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2005 Abstracts
98
INFLUENZA AND ACUTE CHILDHOOD ENCEPHALITIS
R Amin, A Bitnun, S Richardson, D Macgregor, R Tellier, H Heurter, L Ford-Jones
The Hospital for Sick Children, Toronto, Ontario
All children admitted and diagnosed with acute childhood encephalitis at The Hospital for Sick Children, Toronto, between January 1994 and November 2004 underwent extensive neurological and microbiological investigations. All children so diagnosed were enrolled in a consecutive cohort registry study. Acute and convalescent influenza A and B serology were tested in parallel using the complement fixation test (CF). Seropositivity was defined as a four-fold rise in titer. Nasopharyngeal swabs were examined for the presence of influenza A and B by direct immunofluorescence (DFA) and viral culture. All children in whom influenza A or B was detected in the nasopharynx and/or had positive serology were included in this report.
A total of 272 children with acute childhood encephalitis were evaluated; evidence of influenza A or B infection was detected in 22. The mean age was 4.3 years. Influenza A or B infection was demonstrated by detection of the virus in nasopharyngeal swabs alone in 15 patients, by serology alone in 3 patients and by both in 4 patients. Influenza B infection occurred in 3 patients. Fever was present in all patients. Prodromal respiratory symptoms occurred in 86% of patients. The interval between respiratory symptoms and neurologic manifestations varied from 1 to 14 days with a mean of 6 days and a median of 3 days. Seven of the 22 patients had evidence of acute coinfection; Mycoplasma pneumoniae in 5, herpes simplex virus in 1 and both herpes simplex virus and human herpes virus 6 in 1. Fifty percent of patients had abnormal CSF findings. EEG and neuroimaging abnormalities were demonstrated in 81% and 41% of patients, respectively. Two patients developed acute disseminated encephalomyelitis. Four patients were treated with antivirals. Neurologic sequelae occurred in 57% of patients.
In this prospective registry, influenza A and B were associated with 8% (22/272) of acute childhood encephalitis cases. The pathogenesis of infection by direct invasion of the central nervous system versus a cytokine/immunologic mechanism may explain the clustering of children into two groups: prodrome of £5 days or >6 days. Normal neuroimaging was associated with better outcomes. Coinfection with M pneumoniae and herpes group viruses was common. Influenza-associated encephalitis has significant morbidity and the efficacy of the influenza vaccine in CNS protection is an area of future study.