[Epidemiology of influenza A/California/07/09 (H1N1) in population of 49 cities in Russia in 2009 - 2010].

Aim: Comparison of influenza A(H1N1) epidemic in Russia caused by pandemic virus A/ California/07/09 (H1N1) in 2009 with previous epidemics of influenza A of this subtype.

Materials And Methods: Analysis of A/California/07/09 (H1N1) epidemic was carried out in 49 cities--bases of Federal center of influenza. Parameters of this epidemic by duration, influenza and acute respiratory viral illness morbidity, hospitalization and mortality rates from laboratory confirmed influenza in the population in general and in age groups (0 - 2 years, 3 - 6 years, 7 - 14 years, 15 - 64 years, 65 years and older) were studied.

Results: A/California/07/09 (H1N1) epidemic differed from the seasonal epidemics by unusually early onset, monoetiology, wide coverage of the population of cities, longer duration and higher morbidity in the population from 7 to 64 years of age, higher rate of hospitalizations and number of lethal outcomes in the population from 15 to 64 years of age. Lower morbidity, rate of hospitalizations and number of lethal outcomes was notable in individuals older than 65 years, that is an indication of the presence of an anamnestic immunity.

Conclusion: Comparative analysis of A/ California/07/09 (H1N1) epidemic with 3 previous influenza pandemics in Russia has shown, that during this epidemic population morbidity was 2 times lower than during 1957 and 1968 pandemics, and the rate approached that of the 1977 pandemic. This epidemic differed from previous pandemics by a delay of city-megapolis and preschool aged children involvement, early onset and lower intensity of peak; lower relative rate of morbidity among adult population and higher--among school children; higher multiplicity of excessive morbidity of children compared with morbidity of people older than 15 years.