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

A standardisation process, already developed during the earlier European Sero-Epidemiology Network (ESEN) project, was employed with a more robust algorithm to harmonise results of pertussis serological assays performed in 12 European and non-European countries. Initially, results from each country's own assay were compared with those obtained at the reference laboratory by means of an in-house pertussis toxin (PT)-based ELISA: seven countries used in-house or commercial PT-ELISAs; the other countries used assays based on Bordetella pertussis whole cell extracts (WCE) (three countries) or on combined PT-FHA (filamentous haemagglutinin) antigenic preparations (two countries). The WCE assays, although admitted for diagnostic purposes, confirmed their low correlation with the PT-ELISAs and their results could not be used for standardisation; the PT-FHA ELISAs gave results that were suitable for standardisation in one country but unsatisfactory in the other; the use of purified PT in serological assays confirmed its better reliability than other preparations and all PT-ELISAs results could be calibrated against those of the reference centre. In the standardisation process two high-titre cut-offs indicative of likelihood of recent infection (from within 4 weeks of disease onset up to 1 year after) were included for evaluations as they are suggested to be more useful, for the sero-epidemiological assays of immunity to pertussis, than the cut-off of protection, commonly employed, but still not defined for pertussis. Providing PT-ELISAs are used, standardisation of pertussis assay results is always possible and, when standardisation is performed, evaluation and comparison of the impact of different interventions can be also allowed, by measuring at the distribution of high antibody titres in the populations.

A population-based prevalence study of hepatitis A, B and C virus using oral fluid in Flanders, Belgium.

Ten years after the first seroprevalence study performed in Flanders, the aim of this cross sectional study was to follow the evolution of hepatitis A, B and C prevalence. The prevalence of hepatitis A antibodies, hepatitis B surface antigen and hepatitis C antibodies was measured in oral fluid samples collected by postal survey. Using the National Population Register, an incremental sampling plan was developed to obtain a representative sampling of the general population. A total of 24,000 persons were selected and 6,000 persons among them contacted in a first wave. With 1834 participants a response rate of 30.6% was achieved. The prevalence was weighted for age and was 20.2% (95% CI 19.43-21.08) for hepatitis A, 0.66% (95% CI 0.51-0.84) for hepatitis B surface antigen and 0.12% (95% CI 0.09-0.39) for hepatitis C. The prevalence of hepatitis A and C in the Flemish population is lower in 2003 compared with the results of the study performed in 1993. The difference may be due to a real decrease of the diseases but also to differences in the methodology. The prevalence of hepatitis B surface antigen remains stable. Considering the 30% response rate and the high quality of the self-collected samples as reflect of a good participation of the general population, saliva test for prevalence study is a good epidemiological monitoring tool.

European seroepidemiology network 2: Standardisation of assays for seroepidemiology of varicella zoster virus.

BACKGROUND: The aim of the European Sero-Epidemiology Network (ESEN2) is to harmonise the serological surveillance of vaccine-preventable diseases in Europe. OBJECTIVE: To allow comparison of antibody prevalence in different countries by standardising results into common units. STUDY DESIGN: For varicella zoster virus (VZV), a reference laboratory established a panel of 148 samples, characterised by indirect enzyme-immunoassay (ELISA), indirect immunofluorescence, and complement fixation test. Fifty-seven samples were also studied by the fluorescence antibody to membrane antigen test. The geometric mean of the antibody activity (GMAA) obtained from four ELISA determinations was used to characterise each sample of the panel as positive (GMAA: >100 mIU/ml), equivocal (GMAA: 50-100 mIU/ml) or negative (GMAA: <50 mIU/ml) for antibody to VZV (anti-VZV). Thirteen laboratories, using five different ELISA tests, tested the panel. RESULTS: Agreement with the reference laboratory was above 85% in all cases, and the R(2) values obtained from regression analysis of the quantitative results were always higher than 0.87. Finally, the regression equations could be used to convert national values into a common unitage. CONCLUSION: This study confirmed that results for anti-VZV obtained by different ELISA methods can be converted into common units, enabling the comparison of the seroprevalence profiles obtained in the participant countries.

Oral fluid as a medium for the detection of hepatitis B surface antigen.

Currently viral antigens and antibodies are detected by traditional serological tests. However, the introduction of oral fluid as an alternative medium would allow other alternatives. The collection of oral fluid is, in comparison with venepuncture, less invasive, less painful, less expensive (i.e., no trained personal required), and safe (prevention of needle stick injuries). Also large numbers of samples can be collected easily for epidemiological purposes. Forty-three HBsAg positive and seventy-three HBsAg negative paired serum/oral fluid samples were tested. They were collected from patients attending university hospitals. The oral fluid samples were collected using the Oracol collection device and they were subjected to an IgG quantification assay to ensure their quality and quantity. The detection of HBsAg in oral fluid was carried out using a modified ETI-MAK-4 ELISA. The validation of this oral fluid test gave a sensitivity and specificity of 90.7% and 100%, respectively. The modified ETI-MAK-4 ELISA is a suitable test for oral fluid samples collected by the Oracol collection device for epidemiological purposes.

The seroepidemiology of primary varicella-zoster virus infection in Flanders (Belgium).

UNLABELLED: The age-specific seroprevalence of varicella-zoster virus (VZV) antibodies was assessed in a sample of the Flemish (Belgian) population. ELISA tests were used to analyse 1673 sera from subjects aged 1 to 44 years (October 1999-April 2000). Chickenpox infections in Flanders appear to affect children at a younger age than in other European countries since 47.37% (95% CI: 37.33-57.41) is already immune at 2 years of age. For older age-groups, the prevalence is similar to that of most European countries: 80.19% (95% CI: 72.60-87.78) at 5 years, 92.52% (95% CI: 87.54-97.51) at 9 years and 100%> or =40 years. The accuracy of non-positive recollections of varicella histories among Flemish 10 to 17-year olds was examined on the basis of a second (residual) serum bank. In this group, VZV seroprevalence was almost always 100% (or nearly 100%), irrespective of age, degree of reliability (negative or uncertain answers) or level of ascertainment (child personally or parents). The limited size of this second data set did not allow for an accurate assessment of the negative predictive value of such recollections. CONCLUSION: since varicella-zoster virus predominantly affects very small children and is generally perceived as benign, the required high coverage rate of a universal childhood varicella vaccination programme may be hard to attain. Adolescent strategies can minimise the population risks involved but the accuracy of non positive antecedents of chickenpox needs to be documented to assess the efficiency of such strategies.