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Rathod V, Kadam L, Gautam M, Gumma PD, Marke K, Asokanathan C, Douglas-Bardsley A, Hassell L, Bhandare S, Gupta S, Parekh S, Pujari P, Rao H, Sharma H, Shaligram U, Gairola S. Multiplexed bead-based assay for the simultaneous quantification of human serum IgG antibodies to tetanus, diphtheria, pertussis toxin, filamentous hemagglutinin, and pertactin. Front Immunol 2023; 14:1190404. [PMID: 37342321 PMCID: PMC10278353 DOI: 10.3389/fimmu.2023.1190404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 05/02/2023] [Indexed: 06/22/2023] Open
Abstract
Background Luminex bead-based assays offer multiplexing to test antibodies against multiple antigens simultaneously; however, this requires validation using internationally certified reference standards. Therefore, there is an urgent need to characterize existing reference standards for the standardization of multiplex immunoassays (MIAs). Here, we report the development and validation of an MIA for the simultaneous estimation of levels of human serum immunoglobulin G (IgG) antibodies for pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (PRN), diphtheria toxoid (DT), and tetanus toxoid (TT). Methods The MIA was assessed using a panel of human serum samples and WHO reference standards. The WHO reference standards were also studied for suitability in the MIA. Purified antigens (PT, FHA, PRN, DT, and TT) were coupled to the spectrally unique magnetic carboxylated microspheres. The method was validated in accordance with the United States Food and Drug Administration (US FDA), European Medicines Agency (EMA), and the International Committee of Harmonization Multidisciplinary (ICH M10) guidelines, and parameters such as precision, accuracy, dilutional linearity, assay range, robustness, and stability were assessed. Method agreements with commercially available IgG enzyme-linked immunosorbent assay (ELISA) assays were also evaluated. In addition, the study assessed the level of correlation between the IgG levels estimated by the MIA and the cell-based neutralizing antibody assays for PT and DT. Results We identified that an equimix of WHO international standards (i.e., 06/142, 10/262, and TE-3) afforded the best dynamic range for all the antigens in the MIA. For all five antigens, we observed that the back-fitted recoveries using the four-parameter logistic (4-PL) regression fits ranged between 80% and 120% for all calibration levels, and the percentage coefficient of variation (% CV) was < 20%. In addition, the difference in mean fluorescence intensity (MFI) between the monoplex and multiplex format was < 10% for each antigen, indicating no crosstalk among the beads. The MIA also showed good agreement with conventional and commercially available assays, and a positive correlation (> 0.75) with toxin neutralization assays for PT and DT was observed. Conclusion The MIA that was calibrated in accordance with WHO reference standards demonstrated increased sensitivity, reproducibility, and high throughput capabilities, allowing for the design of robust studies that evaluate both natural and vaccine-induced immunity.
