European Sero-Epidemiology Network 2: standardisation of immunoassay results for pertussis requires homogeneity in the antigenic preparations

Immunization with a Synthetic Helicobacter pylori Peptide Induces Secretory IgA Antibodies and Protects Mice against Infection

Helicobacter pylori is a spiral Gram-negative bacterium associated with inflammation of the gastric mucosa, peptic ulcer, and gastric adenocarcinoma, whose treatment has failed due to antibiotic resistance and side effects. Furthermore, because there are no vaccines effective against H. pylori, an appropriate vaccine design targeting conserved/essential genes must be identified. In the present study, a H. pylori 50-52 kDa immunogen-derived peptide antigen with the sequence Met-Val-Thr-Leu-Ile-Asn-Asn-Glu (MVTLINNE) was used to immunize against H. pylori infection. For this, mice received an intraperitoneal injection of 100 μg of H. pylori peptide on the first week, followed by two weekly subcutaneous reinforcements and further 109 bacteria administration in the drinking water for 3 weeks. Thymic cells proliferative responses to concanavalin A, serum levels of IL-2, IL-4, IL-6, IL-10, IL-17, IFN-γ, and TNF-α cytokines, and IgG1, IgG2a, IgG2b, IgG3 IgM, and IgA immunoglobulins were evaluated. Significant (p < 0.05) increases on lymphoproliferation and spleen weights after immunization were observed. In contrast, infection significantly (p < 0.05) decreased lymphoproliferation, which was recovered in immunized mice. In addition, levels of serum TH1 and TH2 cytokines were not altered after immunization, except for the significant increase in IL-6 production in immunized and/or infected animals. Moreover, immunization correlated with plasma secretory IgA and IgG, whereas infection alone only elicited IgM antibodies. Peptide immunization protected 100% of mice against virulent H. pylori. MVTLINNE peptide deserves further research as an approach to the prophylaxis of H. pylori infection.

The Use of Innovative Two-Component Cluster Analysis and Serodiagnostic Cut-Off Methods to Estimate Prevalence of Pertussis Reinfections

Bordetella pertussis circulates even in highly vaccinated countries affecting all age groups. Insight into the scale of concealed reinfections is important as they may contribute to transmission. We therefore investigated whether current single-point serodiagnostic methods are suitable to estimate the prevalence of pertussis reinfection. Two methods based on IgG-Ptx plasma levels alone were used to evaluate the proportion of renewed seroconversions in the past year in a cohort of retrospective pertussis cases ≥ 24 months after a proven earlier symptomatic infection. A Dutch population database was used as a baseline. Applying a classical 62.5 IU/ml IgG-Ptx cut-off, we calculated a seroprevalence of 15% in retrospective cases, higher than the 10% observed in the population baseline. However, this method could not discriminate between renewed seroconversion and waning of previously infection-enhanced IgG-Ptx levels. Two-component cluster analysis of the IgG-Ptx datasets of both pertussis cases and the general population revealed a continuum of intermediate IgG-Ptx levels, preventing the establishment of a positive population and the comparison of prevalence by this alternative method. Next, we investigated the complementary serodiagnostic value of IgA-Ptx levels. When modelling datasets including both convalescent and retrospective cases we obtained new cut-offs for both IgG-Ptx and IgA-Ptx that were optimized to evaluate renewed seroconversions in the ex-cases target population. Combining these cut-offs two-dimensionally, we calculated 8.0% reinfections in retrospective cases, being below the baseline seroprevalence. Our study for the first time revealed the shortcomings of using only IgG-Ptx data in conventional serodiagnostic methods to determine pertussis reinfections. Improved results can be obtained with two-dimensional serodiagnostic profiling. The proportion of reinfections thus established suggests a relatively increased period of protection to renewed infection after clinical pertussis.

Estimating seroprevalence of vaccine-preventable infections: is it worth standardizing the serological outcomes to adjust for different assays and laboratories?

