PCR on cerebrospinal fluid to show influenza-associated acute encephalopathy or encephalitis

Background Except for Reyeʹs syndrome, influenzaassociated acute encephalopathy or encephalitis is not universally recognised. We did a multicentre study of laboratory and clinical data for patients with influenza-associated acute encephalopathy or encephalitis. Methods In Nagoya, Japan, ten patients with acute encephalopathy or encephalitis associated with influenzalike illness were admitted to our hospitals between April, 1996, and March, 1997. We collected clinical, laboratory and serological data and assessed cerebrospinal fluid samples by PCR for influenza A and B. Findings Seven patients, aged 22 months to 4 years, had evidence of recent influenza infection, six with type-A/Hong Kong (H3N2) and one with type B. The first sign in the central nervous system appeared within 2 days of fever in all but one patient. The first sign of involvement of the central nervous system was generalised convulsions in all patients. Two patients died, one had sequelae, and four survived without sequelae. PCR for influenza type A was positive for five patients. Interpretation The results of PCR suggest that at least part of the influenza type A genome existed in the central nervous system. Influenza-associated acute encephalopathy or encephalitis in young children deserves wider recognition.