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Affiliation(s)
- Vishal Rathod
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Laxmikant Kadam
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Manish Gautam
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Prabhu Dasu Gumma
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Kevin Marke
- Science, Research and Innovation, Medicines, and Healthcare Products Regulatory Agency, South Mimms, United Kingdom
| | - Cathy Asokanathan
- Science, Research and Innovation, Medicines, and Healthcare Products Regulatory Agency, South Mimms, United Kingdom
| | - Alex Douglas-Bardsley
- Science, Research and Innovation, Medicines, and Healthcare Products Regulatory Agency, South Mimms, United Kingdom
| | - Laura Hassell
- Science, Research and Innovation, Medicines, and Healthcare Products Regulatory Agency, South Mimms, United Kingdom
| | - Sachin Bhandare
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Sumit Gupta
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Sameer Parekh
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Pramod Pujari
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Harish Rao
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Hitt Sharma
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Umesh Shaligram
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
| | - Sunil Gairola
- Clinical Bioanalytical Laboratory, Serum Institute of India Pvt. Ltd., Pune, Maharashtra, India
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Chen Z, Liu X, Zhang Y, Peng X, Zhang N, Chen N, Li Y, He Q. Evaluation of serum anti-pertussis toxin IgA antibodies for the diagnosis of Bordetella pertussis infection in young children. J Infect Public Health 2023; 16:1167-1173. [PMID: 37269695 DOI: 10.1016/j.jiph.2023.05.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 05/02/2023] [Accepted: 05/22/2023] [Indexed: 06/05/2023] Open
Abstract
BACKGROUND The determination of serum anti-pertussis toxin (PT) IgG antibodies is recommended for the diagnosis and surveillance of pertussis. However, the diagnostic power of anti-PT IgG can be hampered by possible interference from previous vaccinations. We aim to assess if anti-PT IgA antibodies can be well induced by Bordetella pertussis (B. pertussis) infections in children, and their capacity to improve pertussis serodiagnosis. METHODS Serum samples from 172 hospitalized children younger than 10 years old with confirmed pertussis were tested. Pertussis was confirmed by culture, PCR and/or serology. Anti-PT IgA antibodies were determined with commercial ELISA kits. RESULTS Sixty-four (37.2 %) subjects had anti-PT IgA antibodies greater than or equal to 15 IU/ml, and 52 (30.2 %) of them had anti-PT IgA antibodies greater than or equal to 20 IU/ml. No children with negative anti-PT IgG (less than 40 IU/ml) were observed to have anti-PT IgA antibodies greater than or equal to 15 IU/ml. Of patients younger than one year of age, about 50 % had an IgA antibody response. Moreover, the proportion of subjects with anti-PT IgA antibodies greater than or equal to 15 IU/ml among PCR negative subjects was significantly higher than that among PCR positive subjects (76.9 % vs 35.5 %). CONCLUSIONS The determination of anti-PT IgA antibodies does not seem to have added value for the serodiagnosis of pertussis in children older than one year of age. However, for infants, determination of serum anti-PT IgA antibodies appears to be useful for the diagnosis of pertussis especially when PCR and culture are negative. The results should be interpreted with caution as the number of subjects included in this study was limited.
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Affiliation(s)
- Zhiyun Chen
- Department of Medical Microbiology, Capital Medical University, Beijing, China
| | - Xiaoguai Liu
- The Third Department, Xi'an Children's Hospital, Xi'an, China
| | - Yuxiao Zhang
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, China
| | - Xiaokang Peng
- The Third Department, Xi'an Children's Hospital, Xi'an, China
| | - Nan Zhang
- Department of Medical Microbiology, Capital Medical University, Beijing, China
| | - Ning Chen
- Department of Medical Microbiology, Capital Medical University, Beijing, China; Center for adverse drug reactions monitoring of Beijing, Beijing, China
| | - Yarong Li
- The Third Department, Xi'an Children's Hospital, Xi'an, China.
| | - Qiushui He
- Department of Medical Microbiology, Capital Medical University, Beijing, China; Institute of Biomedicine, Research Center for Infections and Immunity, University of Turku, Turku, Finland.
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Fry NK, Campbell H, Amirthalingam G. JMM Profile: Bordetella pertussis and whooping cough (pertussis): still a significant cause of infant morbidity and mortality, but vaccine-preventable. J Med Microbiol 2021; 70. [PMID: 34668853 PMCID: PMC8604168 DOI: 10.1099/jmm.0.001442] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Whooping cough (pertussis) is a highly contagious respiratory bacterial infection caused by Bordetella pertussis and is an important cause of morbidity and mortality worldwide, particularly in infants. Bordetella parapertussis can cause a similar, but usually less severe pertussis-like disease. Bordetella pertussis has a number of virulence factors including adhesins and toxins which allow the organism to bind to ciliated epithelial cells in the upper respiratory tract and interfere with host clearance mechanisms. Typical symptoms of pertussis include paroxysmal cough with characteristic whoop and vomiting. Severe complications and deaths occur mostly in infants. Laboratory confirmation can be performed by isolation, detection of genomic DNA or specific antibodies. Childhood vaccination is safe, effective and remains the best control method available. Many countries have replaced whole-cell pertussis vaccines (wP) with acellular pertussis vaccines (aP). Waning protection following immunisation with aP is considered to be more rapid than that from wP. Deployed by resource-rich countries to date, maternal immunisation programmes have also demonstrated high efficacy in preventing hospitalisation and death in infants by passive immunisation through transplacental transfer of maternal antibodies.
