[Etiology of influenza according to the data of serological diagnostics in hospital patients in St. Petersburg at the period of 1968 - 2000].

The specific features of the etiology of influenza in children and adults at the period of the simultaneous circulation of two subtypes of influenza virus A, according to the results in the hemagglutination-inhibition reaction in 261,490 influenza and ARD patients hospitalized in St. Petersburg in the course of 32 years, were analyzed. The results of serological diagnostics was shown to correspond to the data of the identification of influenza viruses in Russia and all over the world. At the period of epidemics diseases caused by the main infective agents of the epidemics were detected in 11.0% - 51.0% of cases and by concomitant infective agents, in 0.6% - 12.4% of cases. After the reappearance of influenza virus A(H1N1) in circulation higher frequency of mixed forms of infection and the presence of competition between the subtypes of influenza virus A was noted. In young children a decrease in differences in the proportion of influenza cases, caused by the main and concomitant infective agents, as well as between the detection of influenza in epidemic and in summer periods, was registered.