The aim of the European Sero-Epidemiology Network 2 (ESEN2) project was to estimate age-specific seroprevalence for a number of vaccine-preventable diseases in Europe. To achieve this serosurveys were collected by 22 national laboratories. To adjust for a variety of laboratory methods and assays, all quantitative results were transformed to a reference laboratory's units and were then classified as positive or negative to obtain age-specific seroprevalence. The aim of this study was to assess the value of standardization by comparing the crude and standardized seroprevalence estimates. Seroprevalence was estimated for measles, mumps, rubella, diphtheria, varicella zoster and hepatitis A virus (HAV) and compared before and after serological results had been standardized. The results showed that if no such adjustment had taken place, seroprevalence would have differed by an average of 3·2% (95% bootstrap interval 2·9-3·6) although this percentage varied substantially by antigen. These differences were as high as 16% for some serosurveys (HAV) which means that standardization could have a considerable impact on seroprevalence estimates and should be considered when comparing serosurveys performed in different laboratories using different assay methods.

Issues and considerations in the use of serologic biomarkers for classifying vaccination history in household surveys

Accurate estimates of vaccination coverage are crucial for assessing routine immunization program performance. Community based household surveys are frequently used to assess coverage within a country. In household surveys to assess routine immunization coverage, a child's vaccination history is classified on the basis of observation of the immunization card, parental recall of receipt of vaccination, or both; each of these methods has been shown to commonly be inaccurate. The use of serologic data as a biomarker of vaccination history is a potential additional approach to improve accuracy in classifying vaccination history. However, potential challenges, including the accuracy of serologic methods in classifying vaccination history, varying vaccine types and dosing schedules, and logistical and financial implications must be considered. We provide historic and scientific context for the potential use of serologic data to assess vaccination history and discuss in detail key areas of importance for consideration in the context of using serologic data for classifying vaccination history in household surveys. Further studies are needed to directly evaluate the performance of serologic data compared with use of immunization cards or parental recall for classification of vaccination history in household surveys, as well assess the impact of age at the time of sample collection on serologic titers, the predictive value of serology to identify a fully vaccinated child for multi-dose vaccines, and the cost impact and logistical issues on outcomes associated with different types of biological samples for serologic testing.

Prospective evaluation of an Australian pertussis toxin IgG and IgA enzyme immunoassay

Serological diagnosis of recent pertussis infection is an important part of both clinical assessment and epidemiological documentation of this disease. Standardization of serological testing and interpretation remains challenging despite international efforts to improve it. Currently, determining the anti-pertussis toxin (PT) IgG titer is recommended as the most accurate serological test in Europe and the United States, while Australia relies predominantly on measurement of Bordetella pertussis IgA antibody responses. Using B. pertussis PCR and the WHO clinical case definition as reference standards, the diagnostic utility of in-house anti-PT IgG and anti-PT IgA assays was evaluated prospectively in an Australian community-based cohort (n = 327). Patients provided up to four consecutive serum samples to document the kinetics of antibody response and decay. Previously validated cutoffs for positivity were converted to international units by using WHO-approved reference sera. At currently used cutoffs, both anti-PT IgG (>94 IU/ml) and anti-PT IgA (>20 IU/ml) assays had good specificity (80% [95% confidence interval {95% CI}, 68 to 88%] and 87% [95% CI, 77 to 94%]), but anti-PT IgG assay was consistently more sensitive than anti-PT IgA assay across a range of cutoffs (60 to 79% [95% CI, 53 to 84%] versus 41 to 62% [95% CI, 34 to 69%]). The combination of anti-PT IgG and anti-PT IgA assays performed no better than anti-PT IgG assay alone. The anti-PT IgA response in children under 12 years of age was poor. The accuracy of serology was optimal between 2 and 8 weeks after symptom onset. Cutoffs of >94 IU/ml for anti-PT IgG and >20 IU/ml for anti-PT IgA correlated well with recent pertussis infection and were consistent with recent recommendations from the EU Pertstrain group. Anti-PT IgG assay was superior to anti-PT IgA assay as the test of choice for the diagnosis of pertussis from a single sample.

Comparative study of different sources of pertussis toxin (PT) as coating antigens in IgG anti-PT enzyme-linked immunosorbent assays