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Affiliation(s)
- Norman K Fry
- Immunisation and Countermeasures Division, Public Health England - National Infection Service, London, UK.,Vaccine Preventable Bacteria Section, Public Health England - National Infection Service, London, UK
| | - Helen Campbell
- Immunisation and Countermeasures Division, Public Health England - National Infection Service, London, UK
| | - Gayatri Amirthalingam
- Immunisation and Countermeasures Division, Public Health England - National Infection Service, London, UK
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A New Electrochemiluminescence-Based Multiplex Assay for the Assessment of Human Antibody Responses to Bordetella pertussis Vaccines. Infect Dis Ther 2021; 10:2539-2561. [PMID: 34476771 PMCID: PMC8412870 DOI: 10.1007/s40121-021-00530-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Accepted: 08/13/2021] [Indexed: 01/19/2023] Open
Abstract
Introduction Commercially available enzyme-linked immunosorbent assay (ELISA) kits designed for pertussis diagnostic purposes are frequently used to assess antibody responses to pertussis vaccines in clinical trials, but have limited accuracy and are not calibrated against international standards. We developed a new electrochemiluminescence (ECL)-based multiplexed assay and compared its performance to two commercial Bordetella pertussis ELISA kits and to historical in-house ELISAs. Methods The ECL assay quantifies serum concentrations of antibodies against four B. pertussis antigens: pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (PRN), and fimbrial agglutinogen (FIM). The assay was validated for precision, accuracy, dilutability, lower limit of quantification, and specificity. Sera from a clinical trial (CTRI/2016/11/007434) were used to compare the ECL assay to two commercial ELISA kits available from GenWay BioTech and Demeditec Diagnostics for accuracy, linearity, specificity, and concordance to both internal (WWO-2-043) and international (NIBSC 06/140) references. Sera from four clinical trials (NCT02587520, NCT00255047, NCT00347958, NCT01346293) were used to compare the concordance to clinical ELISAs. Informed consent was ensured prior to using any sera. Results Precision, accuracy, dilutability, lower limit of quantification, and specificity were demonstrated for the ECL assay. Concordance between the ECL assay and established clinical ELISAs was met for antibody responses to PT, FIM, and PRN, but not for FHA. The ECL assay demonstrated higher accuracy and linearity than the ELISA kits. While concordance between the ECL and commercial kits was low, the ECL assay better distinguished between pre- and post-vaccination clinical samples. Conclusion The new ECL assay was validated for the quantitative evaluation of anti-PT, anti-FHA, anti-FIM, and anti-PRN IgG antibodies in samples from clinical trials, and demonstrated equivalent or better performance than two commercially available ELISA kits.
