Molecular epidemiology of hepatitis B virus infections in Denmark
Introduction
The prevalence of hepatitis B virus infection (HBV) in Denmark is low. In two recent surveys we found that 0.7% of blood donors (Christensen et al., 2001a) and 1.6% among hospital employees (Fisker et al., 2004a) were anti-HBc positive. The reported Danish HBV incidence of acute hepatitis B infection is 1/100,000 per year and has been declining for the last decades. In the same period, however, the number of immigrants from HBV endemic regions has more than doubled. It is unknown to what extent acute HBV infections relate to this population. Due to the low levels of infection Denmark has not followed the WHO recommendation of universal childhood immunisation against HBV (Iwarson, 1998) but screening and/or vaccination of individuals belonging to high risk groups, e.g. injecting drug users (IDUs), immigrants and blood exposed health care workers, is recommended. Notification of acute symptomatic HBV infection has been mandatory for more than 20 years but reporting was recently shown to be incomplete with a notification rate of 38% to the surveillance system (Christensen et al., 2001b). Chronic hepatitis B infection has been notifiable since May 2000. Roughly, one-third of acute cases has been attributed to sexual transmission and one-third to injecting drug use, while the route of transmission in the remaining cases has been unknown.
It is not known to what extent the probable increasing number of chronic carriers influences transmission in the general population. The aims of this study were to characterise all consecutive cases of both chronic and acute HBV infection in a geographical region within a 2 year period and to examine to what extend chronically HBV infected individuals from different risk groups contributed to acute HBV infections. The analysis aimed on whether HBV was transmitted between different risk groups rather than on details of transmission between individuals within these groups.
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Study population
Hepatitis B serology in the County of Funen is performed almost exclusively at the Department of Clinical Immunology, Odense University Hospital. Upon requisition it is indicated whether HBV serology is performed due to suspicion of acute hepatitis, chronic hepatitis (screening of risk groups and symptomatic patients), before or after vaccination (including as post exposure protection) or during follow-up of already known infection. During year 2000 approximately 2200, 2800, 650, and 150
Participants
The case definition was met in 315 individuals of whom six HBsAg negative individuals were excluded due to persistent anti-HBc IgM. Hereafter 309 eligible cases were surveyed. The index sample was HBeAg positive in 30% (93), HBeAg negative/HBsAg positive in 63.5% (196) and HBsAg negative but anti-HBc IgM positive (<6 months) in 6.5% (20). Clinical data was available in 90% (278) of cases. In the 72 cases interviewed (18 with acute infection), the information obtained was in accordance with the
Discussion
Based on cases routinely identified in a regional clinical laboratory, the annual incidence of acute hepatitis B infection was 9.6 per 100,000 per year, three times higher than the county specific reported incidence of 3.0 per 100,000 per year (Lemcke, 2002). The low reporting rate of 31% are in agreement with our previous findings of 38% of acute hepatitis reported to the surveillance system (Christensen et al., 2001b) and indicates that laboratory reporting could improve the Danish hepatitis
Conclusions
The current hepatitis B surveillance system underestimates the occurrence of both acute and chronic hepatitis B in Denmark and we suggest implementation of laboratory based surveillance to improve this. Injecting drug use is the single most important factor for the present hepatitis B transmission in Denmark, and IDUs poses a greater risk of HBV transmission to the general population than does immigrants. With few exceptions chronic infection reflects IDU or ethnic background. The failure of
Acknowledgements
The authors thank Lone Tønning-Sørensen for aliquoting sample material, supplying serology results and performing supplementary HBV serology. The survey was supported by financial grants from Odense University Hospital, University of Southern Denmark and Abbott Diagnostic division.
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