Validation of In-hospital Isolation Based on Viral Shedding of Seasonal Influenza

In-hospital isolation for patients with seasonal influenza is currently dependent on the facilities. In this study, we validated in-hospital isolation for patients who were diagnosed with seasonal influenza and admitted to our hospital from December 2018 to March 2020 using both viral copy numbers calculated by real-time RT-PCR method and viral culture. We collected each nasopharyngeal swab sample at the date of admission, and at three and seven days from admission, respectively, and determined viral copy numbers and cultivated viruses collected from each patient. Four patients were evaluated (73―90 years old; male: female, 3:1). The viral copy numbers decreased with time in three of the four patients (increased again at seven days from admission in the other patient). As for the viral culture, three of the four patients were positive both at the date of admission and three days from admission and negative at seven days from admission. The remaining patient was positive only at the date of admission. Thus, both viral shedding and infectiousness decrease with time in patients with seasonal influenza. The longest fever duration was six days in two patients, both of whom were complicated by pneumonia. On the basis of our findings, the longest indicated in-hospital isolation for inpatients with seasonal influenza is seven days after symptom onset or 24 hours after defervescence.