Abstract
This study aimed at assessing the frequency and the distribution of influenza virus types/subtypes in 172 laboratory-confirmed influenza-positive patients admitted to intensive care units (ICUs) during the 2017–2018 season in the Lombardy region (Northern Italy), and to investigate the presence of molecular pathogenicity markers. A total of 102/172 (59.3%) patients had influenza A infections (83 A/H1N1pdm09, 2 H3N2 and 17 were untyped), while the remaining 70/172 (40.7%) patients had influenza B infections. The 222G/N mutation in the hemagglutinin gene was identified in 33.3% (3/9) of A/H1N1pdm09 strains detected in the lower respiratory tract (LRT) samples and was also associated with more severe infections, whereas no peculiar mutations were observed for influenza B strains. A single-point evolution was observed in site 222 of A/H1N1pdm09 viruses, which might advantage viral evolution by favouring virus binding and replication in the lungs. Data from 17 paired upper respiratory tract (URT) and LRT samples showed that viral load in LRT samples was mostly higher than that detected in URT samples. Of note, influenza viruses were undetectable in 35% of paired URT samples. In conclusion, LRT samples appear to provide more accurate clinical information than URT samples, thus ensuring correct diagnosis and appropriate treatment of patients with severe respiratory infections requiring ICU admission.
Highlights
Influenza A and B viruses are transmitted efficiently from human to human and follow a seasonal epidemic pattern that in countries with temperate climates occurs mainly during winter [1]
The aims of this study were (i) to assess the frequency and the distribution of influenza virus types and subtypes in patients admitted to intensive care units (ICUs) during the 2017–2018 influenza season in the Lombardy region (10 million inhabitants) in northern Italy; (ii) to carry out molecular and phylogenetic analyses of the HA gene sequences of influenza A/H1N1pdm09, A/H3N2 and B viruses; (iii) to determine the epidemiological and molecular characteristics of influenza viruses in severe and mild respiratory infections in order to identify molecular pathogenicity markers
A total of 172 laboratory-confirmed influenza cases were observed among patients admitted to ICUs in the Lombardy region during the 2017–2018 season
Summary
Influenza A and B viruses are transmitted efficiently from human to human and follow a seasonal epidemic pattern that in countries with temperate climates occurs mainly during winter [1]. A viruses (namely subtypes H1N1pdm and H3N2) and influenza B viruses (lineage B-Yagamata and B-Victoria) are currently the cause of seasonal epidemics [1]. Seasonal influenza affects 5–10% of adults and 20–30% of children and is responsible for 3–5 million cases of severe illness and up to 650,000 deaths worldwide [2]. Most influenza cases are mild, some patients develop severe acute respiratory infections (SARIs) and acute respiratory distress syndrome (ARDS), requiring admission to intensive care units (ICU). While underlying clinical conditions play an important role in the pathogenesis of severe respiratory syndromes, some viral strains (such as A/H1N1pdm09) appear to significantly and independently contribute to the development of SARI and ARDS [3]. Since 2009, international health authorities have recommended the investigation of severe and complicated cases of influenza [4]. An annual seasonal influenza vaccination is recommended for pregnant women, the elderly, young children, immunocompromised people and people with chronic and cardiovascular disease who are at high risk of developing influenza complications [5]
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