[Severe "malignant" influenza in the light of past history]

The first influenza pandemic of the xxist century is due to a novel A (H1N1) strain. The infection, which affects younger patients than seasonal influenza, presents most often under a benign form. But it can rarely and rapidly evolve to pulmonary parenchymal involvement, independently of any bacterial superinfection or co-infection. It becomes a true viral pneumonia, which can evolve to acute respiratory distress syndrome (ARDS). This phenomenon was well described for the three xxth century pandemics, especially for the 1968-1969 one. These cases of "malignant flu" benefitted from the great breakthroughs in medical intensive care made in the previous 15 years. The specificity of these pandemic strains to infect lower respiratory tract is of immunological origin: only patients with little or no immunity to the virus can develop viral pneumonia and ARDS. This is why trivalent vaccination against seasonal flu appears to be somewhat protective against severe presentations of the disease. During winter 2009-2010, an inflow of flu-related ARDS cases is expected in French ICUs. Aggressive oxygenation techniques, high dose and prolonged antiviral treatment, and steroid adjunctive therapy, could be used, adding to the experience acquired during previous pandemics.