Critical influenza virus infection

Objective: To determine the risk of death from influenza infection in children with chronic underlying disease. Methodology: An 18-year retrospective study of children with 'critical' influenza A or B virus infection, defined as requiring admission to intensive care or resulting in death, but excluding laryngotracheobronchitis (LTB). Influenza infection was diagnosed by viral culture and/or immunofluorescence of respiratory secretions. Patients with LTB were analysed separately. Results: There were 27 cases of critical influenza virus infection over the study period, comprising 26 admissions to the intensive care unit (excluding LTB) and one death on the general wards. Thirteen (48%) of the 27 children had chronic underlying disease. In addition, 12 children with LTB were admitted to the intensive care unit. The LTB children were older and less likely to have chronic underlying disease. Nosocomial infection caused seven (26%) of the 27 critical infections. Nine (33%) of the 27 children with critical influenza died. Six (46%) of 13 children with chronic underlying disease and influenza admitted to intensive care died, compared with three of 14 (21%) without any underlying disease (odds ratio = 3.1, 95% confidence interval 0.6-14.0). Conclusions: Critical life-threatening influenza virus infection was uncommon, but the mortality was high (33%), particularly in children with chronic underlying disease. Nosocomial infection with influenza was an important cause of admission to intensive care.