Influenza A(H1N1)pdm 2009 and influenza B virus co-infection in hospitalized and non-hospitalized patients during the 2015-2016 epidemic season in Israel

- Characterization of unusually high number of patients co-infected with influenza A (H1N1)pdm 2009 and influenza B viruses during the 2015-2016 influenza season in Israel.
- During the past 15 years we have not witnessed such prevalence of double infections and the reports on such events are scares.
- The unusually high number of patients dually infected with these two viruses encourages continuously monitoring this observation and raising the importance of evaluating the influenza virus strains present in the vaccine cocktail.
- In this report the clinical presentation of the immunocompetent patients dually infected with influenza A (H1N1)pdm 2009 and influenza B viruses did not differ from patient infected with either of the two viruses.
- Unlike other recent reports the majority of the influenza double infection occurred in the population and they will not nosocomial/health care associated infections.

BackgroundInfluenza A and B viruses co-infections are rare events and mainly occurred in immunocompromised patients.ObjectivesIn this study we report an unusually high occurrence of influenza A (H1N1)pdm 2009 and influenza B virus co-infections during the epidemic year 2015-2016.Study designNasopharyngeal swabs were collected from 1919 patients visiting 26 outpatient clinics distributed throughout Israel and presenting with influenza-like illness. In addition, hospitalized patient tested for influenza viruses were also included in the study. Patients samples collected between October 2015 and April 2016 were tested for the presence of influenza viruses by real-time PCR.ResultsOf the 1919 patient samples tested, 11 (0.6%) were co-infected with both influenza A(H1N1)pdm 2009 and influenza B/Victoria viruses. Similar observation was noted in four hospitalized patients during the same period. Patients at ages 1-72 years, and their clinical symptoms were similar to that of patients infected with either influenza A or B viruses. Of all patients, only one hospitalized patient was immunocompromised.In conclusion: Co-infection of influenza A(H1N1)pdm 2009 and influenza B viruses is an increasingly recognized phenomenon. This co-infection can occur not only in immunocompromised individuals, but also in immunocompetent patients. Although co-infection appears to be a rare event, it may still play a role in the epidemiology, pathogenicity and evolution of influenza viruses.