In an effort to improve the reliability and reproducibility of serological assays for Bordetella pertussis, a collaborative study was conducted to compare four different sources of pertussis toxin (PT) as coating antigens in the immunoglobulin G (IgG) anti-PT enzyme-linked immunosorbent assay (ELISA). Four sources of PT were used as coating antigens in the IgG anti-PT ELISA in four different testing laboratories (labs A to D) to determine whether the different antigen preparations and different laboratories influenced assay results. A panel of 60 sera consisting of deidentified human specimens from previous vaccination trials of healthy adults and infants and clinical specimens from outbreak settings was tested. In the four laboratories, each sample was tested three times with the four PT antigens according to the standard coating optimization and IgG anti-PT ELISA testing procedures used in that laboratory. Differences among the antigens, as well as intra- and interlaboratory variability, were evaluated. Excellent agreement was observed with the test panel results among the four antigens within each laboratory. Concordance correlation coefficient (r(c)) measurements among the different antigens ranged from 0.99, 0.99 to 1.00, 1.00, and 0.97 to 1.00 for labs A to D, respectively. The comparisons between pairs of laboratories also indicated a high degree of concordance for each PT preparation, with r(c) measurements between 0.90 and 0.98, 0.93 and 0.99, 0.92 and 0.98, and 0.93 and 0.99 for antigens 1 to 4, respectively. Relatively minor differences in results were observed among laboratories or among antigens, suggesting that the four PT antigens are quite similar and could be considered for acceptance in harmonized immunoassays used for serodiagnosis or vaccine evaluation.

EUVAC.NET collaborative study: evaluation and standardisation of serology for diagnosis of pertussis

As part of the new EUVAC.NET contract with ECDC (Pertussis Work Area 4), a collaborative study was organised in July-December 2010. Two well-defined reference preparations with high and low IgG antibodies to pertussis toxin (PT), were sent to participants. The purposes of this study were to assess current laboratory performance of serological assays for pertussis; to compare in-house reference preparations that are currently used by participants for the serological assay; and to identify needs for standardisation of the serological assay. Reference Laboratories in Europe currently performing serological assays for the diagnosis of pertussis by measuring antibody to PT, were invited to participate in the study. A total of 17 laboratories/countries participated in this study. Results were reported from a total of 9 participants who used in-house ELISA assays and 10 participants who used commercial kits. All participants using in-house ELISA with purified PT coating plates distinguished the 2 preparations and gave results that were comparable to the expected values. A total of 6 commercial kits included in the study showed different results. The kits coated with mixture antigens did not appear to be able to give results that were correlated to the WHO reference preparations.

Comparison of Western immunobloting to an enzyme-linked immunosorbent assay for the determination of anti-Bordetella pertussis antibodies

During Bordetella pertussis infection, it has been established that an increase of anti-pertussis toxin (PT) and anti-filamentous hemagglutinin (FHA) antibodies occurs. Immunoblots from two manufacturers using FHA and PT antigens were compared with an enzyme-linked immunosorbent assay (ELISA) that used both FHA and PT. One manufacturer used two concentrations of PT bands for the IgG immunoblot, calibrated to the World Health Organization standard for PT in international units (IU/ml), 100 IU/ml (PT-100) and 8 IU/ml (PT). The second immunoblot kit measured antibodies to a single calibrated PT band. Both kits measured IgA antibodies, and one additionally measured IgM antibodies. Two of 41 (5%) ELISA IgM positives were confirmed positive by IgM immunoblotting, suggesting poor specificity of the IgM ELISA. The agreements of the IgG and IgA immunoblots with the ELISA ranged from 72.5% to 85.3%, with only 38 to 51% of IgA positives confirmed by immunoblotting and only 61 to 68% of IgG positives confirmed by immunoblotting. The two immunoblots correlated well with each other, with 91.7% and 94.3% agreement for IgG and IgA, respectively. When the FHA band was used with the PT band as the criterion for positivity, significant differences existed in specificity compared to the ELISA (IgG, 84.1% versus 33.3%; IgA, 82.4% versus 71.0%). When the positive IgA immunoblots (evidence of natural recent infection) were compared to the positive PT-100 IgG immunoblots (evidence of recent infection or vaccination), the PT-100 blot showed a 71% sensitivity in detecting natural recent infection. B. pertussis immunoblots, alone or in combination with ELISAs, can aid in the diagnosis of B. pertussis infection.

