based exclusively on anti-PT IgG in recently vaccinated subjects. Here, we aim to identify additional B. pertussis-specific serological markers that can discriminate between infection and recent vaccination. METHODS: The clinical usefulness of measuring IgA directed to the vaccine antigen PT and IgG directed to non-vaccine antigens (Fim2/3, LPS, ACT, CatACT) was evaluated in nine well characterized subject groups, aged 10-89 years (n = 390). Serum anti-PT IgG levels (>125 IU/mL) served as an indicator for a recent B. pertussis infection. Comparing symptomatic pertussis-infected subjects (n = 140) with recently vaccinated, non-infected subjects (n = 100) revealed the optimal cut-off, accuracy, sensitivity and specificity for each single parameter. RESULTS: For pertussis diagnosis in recently vaccinated subjects, the measurement of anti-PT IgA (cut-off 15 IU/mL) and anti-ACT IgG (cut-off 15 U/mL) resulted in accuracies of 95% (91.5-97.1) and 87.5% (82.7-91.1), sensitivities of 92.9% (87.4-96.0) and 83.6% (76.5-88.8) and specificities of 98% (93.0-99.4) and 93% (86.3-96.6), respectively. Comparing anti-PT IgA levels between the youngest (10-19 years, n = 38) and oldest (70-89 years, n = 17) age groups revealed an age-dependent increase in antibody levels in pertussis-infected subjects (p < 0.0001). CONCLUSIONS: Reflex testing of anti-PT IgA and anti-ACT IgG improves pertussis serodiagnosis in recently vaccinated symptomatic subjects with elevated anti-PT IgG levels. Furthermore, both markers can discriminate between vaccination and recent infection in pertussis serosurveillance studies.

The Effect of Timing of Tetanus-Diphtheria-Acellular Pertussis Vaccine Administration in Pregnancy on the Avidity of Pertussis Antibodies.

Background: Optimal timing of gestational tetanus-diphtheria-acellular pertussis (Tdap) vaccination is not well-defined. No well-established specific anti-pertussis antibody level correlates with protection, suggesting the importance of antibody quality such as avidity. We aimed to determine the effect of timing of vaccination with Tdap in pregnancy on the avidity of cord anti-pertussis toxin (PT) immunoglobulin G (IgG). Methods: Prospective study of newborns in a tertiary hospital (Melbourne, Australia) born to women vaccinated with Tdap in pregnancy. Ammonium thiocyanate was used as a bond-breaking agent to measure the avidity of anti-PT IgG using concentrations between 0.25 M (to measure low avidity antibodies) and 3 M (to measure very high avidity antibodies). Anti-PT IgG levels achieved at each ammonium thiocyanate concentration in cord samples of women vaccinated during 28-32 weeks gestation (WG) vs. 33-36 WG, and women vaccinated 5-12 vs. 1-4 weeks prior to delivery were compared using t-tests. Results: Newborns of women vaccinated with Tdap during 28-32 WG (n = 43) had statistically significant higher concentrations of medium and high avidity anti-PT IgG compared with newborns of women vaccinated during 33-36 WG (n = 47), 11.6 IU/ml (95% CI, 8.8-15.2) IU/ml vs. 6.7 IU/ml (95% CI, 5.2-8.6) and 10.1 IU/ml (95% CI, 7.4-13.8) vs. 5.7 (95% CI, 3.6-8.9) IU/ml (p = 0.007 and p = 0.035), respectively. Newborns of women vaccinated 5-12 weeks before delivery (n = 64) had statistically significant higher concentrations of high and very high avidity anti-PT IgG compared with newborns of women vaccinated within 4 weeks before delivery (n = 25), 10.3 IU/mL (95% CI, 7.9-13.4) vs. 3.3 IU/mL (95% CI, 1.7-6.4), 12.6 IU/mL (95% CI, 9.4-16.9) vs. 4.3 IU/mL (95% CI, 2.2-8.5) (all p < 0.03), respectively. Conclusions: Quantification of levels of anti-PT IgG with different avidities demonstrated that pertussis vaccination 5-12 weeks before delivery was associated with higher anti-PT IgG avidity compared with vaccination within 4 weeks before delivery. Pertussis vaccination during 28-32 WG was associated with higher anti-PT IgG avidity compared with vaccination during 33-36 WG, supporting vaccination at 28-32 over 33-36 WG for optimal protection against pertussis in infancy.

Pertussis Toxin: A Key Component in Pertussis Vaccines?

B. pertussis is a human-specific pathogen and the causative agent of whooping cough. The ongoing resurgence in pertussis incidence in high income countries is likely due to faster waning of immunity and increased asymptomatic colonization in individuals vaccinated with acellular pertussis (aP) vaccine relative whole-cell pertussis (wP)-vaccinated individuals. This has renewed interest in developing more effective vaccines and treatments and, in support of these efforts, defining pertussis vaccine correlates of protection and the role of vaccine antigens and toxins in disease. Pertussis and its toxins have been investigated by scientists for over a century, yet we still do not have a clear understanding of how pertussis toxin (PT) contributes to disease symptomology or how anti-PT immune responses confer protection. This review covers PT's role in disease and evidence for its protective role in vaccines. Clinical data suggest that PT is a defining and essential toxin for B. pertussis pathogenesis and, when formulated into a vaccine, can prevent disease. Additional studies are required to further elucidate the role of PT in disease and vaccine-mediated protection, to inform the development of more effective treatments and vaccines.

Seroprevalence of Bordetella pertussis toxin antibodies in children and adolescents in Tunis, Tunisia.

Pertussis remains a public health concern in most countries. This cross-sectional study aims to investigate the distribution of pertussis toxin antibodies (anti-PT IgG) in Tunisian children and adolescents aged 3-18 years, to define optimal age for booster vaccination. Anti-PT IgG concentrations of enrolled participants were measured using commercial enzyme-linked immunosorbent assay. Concentrations were classified as: indicative of current/recent infection if ⩾100 IU/ml, indicative of recent exposure to Bordetella pertussis within the last year if 40-100 IU/ml and less likely revealing a recent exposure to B. pertussis if <40 IU/ml. Between March and June 2018, a total of 304 participants (mean age: 9.3 years) were included in this study. Overall, 12.8% (95% confidence interval (CI) 9.1%-16.6%) were seropositive (IgG levels ⩾40 IU/ml). Among them, 14.7% (95% CI 2.3%-23.3%) had levels indicative of a current/recent infection. The multivariate Poisson regression analysis suggested associations between female gender, as well as age group 13-18 years and 3-5 years and higher anti-PT IgG concentrations. Our results are consistent with the notion that vaccine-induced immunity decline, as well as circulation of pertussis among school children and adolescents enables them to be reservoirs of infection and disease transmission to vulnerable infants. Booster dose of acellular pertussis vaccine for school entrants is therefore recommended.