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

Background Influenza A and B viruses co-infections are rare events and mainly occurred in immunocompromised patients. Objectives In 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 design Nasopharyngeal 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. Results Of 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.