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Assessing the Quality of Serological Testing in the COVID-19 Pandemic: Results of a European External Quality Assessment (EQA) Scheme for Anti-SARS-CoV-2 Antibody Detection. J Clin Microbiol 2021; 59:e0055921. [PMID: 34190575 PMCID: PMC8373014 DOI: 10.1128/jcm.00559-21] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
External quality assessment (EQA) is a key instrument for achieving harmonization, and thus a high quality, of diagnostic procedures. As reliable test results are crucial for accurate assessment of SARS-CoV-2 infection prevalence, vaccine response, and immunity, and thus for successful management of the ongoing COVID-19 pandemic, the Reference Institute for Bioanalytics (RfB) was the first EQA provider to offer an open scheme for anti-SARS-CoV-2 antibody detection. The main objectives of this EQA were (i) to gain insights into the current diagnostic landscape and the performance of serological tests in Europe and (ii) to provide recommendations for diagnostic improvements. Within the EQA, a blinded panel of precharacterized human serum samples with variable anti-SARS-CoV-2 antibody titers was provided for detection of anti-SARS-CoV-2 IgG, IgA, and IgM antibodies. Across the three distribution rounds in 2020, 284 laboratories from 22 countries reported a total of 3,744 results for anti-SARS-CoV-2 antibody detection using more than 24 different assays for IgG. Overall, 97/3,004 results were false for anti-SARS-CoV-2 IgG, 88/248 for IgA, and 34/124 for IgM. Regarding diagnostic sensitivity and specificity, substantial differences were found between the different assays used, as well as between certified and noncertified tests. For cutoff samples, a drop in the diagnostic sensitivity to 46.3% and high interlaboratory variability were observed. In general, this EQA highlights the current variability of anti-SARS-CoV-2 antibody detection, technical limitations with respect to cutoff samples, and the lack of harmonization of testing procedures. Recommendations are provided to help laboratories and manufacturers further improve the quality of anti-SARS-CoV-2 serological diagnostics.
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Haselmann V, Özçürümez MK, Klawonn F, Ast V, Gerhards C, Eichner R, Costina V, Dobler G, Geilenkeuser WJ, Wölfel R, Neumaier M. Results of the first pilot external quality assessment (EQA) scheme for anti-SARS-CoV2-antibody testing. Clin Chem Lab Med 2020; 58:2121-2130. [PMID: 32853163 DOI: 10.1515/cclm-2020-1183] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 08/07/2020] [Indexed: 12/18/2022]
Abstract
Objectives Assessment of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection prevalence and immunity is cornerstones in the fight against COVID-19 pandemic. For pandemic control, reliable assays for the detection of anti-SARS-CoV-2 antibodies are required. This pilot external quality assessment (EQA) scheme aimed to independently assess the participants' clinical performance of anti-SARS-CoV-2 testing, to identify shortcomings in clinical practice and to evaluate the suitability of the scheme format. Methods The EQA scheme consisted of eight serum samples with variable reactivity against SARS-CoV-2 intended for the analysis of anti-SARS-CoV-2 immunoglobulin (Ig)G, IgA, and IgM antibodies. Laboratories reported: (1) results for each sample and the respective method, (2) raw data from replicate testing of each sample. Results The 16 selected pilot EQA participants reported 294 interpreted results and 796 raw data results from replicate testing. The overall error rate for the anti-SARS-CoV-2 IgG, IgA, and IgM tests was 2.7, 6.9, and 16.7%, respectively. While the overall diagnostic specificity was rated as very high, sensitivity rates between 67 and 98% indicate considerable quality differences between the manufacturers, especially for IgA and IgM. Conclusions Even the results reported by the small number of participants indicate a very heterogeneous landscape of anti-SARS-CoV-2 serological testing. Differences of available tests and the individual performance of laboratories result in a success rate of 57.1% with one laboratory succeeding for all three antibody-classes. These results are an incentive for laboratories to participate in upcoming open EQA schemes that are needed to achieve a harmonization of test results and to improve serological testing.
