Journal of medical virology
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The novel pandemic (pdm) influenza A (H1N1) 2009 virus caused an epidemic of critical illness, with some patients developing severe acute respiratory distress syndrome. Pdm H1N1 2009 infection has been reported to cause fatal encephalopathy and myocarditis as well as pneumonia. To investigate the actual characteristics of the encephalopathy associated with pdm H1N1 2009 infection in Japan, questionnaires were distributed and information collected on 207 cases of encephalopathy during one season. ⋯ Among the 149 cases with good outcomes, 29 of 116 cases (25%) showed abnormalities on MRI, and 14 of these demonstrated reversible splenial lesions. Abnormal behaviors, especially delirium and visual hallucinations, were observed more frequently in cases without sequelae. In conclusion, pdm H1N1 2009 infection-associated encephalopathy was a critical disease in children, with rapidly progressive characteristics similar to those of seasonal influenza-associated encephalopathy.