The main objective of the study was to evaluate neuraminidase inhibiting (NI) antibodies against A/H1N1pdm09 influenza viruses in the community as a whole and after infection. We evaluated NI serum antibodies against A/California/07/09(H1N1)pdm and A/South Africa/3626/2013(H1N1)pdm in 134 blood donors of different ages using enzyme-linked lectin assay and in 15 paired sera from convalescents with laboratory confirmed influenza. The neuraminidase (NA) proteins of both A/H1N1pdm09 viruses had minimal genetic divergence, but demonstrated different enzymatic and antigenic properties. 5.2% of individuals had NI antibody titers ≥1:20 against A/South Africa/3626/2013(H1N1)pdm compared to 53% of those who were positive to A/California/07/2009(H1N1)pdm NA. 2% of individuals had detectable NI titers against A/South Africa/3626/13(H1N1)pdm and 47.3% were positive to A/California/07/2009(H1N1)pdm NA among participants negative to hemagglutinin (HA) of A/H1N1pdm09 but positive to seasonal A/H1N1. The lowest NI antibody levels to both A/H1N1pdm09 viruses were detected in individuals born between 1956 and 1968. Our data suggest that NI antibodies against A/South Africa/3626/13 (H1N1)pdm found in the blood donors could have resulted from direct infection with a new antigenic A/H1N1pdm09 variant rather than from cross-reaction as a result of contact with previously circulating seasonal A/H1N1 variants. The immune responses against HA and NA were formed simultaneously right after natural infection with A/H1N1pdm09. NI antibodies correlated with virus-neutralizing antibodies when acquired shortly after influenza infection. A group of middle-aged patients with the lowest level of anti-NA antibodies against A/California/07/2009 (H1N1)pdm was identified, indicating the highest-priority vaccination against A/H1N1pdm09 viruses.

Etiology of respiratory virus infections among 1699 hospitalized patients (HP) was determined by PCR during the period of increased influenza activity in 2012 - 2013 season. The rate of accidence of influenza virus in dependence of gender, age, social and demographic factors and previous vaccination was analysed. Young children dominated in the age structure of HP, while the elderly were hospitalized very rarely. According to results obtained rate of influenza detection in HP was significantly higher among adults in comparison with children (63,5 and 30,7% of investigated patients, correspondingly). Respiratory syncytial virus and rhinoviruses were detected the most regularly (8.7 and 3.1%, correspondingly) in children, parainfluenza and adenoviruses were registered rarely (1.4 and 2.1%, correspondingly). Rate of detection of coronaviruses and bocavirus was low and varied in the range 0.3 - 0.6%. Indicated above ARI agents among hospitalized adults were detected rarely (0 - 1.5%) with exception of RSV which was detected among elderly (75 - 84 years) in 5.9% cases. No metapneumovirus cases were detected among HP in indicated period. Although males dominated (58%) among HP influenza cases, regardless of the type/subtype, were registered more frequently among girls in comparison with the boys of the same age groups. Influenza cases were registered more frequenly as well among smoking than in not smoking patients. Young children dominated in the age structure of HP, while the elderly were hospitalized very rarely.

ФГБУ «Научно-исследовательский институт гриппа» Минздрава России, 197376, г. Санкт-Петербург В работе изучена этиологическая структура гриппа и других ОРВи в Санкт-Петербурге и Ленинградской области, установлена их доля в течение 4 эпидемических сезонов. Показана сезонность некоторых респираторных вирусов и обозначены пики циркуляции респираторно-синцитиального (РС) вируса, аденовируса, вирусов парагриппа, риновируса, бокавируса, метапневмовируса и коронавируса. Прослежено взаимовлияние вирусов гриппа А и РС-вирусов, РС-вирусов и риновирусов. Выявлен высокий уровень заболеваемости аденовирусной инфекцией в организованных коллективах и РС-вирусной инфекцией у детей. К л ю ч е в ы е с л о в а: вирусы гриппа; острые респираторные вирусные инфекции; ПЦР-диагностика; эпидемический сезон. The etiological structure of influenza and other acute respiratory viral infections including their rate of incidence in St. Petersburg and Leningrad region during 4 epidemic seasons has been studied. Seasonality of some respiratory viruses was shown and peaks of circulation of RSV, adenovirus, parainfluenza viruses, rhinovirus, bocavirus, metapneumovirus and coronavirus were marked. The interference of influenza A viruses and RSV, RSV and rhinoviruses was highlighted. A high incidence of adenovirus infection in organized communities and RSV infection in children was revealed. K e y w o r d s: Influenza viruses; acute respiratory viral infections (ARVI); PCR diagnostics; epidemic season. For citation: Pisareva M.M., Eder V.A., Buzitskaya Zh.V., Musaeva T.D., Afanaseva V.S., Go A.A., Obraztsova E.A., Sukhovetskaya V.F., Komissarov A.B. Etiological structure of influenza and other ARVI in St. Petersburg during epidemic seasons Information about authors: Pisareva M.M., http://orcid.org/0000-0002-1499-9957Eder V.A., http://orcid.org/0000-0002-9970-3325 Buzitskaya Zh.V., http://orcid.org/0000-0002-8394-102X Musaeva T.D., https://orcid.org/0000-0002-3050-1936 Afanasieva V.S., http://orcid.org/0000-0002-2887-0126 Sukhovetskaya V.F., http://orcid.org/0000-0002-1566-7137 Komissarov A.B., http://orcid.org/Для корреспонденции: Писарева Мария Михайловна, канд. биол. наук, ведущий научный сотрудник лаборатории молекулярной вирусологии ФГБУ «НИИ гриппа» Минздрава России, 197376, г. Санкт-Петербург.

