An outbreak of Japanese encephalitis in a non-endemic region of north-east India

Background There are few comprehensive reports of epidemic Japanese encephalitis in a previously unaffected region. We report our experience of a first-ever outbreak of it in Sonitpur District, Assam, India, with 45 laboratory-confirmed cases at a single hospital.

Method Between 2 July and 11 August 2008, patients meeting the WHO definition of acute encephalitis syndrome were assessed in a single hospital and had tests including blood and cerebrospinal fluid for Japanese encephalitis antibody titres.

Results Ninety-six cases meeting the definition of acute encephalitis syndrome were identified with 45 cases of Japanese encephalitis confirmed by cerebrospinal fluid or blood results. For Japanese encephalitis positive patients, mean age was 36 (range 4–80). Of the 45, 11 (24%) died and a further 21 (47%) had significant residual deficits. Focal neurological signs (40%) and seizures (25%) were common.

Conclusion An effective Japanese encephalitis vaccine is the key intervention for limiting the population impact of this disease. Identification of these cases led to a district-wide mass vaccination campaign.