Clinical Features Of Severe Influenza Pneumonia And Characteristics Of HA And NA Genes Of Influenza A(H1N1)pdm09 In Zhejiang Province

ObjectiveTo study the clinical features of severe influenza pneumonia and the characteristics of HA and NA genes of influenza A(H1N1)pdm09 in Zhejiang Province.Methods1.A retrospective,multicenter study was conducted in Zhejiang province through August 2017 to May 2018.Patients hospitalized with laboratory confirmed influenza and developed severe pneumonia were enrolled.Risk factors,effects of antiviral treatments and causative pathogens on secondary infection were analyzed.Statistical data were analyzed by SPSS v22.0.2.Influenza A(H1N1)pdm09 positive samples were collected from August 2017 to May 2018 in the First Affiliated Hospital,Zhejiang University School of Medicine.Clinical information was collected and patients were divided into severe pneumonia group,mild pneumonia group and non-pneumonia group for comparison.Hemagglutinin(HA)and neuraminidase(NA)genes of influenza A(H1N1)pdm09 were amplified by RT-PCR and genes were sequenced.Sequence alignment and homology analysis were performed by DNAStar v7.2.TREESUB,RAxML v8.2 and PAML v4.9 were used to construct phylogenetic trees.Results1.A total of 5820 hospitalized influenza cases were reported from August 2017 to May 2018 in 14 cooperative hospitals,including 248(4.3%)severe influenza pneumonia and 99(1.7%)deaths.A minor peak of hospitalization of influenza was observed in August to September,2017 and it finally peaked in January to February,2018.Logistic regression analysis showed that hemoptysis(OR 6.537;95%CI:1.185-35.953;P=0.031),,septic shock(OR 14.863;95%CI:5.072-43.551;P<0.001),ARDS(OR 3.577;95%CI:1.417-9.026;P=0.007)and increased WBC count(OR 1.104;95%CI:1.025-1.190;P=0.009)were the risk factors of death while neuraminidase inhibitor(NAI)treatment was a protective factor(OR 0.067;95%CI:0.006-0.803;P=0.033).2.Survival analysis showed that 60-day survival rate of patients with NAI treatment was significantly higher than those without NAI treatment(63.0%vs.7.7%,P<0.001).The 60-day survival rate of patients treated with double-dose oseltamivir(300 mg/d)was significantly higher than those with single-dose oseltamivir(150 mg/d)(68.3%vs.54.4%,P=0.025).No significant differences of 60-day survival rate were found between oseltamivir,peramivir monotherapy and oseltamivir-peramivir combination therapy as well as between different doses of peramivir treatment.3.A total of 63(25.4%)patients developed secondary infection,which usually occurred after 2-3 weeks after illness onset.Acinetobacter baumannii(47.6%),Aspergillus spp.(20.6%),Klebsiella pneumoniae(17.5%)and Staphylococcus aureus(11.1%)were the most frequently detected pathogens.Resistant pathogens accounted for 57.1%.4.As compared to vaccine strain A/Michigan/45/2015,the nucleotide and amino acid similarity of HA and NA genes of influenza A(H1N1)pdm09 in three groups were both equal or greater than 98%.HA gene phylogenetic analysis showed that all virus in our study belonged to 6B.1A.Majority of the virus in severe pneumonia group were concentrated in the same subclade(HA S183P),while the mild pneumonia group and the non-pneumonia group were scattered in different subclades.5.Influenza A(H1N1)pdm09 HA gene analysis showed that the rate of D222G/N/S variants was 23.1%in severe pneumonia group while it was not detected in mild pneumonia group and non-pneumonia group.The difference between severe pneumonia group and mild pneumonia group(P=0.010),as well as pneumonia group and non-pneumonia group(P=0.004)was significant.6.Influenza A(H1N1)pdm09 NA gene analysis showed that the rate of H275Y variants was 14.0%in severe pneumonia group while it was not detected in mild pneumonia group and non-pneumonia group.And the difference between pneumonia group and non-pneumonia group was statistically significant(P=0.038).Conclusions1.The mortality rate of severe influenza pneumonia was high.Hemoptysis,septic shock,ARDS and increased WBC count were the risk factors of death and close attention should be paid.2.Patients with severe influenza pneumonia should be treated with NAI therapy promptly.Double-dose oseltamivir treatment could be applied if necessary.3.In patients with severe influenza pneumonia,secondary infection appeared to occur in 2-3 weeks after illness onset.The pathogen composition was diverse and the proportion of drug-resistant pathogen was high.We recommend that bacterial and fungal cultures should be carried out in timely among these patients.4.Influenza A(H1N1)pdm09 HA D222G/N/S variants of receptor binding site and NA H275Y variants of drug resistance site were related to severe influenza pneumonia.Surveillance on these special variations should be carried out.