Molecular characterization of Influenza strains circulated in patients admitted to ICU during the 2017-18 season in Italy

Background: The 2017/18 influenza season has been characterized by the uncommon early high rate circulation of influenza B virus. In fact, based on epidemiological surveillance data of ECDC the majority of influenza viruses detected were type B (63%), representing a high level of circulation of influenza B viruses compared to recent seasons [1]. Material and Methods: A total of 764 influenza laboratory-confirmed cases in ICUs patients have reported in Italy during the last influenza season and 172 (22.5%) of them occurred in Lombardy region. The typing of Influenza positive samples (A and B strains) and sequencing of HA gene were performed as previously described [2,3]. Results: Eighty-three out of 172 (48.3%) cases were typed as A/H1N1pdm09, 71 (41.3%) as influenza B, 1 (0.6%) as influenza A/H3N2 and from 10 (20.2%) no typing results were obtained. HA sequencing was performed for 58/83 (69.9%) influenza A and 33/71 (46.5%) influenza B strains. Forty-two (72.4%) Influenza A/H1N1pdm09 strains were characterized by the T120A change as observed. Overall, mutations (G/N/A) at codon 222 were observed in 5/58 (8.6%) influenza A/H1N1pdm09 strains. All influenza B strains belonged to the B/Phuket/3073/2013 clade and were characterized by L172Q and M251V changes. Conclusions: Un upsurge of influenza B cases in patients admitted to ICU with a severe respiratory infections has been observed during the last influenza season. No molecular signatures associated with increased severity were observed among Influenza B strains. On the contrary, Influenza A/H1N1pdm09 virus strains harbored, also in samples of URTI, the more aggressive 222G/N mutations. References: [1] https://ecdc.europa.eu/en/publications-data/weekly-influenzaupdate-week-20-may-2018 (last access 05 June 2018) [2] Piralla A, Lunghi G, Ruggiero L, Girello A, Bianchini S, Rovida F, Caimmi S, Marseglia GL, Principi N, Baldanti F, Esposito S. Molecular epidemiology of influenza B virus among hospitalized pediatric patients in Northern Italy during the 2015-16 season. PLoS One. 2017 Oct 19;12(10):e0185893. [3] Piralla A, Rovida F, Girello A, Premoli M, Mojoli F, Belliato M, Braschi A, Iotti G, Pariani E, Bubba L, Zanetti AR, Baldanti F. Frequency of respiratory virus infections and next-generation analysis of influenza A/H1N1pdm09 dynamics in the lower respiratory tract of patients admitted to the ICU. PLoS One. 2017 Jun 7;12(6):e0178926.