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Affiliation(s)
- Verena Haselmann
- Department of Clinical Chemistry, University Medicine Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany
| | - Mustafa K Özçürümez
- Department of Laboratory Medicine of the Medical Clinic at the University Medical Center Knappschaftskrankenhaus Bochum, Ruhr University, Bochum, Germany
| | - Frank Klawonn
- Biostatistics, Helmholtz Centre for Infection Research, Braunschweig, Germany.,Department of Computer Science, Ostfalia University of Applied Sciences, Wolfenbuttel, Germany
| | - Volker Ast
- Department of Clinical Chemistry, University Medicine Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany
| | - Catharina Gerhards
- Department of Clinical Chemistry, University Medicine Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany
| | - Romy Eichner
- Department of Clinical Chemistry, University Medicine Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany
| | - Victor Costina
- Department of Clinical Chemistry, University Medicine Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany
| | - Gerhard Dobler
- Bundeswehr Institute of Microbiology, Munich, Germany.,German Center for Infection Research (DZIF), Partner Site Munich, Munich, Germany
| | - Wolf-Jochen Geilenkeuser
- Reference-Institute for Bioanalytics, German Society for Clinical Chemistry and Laboratory Medicine (DGKL), Bonn, Germany
| | - Roman Wölfel
- Bundeswehr Institute of Microbiology, Munich, Germany.,German Center for Infection Research (DZIF), Partner Site Munich, Munich, Germany
| | - Michael Neumaier
- Department of Clinical Chemistry, University Medicine Mannheim, Medical Faculty Mannheim of the University of Heidelberg, Mannheim, Germany
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Gestal MC, Johnson HM, Harvill ET. Immunomodulation as a Novel Strategy for Prevention and Treatment of Bordetella spp. Infections. Front Immunol 2019; 10:2869. [PMID: 31921136 PMCID: PMC6923730 DOI: 10.3389/fimmu.2019.02869] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 11/22/2019] [Indexed: 12/13/2022] Open
Abstract
Well-adapted pathogens have evolved to survive the many challenges of a robust immune response. Defending against all host antimicrobials simultaneously would be exceedingly difficult, if not impossible, so many co-evolved organisms utilize immunomodulatory tools to subvert, distract, and/or evade the host immune response. Bordetella spp. present many examples of the diversity of immunomodulators and an exceptional experimental system in which to study them. Recent advances in this experimental system suggest strategies for interventions that tweak immunity to disrupt bacterial immunomodulation, engaging more effective host immunity to better prevent and treat infections. Here we review advances in the understanding of respiratory pathogens, with special focus on Bordetella spp., and prospects for the use of immune-stimulatory interventions in the prevention and treatment of infection.
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Affiliation(s)
- Monica C Gestal
- Department of Infectious Diseases, College of Veterinary Sciences, University of Georgia, Athens, GA, United States
| | - Hannah M Johnson
- Department of Infectious Diseases, College of Veterinary Sciences, University of Georgia, Athens, GA, United States
| | - Eric T Harvill
- Department of Infectious Diseases, College of Veterinary Sciences, University of Georgia, Athens, GA, United States
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Subissi L, Rodeghiero C, Martini H, Litzroth A, Huygen K, Leroux-Roels G, Piérard D, Desombere I. Assessment of IgA anti-PT and IgG anti-ACT reflex testing to improve Bordetella pertussis serodiagnosis in recently vaccinated subjects. Clin Microbiol Infect 2019; 26:645.e1-645.e8. [PMID: 31610300 DOI: 10.1016/j.cmi.2019.10.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2019] [Revised: 09/22/2019] [Accepted: 10/01/2019] [Indexed: 01/23/2023]
Abstract
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.
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Affiliation(s)
- L Subissi
- National Reference Centre (NRC) for Bordetella pertussis, Sciensano, Brussels, Belgium; European Programme for Public Health Microbiology Training, European Centre for Disease Prevention and Control, Stockholm, Sweden
| | - C Rodeghiero
- National Reference Centre (NRC) for Bordetella pertussis, Sciensano, Brussels, Belgium
| | - H Martini
- National Reference Centre (NRC) for Bordetella pertussis, Universitair Ziekenhuis, Brussel, Belgium
| | - A Litzroth
- Epidemiology of Infectious Diseases, Sciensano, Brussels, Belgium
| | - K Huygen
- National Reference Centre (NRC) for Bordetella pertussis, Sciensano, Brussels, Belgium
| | | | - D Piérard
- National Reference Centre (NRC) for Bordetella pertussis, Universitair Ziekenhuis, Brussel, Belgium
| | - I Desombere
- National Reference Centre (NRC) for Bordetella pertussis, Sciensano, Brussels, Belgium.
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