Evaluating area-level spatial clustering of SalmonellaEnteritidis infections and their socioeconomic determinants in the greater Toronto area, Ontario, Canada (2007 – 2009): a retrospective population-based ecological study

Table 3 Results of the final multivariable negative binomial regression model (n = 846 cases from 153 FSAs)

Variable ^a)	Type		Estimate (95% CI)	IRR ^c)(95% CI)	P-value
Average number of children at home per census family	Linear (X) ^b)		0.22 (−0.20, 0.64)	1.24 (0.82, 1.89)	0.313
Average number of children at home per census family	Quadratic (X^{^2})		1.69 (0.84, 2.53)	5.40 (2.32, 12.54)	<0.001
Average median family income	Categorical	Low (< CAD ^d) 65,000)	0.29 (0.11, 0.47)	1.34 (1.12, 1.61)	0.002
		Medium (CAD 65,000 - 85,000)	Reference	-	-
		High (> CAD 85,000)	0.22 (0.03, 0.40)	1.24 (1.03, 1.49)	0.020
Visible minority population proportion	Categorical	Low (2.1 - 29.4)	−0.16 (−0.35, 0.036)	0.85 (0.70, 1.04)	0.110
		Medium (29.5 - 51.8)	Reference	-	-
		High (51.9 - 93.4)	−0.27 (−0.44, -0.10)	0.76 (0.64, 0.91)	0.002
Intercept	-	-	−0.12 (−0.29, 0.05)	-	0.178

^a) Dependent variable: Number of Salmonella Enteritidis infections by forward sortation area (FSA). Offset: natural log-transformed FSA-based expected number of cases. ^b) Each linear (continuous) variable was centered by substracting the mean value from each value. A quadratic term for the centered linear variable was introduced and kept in the model if it was significant. If the linear and quadratic terms were not statistically significant, the variable was categorized into three equal groups (low, medium, and high). ^c) IRR: incidence rate ratio; CI: confidence interval. ^d) CAD: Canadian Dollar. Significant at P ≤ 0.05.

ISSN: 1471-2458