Comparing Clinical Characteristics Between Hospitalized Adults With Laboratory-Confirmed Influenza A and B Virus Infection

We challenge the notion that influenza B is milder than in-fluenza A by finding similar clinical characteristics betweenhospitalized adult influenza-cases. Among patients treatedwith oseltamivir, length of stay and mortality did not differby type of virus infection.Keywords. influenza A and B virus infection; antiviraltreatment; hospitalization; adult.InfectionduetoinfluenzaBvirusisoftenperceivedtobemilderthan influenza A virus infection. However, studies have shownsimilar clinical features between patients infected with seasonalinfluenzaAandBvirusinoutpatientsettings[1,2]andsubstan-tial influenza B infections among pediatric influenza-associatedfatalities [3]. In addition, some studies have suggested thatoseltamivir may be less effective at reducing fever in outpa-tients infected with influenza B virus compared with influenzaAvirus[4]; very few published studies have compared out-comes among hospitalized patients, especially among adults.We used 8 years of data from adults hospitalized with labora-tory-confirmed influenza to compare clinical characteristicsbetween those infected with influenza A and B viruses and tocompare outcomes among patients treated with antiviral med-ications by virus type.METHODSWeuseddatafrom2005–2006through2012–2013influenzasea-sonscollected throughthe Influenza HospitalizationSurveillanceNetwork (FluSurv-NET), a partnership between the Centers forDiseaseControlandPrevention(CDC)andstateandlocalhealthdepartments, academic institutions, and their collaborators inmultiplestates.Priorto1September2009,thefollowing10stateswere included in surveillance: California, Colorado, Connecticut,Georgia,Maryland,Minnesota,NewMexico,NewYork,Oregon,and Tennessee.During 1September 2009–30 April 2010,thefol-lowing 5 additional states were included in surveillance: Iowa,Idaho, Michigan, Oklahoma, and South Dakota. After 1 October2010, California, Colorado, Connecticut, Georgia, Idaho, Mary-land,Michigan,Minnesota,NewMexico,NewYork,Ohio,Okla-homa,Oregon,RhodeIsland,Tennessee,andUtahwereincludedinsurveillance. FluSurv-NET conducts population-basedsurveil-lance for laboratory-confirmed influenza-associated hospitaliza-tions during the influenza season (ie, 1 October to 30 April forregular influenza season; the 2008–2009 season, however,ended on 14 April to account for the emergence of the influenzaA(H1N1)pdm09 virus in the spring of 2009; the 2009–2010 sea-son encompassed 15 April2009 through30 April2010). Patientswere captured in the surveillance system if they resided in theproject catchment area and were hospitalized in one of the sur-veillance hospitals with a positive influenza test result as deter-mined by viral culture, immunofluorescence antibody staining,rapid antigen test, reverse transcription polymerase chain reac-tion,ordocumentationofapositivetestresultinapatient’smed-ical record. Demographic and clinical information were obtainedfrom medical chart review. The analysis was limited to patientsaged ≥18 years and excluded possible nosocomial infections.In addition, we summarized influenza virus surveillance datafrom the World Health Organization (WHO) and National Re-spiratory and Enteric Virus Surveillance System collaborating