In this paper, we analyze the etiology of the diseases occurring during two consecutive influenza epidemic seasons in St. Petersburg, Russian Federation. The analysis is based on the results of the PCR diagnostics of the clinical samples collected from patients hospitalized in three St. Petersburg hospitals with influenza like illnesses (ILI). It was shown that the influenza virus A(H1N1)pdm09 was the dominant causative agent during the 2012-2013 epidemic season while, in the 2013-2014 season, A(H3N2) virus was predominant among adults and children. The influenza B virus activity was high in the 2012-2013 season and low in the 2013-2014 season. During both seasons, the main causative agent for the hospitalization of young children was respiratory syncytial virus (RSV), followed by rhinovirus and influenza virus. The rate of involvement of parainfluenza, adenovirus, metapneumovirus and coronavirus was low and was negligible for bocavirus. Children 0-2 and 3-6 years old formed the group of patients that was affected by acute respiratory infection agents the most. Children younger than 3 months old were the major group of the intensive care unit (ICUs) patients and only 27.5% of them were adults. RSV and rhinovirus were the leading cause of ILI among the children admitted to ICU. Among the adult patients admitted to the ICU, only influenza A(H1N1)pdm09, A(H3N2) and B viruses were detected during both influenza seasons.According to the results of the antigenic and genetic analysis, most influenza A(H1N1)pdm09 and A(H3N2) viruses circulating in St. Petersburg matched the vaccine strains recommended by the WHO for vaccine composition in the

The aim of this study was to compare the results of the hemagglutination inhibition test (HI-test) and microneutralization reaction in detection of antibodies to influenza A(H1N1), A(H1N1)pdm09, and A(H3N2) viruses in human sera, as well optimize microneutralization reaction conditions. The proposed variant of microneutralization reaction is based on detecting decreased influenza virus reproduction in infected MDCK cells in the presence of virus-specific serum antibodies. Virus reproduction was evaluated by enzyme-linked immunosorbent assay in 96-well cell culture plates using type-specific anti-influenza A viruse NP-protein monoclonal antibodies. In parallel, in microneutralization reaction and HI-test paired sera collected from 205 volunteers inoculated with inactivated seasonal influenza vaccines were analyzed, as well as from 117 adult patients with laboratory-confirmed influenza. The rationale for treatment of human serum with receptor-destroying enzyme (RDE) was proved not only for HI-test, but also for microneutralization reaction. Compared to HI-assay, the microneutralization reaction displayed higher sensitivity. According to microneutralization data, seroconversion rates and increase in antibody titer against influenza A viruses in both vaccinated and infected persons were superior to HI-test data by 1.4–2.5-fold. Moreover, higher sensitivity of this method was of great importance for the diagnostics of disease caused by new pathogens. The efficacy of influenza A(H1N1)pdm09 serodiagnostics in PCRpositive patients was 1.5 times higher based on microneutralization reaction vs. HI-assay data. According to the data from early studies, it is commonly believed that 1/40 titer of flu-specific antibodies detected by HI-test is set as protective. However, a consensus on protective level for virus-specific antibodies in neutralization reaction has not been established yet. It was found that serum antibody levels detected by the proposed version of microneutralization reaction were significantly higher than those in HI-assay. In the post vaccination sera collected from vaccinated volunteers, average titers of virus neutralizing antibodies corresponding to 1/40 in HI-test were 1/195, 1/203, and 1/ 426–1/430 for influenza A(H1N1), A(H1N1)pdm09 and A(H3N2), respectively, whereas in influenza patients they were 1/285, 1/215 and 1/488, respectively. Thus, it was suggested to consider a threshold value for “conditionally protective” level of neutralizing antibodies in adult vaccinated volunteers or infected patients, an average titer 1/160 for A(H1N1) and A(H1N1)pdm09 viruses, as well as 1/320 — for A(H3N2) virus, which agree with data published elsewhere.