Pertussis seroprevalence among adults of reproductive age (20-39 years) in fourteen European countries.

The reported incidence of pertussis in European countries varies considerably. We aimed to study specific Bordetella pertussis seroprevalence in Europe by measuring serum IgG antibody levels to pertussis toxin (anti-PT IgG). Fourteen national laboratories participated in this study including Belgium, Denmark, Finland, Greece, Hungary, Italy, Lithuania, Malta, Norway, Poland, Portugal, Romania, Spain, and Sweden. Each country collected approximately 250 samples (N = 7903) from the age groups 20-29 years (N = 3976) and 30-39 years (N = 3927) during 2010-2013. Samples were anonymous residual sera from diagnostic laboratories and were analyzed at the national laboratories by a Swedish reference method, a commercial ELISA kit, or were sent to Sweden for analysis. The median anti-PT IgG concentrations ranged from 4 to 13.6 IU/mL. The proportion of samples with anti-PT IgG ≥100 IU/mL, indicating a recent infection ranged from 0.2% (Hungary) to 5.7% (Portugal). The highest proportion of sera with anti-PT IgG levels between 50 and <100 IU/mL, indicating an infection within the last few years, was found in Portugal (12.3%) and Italy (13.9%). This study shows that the circulation of B. pertussis is quite extensive in adults, aged 20-39 years, despite well-established vaccination programs in Europe.

Multilaboratory Comparison of Pneumococcal Multiplex Immunoassays Used in Immunosurveillance of Streptococcus pneumoniae across Europe.

Surveillance studies are required to estimate the impact of pneumococcal vaccination in both children and the elderly across Europe. The World Health Organization (WHO) recommends use of enzyme immunoassays (EIAs) as standard methods for immune surveillance of pneumococcal antibodies. However, as levels of antibodies to multiple serotypes are monitored in thousands of samples, a need for a less laborious and more flexible method has evolved. Fluorescent-bead-based multiplex immunoassays (MIAs) are suitable for this purpose. An increasing number of public health and diagnostic laboratories use MIAs, although the method is not standardized and no international quality assessment scheme exists. The EU Pneumo Multiplex Assay Consortium was initiated in 2013 to advance harmonization of MIAs and to create an international quality assessment scheme. In a multilaboratory comparison organized by the consortium, agreement among nine laboratories that used their own optimized MIA was assessed on a panel of 15 reference sera for 13 pneumococcal serotypes with the new WHO standard 007sp. Agreement was assessed in terms of assay accuracy, reproducibility, repeatability, precision, and bias. The results indicate that the evaluated MIAs are robust and reproducible for measurement of vaccine-induced antibody responses. However, some serotype-specific variability in the results was observed in comparisons of polysaccharides from different sources and of different conjugation methods, especially for serotype 4. On the basis of the results, the consortium has contributed to the harmonization of MIA protocols to improve reliability of immune surveillance of Streptococcus pneumoniaeIMPORTANCE Serology of Streptococcus pneumoniae is challenging due to existence of multiple clinically relevant serotypes and the introduction of multivalent vaccines in national immunization programs. Multiplex immunoassays (MIAs) are applied as high-throughput cost-effective methods for serosurveillance, and yet laboratories use their own protocols. The aims of this study were to assess the agreement of results generated by MIAs in different laboratories within the EU Pneumo Multiplex Assay Consortium, to analyze factors contributing to differences in outcome, and to create a harmonized protocol. The study demonstrated good agreement of results of MIAs performed by laboratories using controlled assays for determination of levels of vaccine-induced pneumococcal antibodies. The EU Pneumo Multiplex Assay Consortium is open to everyone working in public health services, and it aims to facilitate efforts by participants to run and maintain a cost-effective, reproducible, high-quality MIA platform.

Anti-pertussis antibody kinetics following DTaP-IPV booster vaccination in Norwegian children 7-8 years of age.

At the age of 7-8 years a booster of diphtheria, tetanus, acellular pertussis and polio vaccine is recommended for children in Norway. In this cross-sectional study we have analysed the antibody levels against pertussis vaccine antigens in sera from 498 children aged 6-12 years. The purposes of this study were to investigate the duration of the booster response against the pertussis vaccine antigens pertussis toxin (PT) and filamentous haemagglutinin (FHA); to determine the presence of high levels of pertussis antibodies in absence of recent vaccination; and to analyse how booster immunisation may interfere with the serological pertussis diagnostics. Prior to the booster the IgG antibody levels against PT revealed a geometric mean of 7.3IU/ml. After the booster the geometric mean peak anti-PT IgG response reached to 45.6IU/ml, followed by a steady decline in antibody levels over the next few years. The IgG anti-FHA levels followed the anti-PT IgG profiles. Three years after the booster the geometric mean IgG levels were only slightly above pre-booster levels. Prior to the booster 44% of the sera contained ≤5IU/ml of anti-PT IgG compared to18% 3 years after and 30% 4 years after the booster. When recently vaccinated children were excluded, 6.2% of the children had anti-PT IgG levels above 50IU/ml which may indicate pertussis infection within the last 2 years. This study indicates that the currently used acellular pertussis vaccines induce moderate immune responses to the pertussis antigens and that the antibodies wane within few years after the booster. This lack of sustained immune response may partly be responsible for the increased number of pertussis cases observed in this age group during the last years.

