Circulation of influenza viruses in the epidemic season of 2018–2019 among people residing in Northern and Western Kazakhstan

Objective. Detection of influenza viruses among the population on the territory of the Northern and Western Kazakhstan during the 2018–2019 epidemic season. Patients and methods. The study involved 835 patients with ARVI symptoms. Biological samples were screened in real-time polymerase chain reaction (RT-PCR), hemagglutination inhibition (HAI) assay, and enzyme-linked immunosorbent assay (ELISA). Hemagglutinating agents were isolated in 9-10-day-old developing chicken embryos. Identification of isolates was carried out in RT-PCR and HAI assay. Results. 936 clinical samples (835 nasopharyngeal swabs and 101 blood serums) were collected from patients in the Northern (North Kazakhstan and Pavlodar oblasts) and Western (West Kazakhstan oblast) regions during the 2018–2019 epidemic season. Primary screening of 835 nasopharyngeal swabs revealed the genetic material of influenza virus in 20.48%, influenza A virus in 20.36%, and influenza B virus in 0.12%. Subtyping of PCR positive samples for influenza type A virus showed the presence of the genetic material of influenza A/H1N1pdm09 virus in 14.01%, A/H3N2 virus in 4.91%. The virus subtype was not established in 1.66%. Virological examination of nasopharyngeal swabs led to obtaining 14 isolates, of which 13 were identified as influenza A/H1N1pdm09 viruses and 1 as influenza A/H3N2 virus. Serological studies of 101 blood serums in the HAI assay showed the presence of antihemagglutinins against influenza A/H1N1pdm09 virus in 28.71%, A/H3N2 virus in 30.69%, type B virus in 3.96% of the total number of samples. Antibodies simultaneously against two subtypes of influenza viruses (A and B) were detected in 12.87% of cases. In ELISA antibodies against influenza A/H1N1 virus were revealed in 24.75% of cases, A/H3N2 virus in 19.80%, type B virus in 14.85%. Antibodies simultaneously against two types of influenza viruses (A and B) were detected in 2.97% of blood serums. Conclusion. The results of virological and serological studies presented in the paper suggest circulation of influenza A/H1N1pdm09, A/H3N2, and type B viruses in the examined oblasts of Kazakhstan during the 2018–2019 season. Key words: virus, hemagglutinin, influenza, diagnosis, isolate, neuraminidase, circulation