Performance of commercial enzyme-linked immunosorbent assays for detection of antibodies to Bordetella pertussis

Measuring antibodies to Bordetella pertussis antigens is mostly done by enzyme-linked immunosorbent assays (ELISAs). We compared the performance of ELISA kits that were commercially available in Germany. Eleven measured IgG antibodies, and nine measured IgA antibodies. An in-house ELISA with purified antigens served as a reference method. Samples included two WHO reference preparations, the former Food and Drug Administration (FDA)/Center for Biologics Evaluation and Research (CBER) reference preparations, serum samples from patients with clinically suspected pertussis, and serum samples from patients having received a combined tetanus, diphtheria, and pertussis (Tdap) vaccination. Kits using pertussis toxin (PT) as an antigen showed linearity compared to the WHO Reference preparation (r2 between 0.82 and 0.99), and these kits could quantify antibodies according to the reference preparation. ELISA kits using mixed antigens showed no linear correlation to the reference preparations. Patient results were compared to results of in-house ELISAs using a dual cutoff of either ≥100 IU/ml anti-PT IgG or ≥40 IU/ml anti-PT IgG together with ≥12 IU/ml anti-PT IgA. The sensitivities of kits measuring IgG antibodies ranged between 0.84 and 1.00. The specificities of kits using PT as an antigen were between 0.81 and 0.93. The specificities of kits using mixed antigens were between 0.51 and 0.59 and were thus not acceptable. The sensitivities of kits measuring IgA antibodies ranged between 0.53 and 0.73, and the specificities were between 0.67 and 0.94, indicating that IgA antibodies may be of limited diagnostic value. Our data suggest that ELISAs should use purified PT as an antigen and be standardized to the 1st International Reference preparation.

The impact of additional pertussis vaccine doses on disease incidence in children and infants

BACKGROUND

Pertussis remains a cause of considerable morbidity in children worldwide. Due to the resurgence of the disease, two vaccine doses for schoolchildren were added to the routine Israeli schedule. In 2005 a 5th dose was introduced for second-graders (aged 7-8), and in 2008 an additional catch-up dose in the eighth grade (13-14 year-olds).

METHODS

Population-based epidemiologic study of pertussis in the Jerusalem district.

RESULTS

1736 pertussis cases were reported from 1990 to 2009. The pertussis incidence rates increased sharply from 2.6/100,000 in 1990, to 10/100,000 in 2000, peaking at 28.8/100,000 in 2006, then declining to 22/100,000 in 2008 and to 15.7 in 2009 (2006 vs. 2009, p=0.0001). Most cases (74.4%, 1134/1524 during 1998-2009) were under 20 years. Infants under one year had the highest average incidence rate (72.3/100,000; 12.5% of cases); specifically those under 6 months (84.3% of cases under one year). The case distribution among 1-4, 5-9, 10-14, and 15-19 year-olds was: 11%, 18%, 24.1%, and 8.9%. The vaccination status (age-appropriate) was: unvaccinated--19.2%, partially vaccinated--7.6%, and fully vaccinated--73.2%. The overall hospitalization rate was 5.4%; infants--33.5%. Household transmission occurred in 16.1% of cases. The two age groups showing significant decline were children aged 5-9 (61.5% reduction) and 10-14 years (73.9% reduction); there is as yet no significant decline in other age groups.

CONCLUSIONS

The recent marked decline in pertussis incidence among the 5-14 year-olds is encouraging. Young infants still constitute a significant disease burden, and the incidence in this age group should be followed closely.

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

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

Development and analytical validation of an immunoassay for quantifying serum anti-pertussis toxin antibodies resulting from Bordetella pertussis infection

Adequately sensitive and specific methods to diagnose pertussis in adolescents and adults are not widely available. Currently, no Food and Drug Administration-approved diagnostic assays are available for the serodiagnosis of Bordetella pertussis. Since concentrations of B. pertussis-specific antibodies tend to be high during the later phases of disease, a simple, rapid, easily transferable serodiagnostic test was developed. This article describes test development, initial evaluation of a prototype kit enzyme-linked immunosorbent assay (ELISA) in an interlaboratory collaborative study, and analytical validation. The data presented here demonstrate that the kit met all prespecified criteria for precision, linearity, and accuracy for samples with anti-pertussis toxin (PT) immunoglobulin G (IgG) antibody concentrations in the range of 50 to 150 ELISA units (EU)/ml, the range believed to be most relevant for serodiagnosis. The assay met the precision and linearity criteria for a wider range, namely, from 50 to 200 EU/ml; however, the accuracy criterion was not met at 200 EU/ml. When the newly adopted World Health Organization International Standard for pertussis antiserum (human) reference reagent was used to evaluate accuracy, the accuracy criteria were met from 50 to 200 international units/ml. In conclusion, the IgG anti-PT ELISA met all assay validation parameters within the range considered most relevant for serodiagnosis. This ELISA was developed and analytically validated as a user-friendly kit that can be used in both qualitative and quantitative formats. The technology for producing the kit is transferable to public health laboratories.