Between 2003 and 2006, we carried out a cross-sectional, population-based, sero-epidemiological survey on hepatitis virus infections in the province of Naples. Methods of this survey have been previously described in detail . Briefly, 4496 randomly selected individuals (aged 20 years or more), after signing informed consent, donated a blood sample and completed a standardized questionnaire, which included questions on HBV infected households and on HBV vaccination. The study protocol conformed to the 1975 Declaration of Helsinki and had been approved by the CCR Board of Ethics.
Sera were tested for hepatitis B surface antigen (HBsAg) and for antibodies to HBV-core antigen (anti-HBc) using enzyme immunoassays (Cobas Core ll, Roche Diagnostics, Indianapolis, IN, USA); for antibodies to HBV-surface antigen (anti-HBs) by enzyme immunoassays (Anti-HBs Quant EIA II – Roche Diagnostics): samples with a reactivity >10 IU/L were considered positive .
For the purpose of this analysis, positive results for anti-HBc were considered to indicate past or current HBV infection, while positivity for anti-HBsAg (anti-HBs) only was considered indicative of HBV vaccination-induced immunity. Individuals who tested negative for all HBV serological markers were considered as non immune/non infected.
Prevalence of past or current HBV infection and of HBV vaccination-induced immunity was calculated in two vaccination target populations i.e. persons born ≥ 1980 and household contacts of an HBV carrier. To analyze the association of epidemiological and socioeconomic characteristics with HBV vaccination of household contacts, we compared, among those born before 1980, individuals with immune protection with those not immune/not infected. As a measure of association, we calculated odds ratio (OR) and multivariate logistic regression odds ratio (MLR-OR) and their 95% confidence intervals (95% CI). The MLR was adjusted for gender, age, as a priori chosen variables, and for variables significantly associated with immune protection in univariate analysis. We also performed a sensitivity analysis considering as "vaccinated", subjects that reported to have been vaccinated but testing negative for anti-HBs.
To evaluate agreement between vaccination status according to self-report and that obtained from laboratory results, we calculated the percentage of agreement and the kappa (k) statistic. Statistical analyses were performed using SPSS package (version 15.00 SPSS Inc., Chicago, Illinois).