Chronic hepatitis B, chronic hepatitis C and chronic hepatitis (unknown cause) have been notifiable since 1998 in Estonia. Hospitals and family doctors notify laboratory confirmed acute cases of hepatitis B and C to the Estonian Health Protection Inspectorate (http://www.tervisekaitse.ee/tkuus.php). Notification of HCV infection, based on HCV antibody detection was first implemented in Estonia in 1991, and notification of hepatitis B started in the early 1980’s.

Trends in hepatitis B and C incidence
In Estonia, the average incidence of acute hepatitis B during the 1980s and early 1990s was 11.7 per 100 000 population (range 7.0-15.8) [1]. Incidence of HCV infection in the early and mid 1990s ranged from 0.4 to 4.4 per 100 000 population.

A large proportion of acute hepatitis infections are asymptomatic, and therefore the incidence is greatly underestimated [2]. There are no data on the proportion of asymptomatic cases in Estonia.

Table. Acute hepatitis B and C incidence in Estonia, by age, 1996-2003.

By 2001, the reported incidence of acute hepatitis B infection was 33 per 100 000 population: 2.9 times higher than in 1995. Acute hepatitis C affected 22 per 100 000 population in 2001, which was 4.7 times more than in 1995. However, 2002 and 2003 data showed a decline in incidences to 13 per 100 000 for acute hepatitis B, and 11 per 100 000 for acute hepatitis C.

Vulnerable populations
The incidence of HBV and HCV infections is highest among people aged 15-19 and 20-29 years, and higher among men than women. Injecting drug use is the most common risk factor for HBV and HCV in young people, accounting for more than half the new cases.

Several risk factors for HBV and HCV infection are well established. In Estonia, HBV and HCV transmission via blood transfusion and medical procedures has declined significantly during the last decade while risk factors other than transfusion were recognised as the most important. Currently, injecting drug use is the most common risk factor identified among youth, accounting for more than half of all new hepatitis cases for which there is data on likely transmission route. The route of transmission for approximately 40% of all cases remains unknown. It is often very difficult to determine the correct route of transmission, for example, sexual, through unhygienic tattooing or through unreported injecting of drugs - most often the latter.

Injecting drug users
Concurrent infections with multiple hepatitis viruses and other bloodborne pathogens such as HIV are common among injecting drug users (IDUs) in Estonia. Chronically infected IDUs are a major reservoir of HBV and HCV and may transmit the infections to the general population. A study of IDUs who visited anonymous HIV testing facilities found that 65% were seropositive for HBV and 95% for HCV. The co-infection rate was 65% [2].

In Estonia, the rapid increase in injecting drug use started in 1994-1995 and remains at a high prevalence which is now stable. There are an estimated 12 000-17 000 IDUs in the country who mostly use heroin. About 85% of them are Russian speaking and 75% are young men aged 15-25 years. As a result, the Russian speaking community is especially vulnerable to the spread of hepatitis B and C, as well as HIV infection [3]. The spread of viral hepatitis preceded the concentrated epidemic of HIV in 2000-2003 among IDUs in northeastern and northern Estonia [4,5]. The incidence rate of HIV infection remains the highest reported in Europe [6].

Prisoners
A large number of prisoners in Estonia are at risk of contracting hepatitis B and C infection as a result of sharing syringes while injecting drugs and unhygienic tattooing practices. It has been estimated that about 30% of Estonian prisoners are injecting drugs.

A study of 122 HIV positive IDUs at Tallinn Central Prison found that the prevalence of HBV antibodies was 89%, HCV antibodies 98% with both together at 89%. This was significantly higher than the prevalence in IDUs not in prison who visited anonymous HIV testing facilities.

A study of 237 HIV negative IDUs in prison indicated that the prevalence of antibodies to HBV and HCV in 1996-2000 was 82% and 94%, respectively. Eighty six per cent of HCV infected IDUs were found to have some marker of HBV infection. HBV and HCV infection was detected in 20% and 13% of self-declared non drug-dependent inmates (n=40) respectively [unpublished data, NIHD Virology Department].

Markers of current chronic HBV infection were detected among 8% of studied imprisoned IDUs, who were not clinically ill [7]. Data for chronic hepatitis C infection are not available.

Prevention and control measures
HBV vaccination is free of charge for some groups including healthcare workers (since 1997), adolescents aged 13 (since 1999) and newborns throughout the country (since 2003). Efforts to vaccinate adults (including IDUs and prisoners) have been limited, primarily due to the absence of sustainable programmes and the cost of the vaccine.

In 2002-2003, compliance to an accelerated schedule (at 0, 1 and 3 weeks), compared with the standard schedule (0, 1 and 6 months) for prophylactic hepatitis B vaccination among IDUs imprisoned in Tallinn Central Prison was investigated. The full vaccination course (three vaccinations) was administered to 457 IDUs (81%) of 566 inmates included in the study. The results revealed that a short hepatitis B vaccination schedule among imprisoned IDUs has a significantly higher compliance and seroprotection rate than the standard six month schedule, and should therefore be recommended for use in this population. Low seroprotection rate was correlated to concurrent hepatitis C infection [8]

Conclusion
Taking into account the current epidemiological situation for viral hepatitis in Estonia, there is an urgent need for preventive measures to be strengthened. Behavioural interventions to reduce the harm and risk of HBV/HCV infections, HBV vaccination, and appropriate medical management of chronically infected persons from the community at large and the IDU population could help to solve this serious public health problem in Estonia.

This article was adapted from reference 1 by the editorial team and Dr K Kutsar.