The genotypes of 149 HCV strains from St. Petersburg were determined by limited sequencing and phylogenetic analysis within the NS5B region. One hundred two strains derived from patients that attended infectious disease clinics, of whom 48 admitted injecting drug use, and 47 derived from dialysis patients. Subtype 3a was predominant in the patients from infectious disease clinics, both in patients that admitted injecting drug use (56%) and in those with unknown source of infection (46%). However, 89% of the strains from dialysis patients belonged to subtype 1b. Eleven of twelve characterised strains from recent cases of hepatitis C at these units were at phylogenetic analysis shown to be related to strains already circulating there, demonstrating that within the dialysis units nosocomial transmission is the most important route of HCV infection. The predominance of subtype 1b strains in dialysis patients indicates that these strains have been circulating for a long time in dialysis units. The predominance of subtype 3a also among patients who did not admit drug use and that their strains were intermixed with the strains from injecting drug users in the phylogenetic analysis shows that the increase in injecting drug use is the major factor that explains the recent spread of HCV in the St. Petersburg population. This supports the concept that injecting drug use remains the major route for HCV infection in developed countries and that the control of drug abuse is the most important measure to prevent its spread.

summary. Hepatitis B (HB) is thought to be an expanding health problem in Russia. The incidence of infection was estimated from mandatorily reported HB cases in St Petersburg. The two‐sided t‐test for independent samples and the LOESS (locally‐weighted regression) smoother were used to compare the age at infection for symptomatic, asymptomatic and chronic infections, by gender. The force of infection was estimated from seroprevalence data (907 sera taken in 1999) using a newly developed nonparametric method based on local polynomials, as well as an earlier method based on isotonic regression and kernel smoothers. With the local polynomial method, pointwise confidence intervals (95%) were constructed by bootstrapping. On average, men contracted HB infection at a significantly younger age than women (in 1999, 21.8 vs 22.7 years, respectively). The overall male to female ratio was 1.92. In 1999 the overall incidence almost doubled compared with the preceding years and tripled among the age groups with highest incidence (15–29‐year olds: 85% of cases in 1999). The incidence increase was associated with a lower average age at infection (24.1 years in 1994 vs 22.1 years in 1999). The age and gender‐specific force of infection estimates generally confirmed the incidence estimates and emphasized the usefulness of local polynomials to do this. Hence HB transmission in St Petersburg occurs mainly in young adults. The dramatic increase of infections in 1999 was probably due to injecting drug use. Without intervention, HB virus is expected to continue to spread rapidly with a greater proportion of female infections caused by sexual transmission. These trends may also provide an indication for HIV transmission.

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.

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