Markers of hepatitis B virus infection and immunity in Victoria, Australia, 1995 to 2005.

OBJECTIVE: Estimating the prevalence of chronic hepatitis B virus (HBV) infection in generally low-prevalence populations containing communities with a higher disease burden is difficult. This study was conducted to estimate the prevalence of serological markers of infection with, and immunity to, HBV in the Victorian population and to analyse trends in these estimates over time. METHODS: A serological survey of 3,212 samples of convenience collected in the years 1995, 2000 and 2005 was conducted using a selection procedure designed to reduce selection bias. All samples were tested for hepatitis B surface and core antibodies; all core antibody positive samples (indicating previous infection) were then tested for the presence of hepatitis B surface antigen (HBsAg). RESULTS: HBsAg prevalence was 1.1% (95%CI 0.8-1.6%) with significant differences observed by area of residence, age, gender and test year. Serological evidence of immunisation in infants and adolescents were lower than established estimates following the introduction of universal vaccination for these groups. CONCLUSIONS: This study emphasises the significant and growing problem of chronic HBV infection in Victoria and suggests lower than expected population immunity deriving from universal vaccination programs. IMPLICATIONS: Greater efforts are needed to formulate a comprehensive public health response to address this relatively neglected blood borne viral infection, the burden of which is very significant in some marginalised sections of our community. Increased attention to improving the universality of our immunisation programs is also needed.

Improving HIV surveillance in Victoria: the role of the "detuned" enzyme immunoassay.

Between 1999 and 2000, new diagnoses of HIV in Victoria (Australia) rose by 41%, from 140 to 197. In this time period, sera from new HIV diagnoses were tested using the Organon Teknika "detuned" enzyme immunoassay (EIA). We compared the results of the detuned EIA with incident infections defined by surveillance (on the basis of a previous negative or indeterminate HIV test and/or a seroconversion illness within the 12 months preceding HIV diagnosis). Of 317 specimens, 97 (31%) incident infections and 114 (36%) recent infections were detected using surveillance and detuned EIA, respectively. The detuned assay misclassified 11 cases with AIDS and 2 cases with CD4 counts < or = 200 micro3 (probable long-standing infections) as recent infections and was unable to identify 31 (32%) of 97 cases previously classified as incident cases by surveillance. The assay detected an extra 35 recent infections that were previously classified as nonincident by surveillance. By combining the detuned assay and surveillance, 132 (42%) incident infections were identified from 317 specimens, 36% more than surveillance alone. We recommend that a detuned assay or similar test become part of the routine strategy to identify incident infections in Victoria. Incident infections provide important information for targeting prevention strategies and the opportunity to interrupt ongoing viral transmission.