Epidemiological data show significant increase of influenza activity in Russia in comparison with previous week. The nationwide ILI & ARI morbidity level (134.3 per 10 000 of population) exceeded the national baseline (69.5 per 10 000) by 93.4%.
ILI and ARI epidemic thresholds were exceeded in 47 of 59 cities collaborating with two WHO NICs in Russia.
Laboratory diagnosis data. Results of influenza laboratory diagnosis by different tests were submitted by 53 RBLs and two WHO NICs. According to these data as a result of 9882 patients investigation the overall proportion of respiratory samples positive for influenza virus was estimated as 3523 (35.7%) including 3248 (92.2%) influenza A(H1N1)pdm09 cases, 118 (3.3%) influenza A(H3N2) cases, 130 (3.7%) influenza A cases and 27 (0.8%) influenza B cases.
Influenza and ARI morbidity data. Influenza activity increased significantly on the week 05.2016. The nationwide ILI & ARI morbidity level (134.4 per 10 000 of population) exceeded the national baseline by 93.4%.
Etiology of ILI & ARI morbidity. As a result of investigation of 9882 patients in 53 cities of Russia the overall proportion of respiratory samples positive for influenza in traditional surveillance system was estimated as 35.7%. Influenza A(H1N1)pdm09 dominated (92.2% of influenza cases). Influenza A(H3N2) and B cases registered sporadically.
In sentinel surveillance system clinical samples from 95 SARI and 83 ILI/ARI patients were investigated by rRT-PCR. 43 (45.3%) influenza cases including 42 influenza A(H1N1)pdm09 and 1 influenza B cases were detected among SARI patients and 37 (44.6%) influenza cases including 35 influenza A(H1N1)pdm09 and 2 influenza A(H3N2) cases were detected among ILI/ARI patients.
Antigenic characterization.
Totally 108 influenza A(H1N1)pdm09, 2 influenza A(H3N2) and 5 influenza B viruses were characterizated antigenically in two NICs of Russia since the beginning of the season. According to St.Petersburg NIC data 6 influenza A(H1N1)pdm09 strains were related closely to influenza A/California/07/09 virus. Most of 102 influenza A(H1N1)pdm09 viruses investigated in Moscow NIC were similar to vaccine A/California/07/09 virus however 10 of them had decreased up to 1/16 titer in interaction with antiserum to this virus. Two A(H3N2) strains were similar to influenza A/Hong-Kong/5738/2014 virus, with antiserum to influenza A/Switzerland/9715293/2013 they reacted up to 1/4 - 1/8 of homological titer in HI. All investigated 5 influenza B viruses belonged to Victorian limeage and were similar to influenza B/Brisbane/60/2008 reference strain reacting with antiserum to this virus up to 1/4 - 1/8 of homological titer in HI.
Genetic characterization. 55 investigated influenza A(H1N1)pdm09 virus strains were A/South Africa/3626/2013-like. All viruses bear clade 6B specific mutations in HA (S84N, S162+N and I216T) and formed new genetic group according to phylogenetic analysis. Two A(H1N1)pdm09 sequences obtained directly from autopsy sample showed the presence of additional mutation D222G in HA1.
