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A spatial and temporal analysis of notifiable gastrointestinal illness in the Northwest Territories, Canada, 1991-2008

Aliya Pardhan-Ali1*, Olaf Berke12, Jeff Wilson3, Victoria L Edge1, Chris Furgal4, Richard Reid-Smith1, Maria Santos5 and Scott A McEwen1

Author Affiliations

1 Department of Population Medicine, University of Guelph, Guelph, ON, Canada

2 Department of Mathematics and Statistics, University of Guelph, Guelph, ON, Canada

3 Novometrix Research Inc, Moffat, ON, Canada

4 Department of Indigenous Environmental Studies, Trent University, Peterborough, ON, Canada

5 Department of Health and Social Services, Government of the Northwest Territories, Yellowknife, NT, Canada

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International Journal of Health Geographics 2012, 11:17  doi:10.1186/1476-072X-11-17

Published: 29 May 2012

Abstract

Background

This is the first study to describe the geographical and temporal distribution of notifiable gastrointestinal illness (NGI) in the Northwest Territories (NWT), Canada. Understanding the distribution of NGI in space and time is important for identifying communities at high risk. Using data derived from the Northwest Territories Communicable Disease Registry (NWT CDR), a number of spatial and temporal techniques were used to explore and analyze NGI incidence from the years 1991 to 2008. Relative risk mapping was used to investigate the variation of disease risk. Scan test statistics were applied to conduct cluster identification in space, time and space-time. Seasonal decomposition of the time series was used to assess seasonal variation and trends in the data.

Results

There was geographic variability in the rates of NGI with higher notifications in the south compared to the north. Incidence of NGI exhibited seasonality with peaks in the fall months for most years. Two possible outbreaks were detected in the fall of 1995 and 2001, of which one coincided with a previously recognized outbreak. Overall, incidence of NGI fluctuated from 1991 to 2001 followed by a tendency for rates to decrease from 2002 to 2008.

Conclusions

The distribution of NGI notifications varied widely according to geographic region, season and year. While the analyses highlighted a possible bias in the surveillance data, this information is beneficial for generating hypotheses about risk factors for infection.

Keywords:
Gastrointestinal illness; Foodborne diseases; Waterborne diseases; Minority health; Population surveillance; Spatial epidemiology; Temporal epidemiology; Spatio-temporal epidemiology