Detection of influenza virus and pathogens of acute respiratory viral infections in population of Kazakhstan during 2018-2019 epidemic season

Influenza and other acute respiratory viral infections are the most common infectious diseases of our time, causing a significant harm to human health as well as great economic damage. At least five groups of viruses, including more than 300 subtypes, are currently related to ARVI pathogens. Such infectious agents are characterized by a high degree of variability resulting in replaced virus antigenic characteristics augmenting their contagiousness, immunoevasion, and resistance to chemotherapeutic drugs. Of relevance, influenza and other ARVIs also pose a threat due to subsequent rapid formation of bacterially-associated respiratory diseases as well as their continuous variability and emergence of new pathogenic species. In recent years, subtype A (H1N1) and A (H3N2) with predominance of pandemic strain, as well as type B influenza viruses have been simultaneously found in circulation. Most common among the causative agents of noninfluenza ARVIs, are respiratory syncytial virus, rhino- and adenoviruses, as well as I/III parainfluenza viruses. Here we present the results of virological and serological studies of clinical samples collected during the 2018—2019 epidemic season in the territory of the Republic of Kazakhstan after analyzing 2794 clinical samples (2530 nasopharyngeal swabs and 264 blood serum samples) of patients diagnosed with ARVI, ARI, bronchitis, and pneumonia. Examining nasopharyngeal swabs by using RT-PCR showed that the mixed etiology influenza viruses with predominant A/H1N1pdm virus circulated in Kazakhstan. In particular, influenza virus genetic material was found in 511 swabs (20.20% of total examined samples), so that influenza A virus RNA was detected in 508 biological samples such as A/H1N1 — in 289, A/H3N2 — 209, unverified virus subtype — 10 samples. Type B influenza virus was detected in 3 samples. Analyzing 264 blood serum samples by the HAI assay and ELISA showed the presence of antibodies specific to influenza A/H1N1, A/H3N2, and B viruses in the population of various regions of Kazakhstan, thereby indirectly confirming their co-circulation. 42 influenza virus strains were isolated in chicken embryos, of which 28 were assigned to A/H1N1pdm virus, 13 — A/H3N2 virus, and one isolate was identified as influenza B virus. The laboratory diagnostics of clinical samples for ARVIs revealed that respiratory syncytial virus prevailed among identified non-influenza agents, whereas rhino- and adenoviruses were less common. Metapneumoviruses, bocaviruses, coronaviruses, and type I parainfluenza viruses were detected in few cases. Comparison of our study data with the data on 2017—2018 circulation of influenza pathogens showed that in Kazakhstan influenza A and B viruses continued to circulate, with the dominance of A/H1N1pdm virus as it was in the previous epidemic season. Identification of non-influenza viruses, the causative agents of 2018—2019 respiratory infections, showed the predominance of respiratory syncytial virus that correlated with the aforementioned results.