Hepatitis B in the family J. Milas 1 , D. Ropac 2 , R. Mulic 2 , V. Milas 3 , I. Valek 1 , I. Zoric 2 & K. Ko zul 1 1 Public Health Institute, Osijek, Croatia; 2 University of Split, School of Medicine, Department of Public Health, Croatia; 3 Osijek University Hospital, Osijek, Croatia Accepted in revised form 28 February 2000 Abstract. During a 3-year period (1992±1995), 239 index cases of hepatitis B virus (HBV) infection and 459 members of their households from the Osijek- Baranja county were examined. The aim of the study was to determine the spread of HBV infection in the families with a member veri®ed as a virus carrier, and to identify the family members with the highest risk of infection according to kinship de- grees. The retrospective and prospective methods were used in the study. The probable route of in- fection was assessed by the use of an epidemiologic questionnaire, and the serologic status of the study subjects concerning infection with HBV was deter- mined by enzyme immunoassays (HBsAg, anti-HBs, anti-HBe and anti-HBc). The ®rst member of a family identi®ed as a virus carrier was considered an index case. HBV infection was demonstrated in 334 (47.85%) out of a total of 698 subjects. Only 21 (6.28%) of the 334 subjects with veri®ed HBV infection developed the clinical picture of acute hepatitis B. The ratio of clinically manifest vs inapparent infection was 1:16. Serologic traces of infection were detected in 95 of the 459 family members of the index cases, yielding a mean rate of the infection among the virus carrier family mem- bers of 20.70%. Key words: Family, Hepatitis B virus (HBV) infection Introduction The prevalence of hepatitis B virus (HBV) infection in Croatia has not yet been precisely determined. Some studies suggest it to be rather low (<2%) [1], whereas others believe that Croatia belongs to regions with a moderate prevalence of HBV infection (2±7%) [2, 3]. About 200 cases of acute, clinically manifest hepatitis B are recorded in Croatia every year [4]. The number of subjects with ®rst ever infection per year and of those with chronic liver diseases related to HBV infection is as yet unknown in Croatia [1]. The routes of HBV infection transmission vary according to particular population groups. Blood is the predominant route of infection, and all body ex- creta and secretion are also infectious. Sexual contact is one of the main routes of HBV infection trans- mission in a low-endemic population [1±3]. The dis- semination of HBV infection is also eected by very close, non-sexual contact (saliva, blood) with the in- fected person. Seroepidemiologic studies have proved the relatively frequent HBV infection transmission from a HBV infected person to the members of the same household [5±9]. The clinically manifest disease due to such a route of infection transmission is quite rare. The real routes of transmission in these inter- familial contacts are manifold and common (e.g., use of a common shaver, tooth brush and towels, super®cial injuries and skin infections, etc.) [2, 8, 9]. Generally, the population groups at risk include medical personnel, homosexuals, prostitutes and promiscuous individuals, intravenous drug addicts and mentally retarded persons [1±4, 8±11]. Material and methods Data on the individuals with HBV infection were collected from reports of the epidemiologic service of the Public Health Institute of the Osijek-Baranja county, and from reports on HBV infected blood donors of the Blood Transfusion Department, Osijek University Hospital, recorded during the 1992±1995 period. These individuals were designated as index cases, i.e. they were considered to have transmitted the infection to the family, although subsequent epi- demiologic studies failed to con®rm such a sequence of events in each of the cases. These individuals were the stimulus for the study of HBV infection in other members of the family or household. The index cases were asked about risk factors for the last 8 years. The sera of all study subjects, including index cases and their family members, were tested for the HBV infection markers, i.e. HBsAg, HBeAg, anti-HBs, anti-HBc and anti-HBe. The sera were examined by enzyme immunoassays using Organon tests. All study subjects were asked to ®ll out a questionnaire on general data, results of serologic analysis, kinship to European Journal of Epidemiology 16: 203±208, 2000. Ó 2000 Kluwer Academic Publishers. Printed in the Netherlands.