[Estimating the burden of influenza-associated hospitalization for cases of severe acute respiratory infection, Beijing, 2015]

Objective: To estimate the influenza infection rate among severe acute respiratory infection(SARI) cases and the hospitalization rates of SARI attributable to influenza, based on two sentinel hospital surveillance databases in Beijing, 2015. Methods: Surveillance was conducted at two sentinel hospitals in Beijing in 2015. A total of 1 842 patients who admitted to the sentinel hospitals and met the definition of SARI were enrolled in the study. The respiratory tract specimens of SARI cases were collected, and sent to laboratories within 48 hours for influenza RNA detection. The catchment area of sentinel hospitals was defined by reviewing the home address of inpatients; A total of 1 491 patients were sampled and tested for influenza. The population size of catchment areas was obtained from demographic year book. We investigated the number of pneumonia patients admitted to the sentinel hospitals and other hospitals in catchment areas in 2015, and calculated the proportions of pneumonia patients that were admitted to sentinel hospitals in catchment areas. The catchment population size was calculated using the number of total population of catchment areas multiply by the proportions of pneumonia patients that were admitted at sentinel hospitals. Results: Among 1 491 patients, 13.7% (205 cases) was test positive for influenza viruses, 2 (0.9%) cases positive for influenza A (H1N1), 91 (44.6%) cases influenza A (H3N2), 1 (0.5%) case influenza B/Victoria, 111 (54.0%) cases influenza B/Yamagata. Influenza was associated with an estimated 30 (95%CI:9-51) SARI hospitalizations per 100 000 during 2015. The hospitalization rate was 243 (95%CI: 232-255), 86 (95%CI: 59-112),1(95%CI: 0-5), 8 (95%CI: 0-23) and 92 (95%CI: 16-168) SARI hospitalizations per 100 000 population for<5 years children, 5-14 years children, 15-24 years adult, 25-59 years adult and ≥60 years population, respectively. The hospitalization rate of SARI attributed to influenza A and B was 14 (95%CI:4-17) and 16 (95%CI:0-23) per 100 000 population, respectively. Conclusion: The influenza positive rate among SARI cases was relatively high. The hospitalization burden of SARI attributed to influenza was the greatest in children under 5 year-old.