Epidemiology and aetiology of encephalitis in Canada, 1994–2008: a case for undiagnosed arboviral agents?

Abstract

Encephalitis is a clinical syndrome often associated with infectious agents. This study describes the epidemiology and disease burden associated with encephalitis in Canada and explores possible associations with arboviral causes. Encephalitis-associated hospitalizations, 1994-2008, were analysed according to aetiological category (based on ICD-9/ICD-10 codes) and other factors using multivariate logistic regression for grouped (blocked) data and negative binomial regression. A discrete Poisson model tested spatio-temporal clustering of hospitalizations associated with unclassified and arboviral encephalitis aetiologies. Encephalitis accounted for an estimated 24028 hospitalizations in Canada (5·2/100 000 population) and unknown aetiologies represented 50% of these hospitalizations. In 2003, clusters of unclassified encephalitis were identified in the summer and early autumn months signifying potential underlying arboviral aetiologies. Spatio-temporal patterns in encephalitis hospitalizations may help us to better understand the disease burden associated with arboviruses and other zoonotic pathogens in Canada and to develop appropriate surveillance systems.

Encephalitis Hospitalization Rates and Inpatient Mortality in the United States, 2000-2010

“…As in previous studies, we found the highest rates of hospitalization for all-cause and herpes encephalitis at extremes of age [4], [23], [25]. Rates of West Nile Virus encephalitis-associated hospitalizations were lowest in those 19 years of age and under, higher in the 45–64 age group, and highest in those 65 and over, paralleling West Nile Virus national surveillance data collected through the passive surveillance system ArboNET by the Centers for Disease Control and Prevention from 1999–2008 [7].…”

“…Thus, both regional and seasonality data suggest that a substantial proportion of viral NOS cases may in fact be due to unrecognized arboviruses. These results parallel a recent study in Canada in which seasonal clusters of encephalitis were identified, suggesting that unidentified arboviral agents may underlie undetermined etiologies of encephalitis [25]. Taken together, these findings highlight the need for increased surveillance and improved diagnostic modalities to identify arboviral encephalitis.…”

“…Of note, a trend for increased encephalitis-associated hospitalizations in women was also recently reported in Canada. This increase was attributed largely to an increased incidence of VZV encephalitis among women [25], which was not observed in our study. Thus, our findings of a change in gender-specific hospitalization rates associated with encephalitis may reflect, in part, increased awareness, diagnosis and coding of autoimmune encephalitides.…”

“…The overall rate of hospitalization, 7.3 per 100,000 population, was not different from that reported in the U.S. over ten years earlier [4], nor did the rate differ from that reported by Vora et al (2014) [6]; however, it was higher than reported rates from hospital discharge data in France, Italy, Canada, and Australia [22]–[25]. Modest reductions were observed in the mean length of stay and in-hospital mortality compared to findings from the previous decade [4].…”

“…Viral causes continue to account for the majority of cases in which an etiology is identified, although a substantial proportion of cases are now associated with Other Specified (predominantly autoimmune) causes. As has been the case in numerous studies spanning the last several decades, approximately 50% of cases had a specific etiology assigned [1], [2], [4], [23]–[25], [29].…”