Hepatitis A seroprevalence in Slovene travellers

Hepatitis A virus (HAV) infection rates used to be very high in the past [1]. In the economically developed countries, HAV infection rates and the proportion of people with immunity to HAV decreased as a result of improved sanitation [2, 3]. There is a scarcity of information on the prevalence rates of anti-HAV in the Central European countries [4, 5]. Travellers to non-industrialized areas are exposed to infections that do not exist, or occur very rarely in their home country, such as HAV infection [6]. Nonimmune persons are effectively protected against HAV infection by timely vaccination. Immunization is not required in HAV seropositive travellers. The purpose of the study was to ascertain the seroprevalence of antibodies to HAV in adult Slovene travellers, and to determine whether prevaccination screening can reduce unnecessary vaccination. From the beginning of July 1999 to the end of October 1999, screening for antibodies to HAV was offered to all travellers aged 18–57 years who presented for immunization or malaria chemoprophylaxis at the travel clinic of the Institute of Public Health. The study included travellers born in Slovenia who had had no previous vaccination against HAV and denied having had known HAV infection. They were notified of test results. The travellers were categorized by the year of birth into the following eight groups: 1942–1946, 1947–1951, 1952–1956, 1957–1961, 1962–1966, 1967–1971, 1972–1976, 1977– 1981. On the basis of the ascertained seroprevalence we determined at what age prevaccination screening for HAV antibodies is cost-effective. Costs of the primary vaccination and booster immunization at months 6–12 were estimated. The total cost, i.e. the price of HAV vaccine plus the cost of vaccination, amounted to 97.8 EUR. The cost of antibody test was estimated to be 28.2 EUR. Over a period of 4 months, we tested 328 travellers (178 men and 150 women) with no history of acute HAV infection or previous vaccination against HAV. Altogether 103 (31.4%) subjects tested positive for HAV antibodies. Seropositivity rates are presented in Table 1. Seropositivity increased with age (p-value 0.001, v-test). Among the travellers born before 1962, 55.6% tested positive for anti-HAV. In contrast, a vast majority of persons (93.7%) born in 1971 and later who gave no history of infectious jaundice showed no immunity to HAV. Our observations are comparable to the results of a similar American study of travellers with no history of hepatitis A before vaccination [7]. It showed that solely 16.6% of persons born in industrialized countries were seropositive for HAV. The HAV seroprevalence rate was higher (32.1%) in individuals travelling frequently to economically less developed countries, and extremely high (82.7%) in people born in nonindustrialized countries. Prevaccination screening is considered cost-effective when the cost of vaccinating the entire population is higher than the cost of testing plus the cost of vaccinating non-immune individuals [8]. Considering the cost of vaccination of 97.8 EUR and 28.2 EUR for testing, the screening is economically valid for a population with a seropositivity rate of 29 per cent. The calculation based on the price of vaccine and cost of testing showed that vaccination without previous testing is cost-effective in subjects born after 1961. As previously mentioned, hepatitis A has become rare in the central part of Europe, too [4, 5]. The number of notified hepatitis A cases in Slovenia has been on a constant decline, particularly since 1990 (Figure 1) [9]. The decline is not attributable solely to the changed notification system, because the reporting