Immunization of teenagers with a fifth dose of reduced DTaP-IPV induces high levels of pertussis antibodies with a significant increase in opsonophagocytic activity.

Waning vaccine-induced immunity against Bordetella pertussis is observed among adolescents and adults. A high incidence of pertussis has been reported in this population, which serves as a reservoir for B. pertussis. A fifth dose of reduced antigen of diphtheria-tetanus-acellular-pertussis and inactivated polio vaccine was given as a booster dose to healthy teenagers. The antibody activity against B. pertussis antigens was measured prior to and 4 to 8 weeks after the booster by different assays: enzyme-linked immunosorbent assays (ELISAs) of IgG and IgA against pertussis toxin (PT) and filamentous hemagglutinin (FHA), IgG against pertactin (PRN), opsonophagocytic activity (OPA), and IgG binding to live B. pertussis. There was a significant increase in the IgG activity against PT, FHA, and PRN following the booster immunization (P < 0.001). The prebooster sera showed a geometric mean OPA titer of 65.1 and IgG binding to live bacteria at a geometric mean concentration of 164.9 arbitrary units (AU)/ml. Following the fifth dose, the OPA increased to a titer of 360.4, and the IgG concentration against live bacteria increased to 833.4 AU/ml (P < 0.001 for both). The correlation analyses between the different assays suggest that antibodies against FHA and PRN contribute the most to the OPA and IgG binding.

Critical roles of complement and antibodies in host defense mechanisms against Neisseria meningitidis as revealed by human complement genetic deficiencies.

Certain complement defects are associated with an increased propensity to contract Neisseria meningitidis infections. We performed detailed analyses of complement-mediated defense mechanisms against N. meningitidis 44/76 with whole blood and serum from two adult patients who were completely C2 or C5 deficient. The C5-deficient patient and the matched control were also deficient in mannose-binding lectin (MBL). The proliferation of meningococci incubated in freshly drawn whole blood was estimated by CFU and quantitative DNA real-time PCR. The serum bactericidal activity and opsonophagocytic activity by granulocytes were investigated, including heat-inactivated postvaccination sera, to examine the influence of antimeningococcal antibodies. The meningococci proliferated equally in C2- and C5-deficient blood, with a 2 log(10) increase of CFU and 4- to 5-log(10) increase in DNA copies. Proliferation was modestly decreased in reconstituted C2-deficient and control blood. After reconstitution of C5-deficient blood, all meningococci were killed, which is consistent with high antibody titers being present. The opsonophagocytic activity was strictly C2 dependent, appeared with normal serum, and increased with postvaccination serum. Serum bactericidal activity was strictly dependent on C2, C5, and high antibody titers. MBL did not influence any of the parameters observed. Complement-mediated defense against meningococci was thus dependent on the classical pathway. Some opsonophagocytic activity occurred despite low levels of antimeningococcal antibodies but was more efficient with immune sera. Serum bactericidal activity was dependent on C2, C5, and immune sera. MBL did not influence any of the parameters observed.

Opsonophagocytic activity and other serological indications of Bordetella pertussis infection in military recruits in Norway.

Bordetella pertussis is the causative agent of pertussis (whooping cough). Despite high vaccination coverage, pertussis remains a significant disease in many countries. Besides vaccination, transient carriage of Bordetella spp. or other cross-reacting organisms adds to the immunity against pertussis. However, the various immunological mechanisms conferring protection remain largely unknown. In this study, paired serum samples from 464 healthy Norwegian military recruits were collected, the first at enrolment and the second about 8 months later. The prevalence of pertussis during military service was examined by comparing the paired serum samples for immunoglobulin G (IgG) antibodies against pertussis toxin (PT) by enzyme-linked immunosorbent assay (ELISA). Seventy-eight percent of the recruits had low levels of IgG antibodies against PT in both samples. Conversely, 8.4% of the recruits demonstrated high anti-PT IgG levels in the first sample, indicative of recent pertussis prior to enrolment. One recruit experienced seroconversion, indicating pertussis during service. A subset of 248 serum samples with low, medium, and high anti-PT IgG titers were analyzed by a different ELISA kit for IgG and IgA antibodies against PT and filamentous hemagglutinin (FHA) and for opsonophagocytic activity (OPA), for induction of C3b deposition products, and for IgG binding with live B. pertussis as the antigen. We observed high correlations between OPA and IgG against live bacteria (r = 0.83), between OPA and IgG anti-FHA (r = 0.79), between OPA and anti-PT IgG (r = 0.68), and between OPA and C3b binding (r = 0.70) (P < 0.0001 for all). Anti-PT IgA did not correlate closely with the other assays.