Circulation of influenza A viruses among patients hospitalized for severe acute respiratory infection in a tertiary care hospital in Romania in the 2018/19 season Results from an observational descriptive epidemiological study

The seasonal circulation of influenza viruses and the impact that this infection has on the population varies from year to year. We have prospectively captured hospital-based surveillance data describing the circulation of influenza viruses and characterizing patients with influenza admitted to a tertiary hospital in Bucharest, Romania in the 2018/19 season. We have conducted an observational descriptive epidemiological study analyzing all consecutive patients hospitalized for influenza like illness or severe acute respiratory infection at the National Institute for Infectious Diseases "Prof. Dr. Matei Bals", Bucharest, Romania, from November 2018 to April 2019. For all patients we actively collected standardized clinical information and performed real-time reverse transcription polymerase chain reaction testing of respiratory samples to identify the presence of influenza viruses and to determine the subtype/lineage. A total of 1128 hospitalized patients were tested in this study, with an influenza positivity rate of 41.2% (n = 465). We identified an exclusive circulation of influenza A viruses (A/H1 - 57.2%, A/H3 - 29.3%, A not subtyped - 13.3%), with only 1 case of influenza B detected at the end of the season (week 18/2019). Children under 5 years of age accounted for the majority of cases (40%, n = 186), and all cases had a favorable evolution. Females were more likely to test positive for influenza (53.3%) compared to males (46.7%), P = .048, and presence of asthma or chronic obstructive pulmonary disease increased the risk of influenza 4.4-fold and 2-fold, respectively (P P = .034). Thirteen influenza patients required hospitalization in intensive care and 5 deaths were recorded (1.1%). The vaccination rate for all patients included in the study was low (4.6%). The existence of chronic conditions or age over 65 years prolonged the hospitalization period with 2 days (P < .001 each). In the 2018/19 season, we identified an important circulation of influenza A viruses among patients hospitalized for influenza like illness/severe acute respiratory infection in a tertiary care hospital in Romania, with a higher likelihood of affecting females and patients with pre-existing lung conditions. Monitoring of the clinical and epidemiological characteristics of influenza virus infection is of great interest and should be done carefully each season to better inform on the necessary measures to limit the impact that this infection may have on risk groups.