Modern epidemiology of hepatitis A in the north-western region of the Russian Federation. 
The epidemiological features of hepatitis A virus (HAV) infection were studied in eleven territories located in the north-western region of the Russian Federation.  The dynamics of HAV infection in Russia and in the region were evaluated during a 17-year period.  The age-specific incidence was calculated and 229 305 patients with acute HAV were identified.  The analysed database included HA mixed with other viral hepatitis infections: it included information about 8 809 HAV patients.  Special attention has been paid to the sero-epidemiological studies conducted in St Petersburg city.  These studies included analysis of age-specific incidence in persons 20 years of age and older during 6 years and testing of blood sera from 1 892 healthy persons for IgG anti-HAV.  In general there is a trend to reduction of HAV incidence in Russia, and in the north-western region, high indices were registered in some provinces in different years.  It was established three types of age-specific incidence distribution: predominated incidence in 3-14 years of age (first type), 15-29 years of age (second type) and uniform distribution in different age groups (third type).  It was shown that decrease of HAV incidence in children and young adults lead to the reduction of sero-positivity level in the groups 20+ years of age.  These characteristics should be taken in account to define indications for HAV vaccine prophylaxis.  HAV infection in 10-13% of cases mixed with acute or chronic hepatitis B and C in the last 15 years in St Petersburg.  In the middle of 1990s, HAV mostly mixed with acute viral hepatitis of different aetiology, but in the modern time predominated type of mixture was presented by HAV and chronic HBV and HCV infections.  The obtained results are useful for viral hepatitis surveillance and control.