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 2 Results of univariable negative binomial regression models (n = 846 cases from 153 FSAs)

Variable ^a)	Type		IRR ^c)(95% CI)	P - value
Average number of children at home per census family	Linear (X)		1.03 (0.71, 1.50)	0.881
	Quadratic (X^{^2}) ^b)		4.45 (1.81, 10.92)	0.001
Average number of persons per census family	Linear (X)		0.89 (0.64, 1.25)	0.515
	Quadratic (X^{^2})		4.47 (1.82, 10.98)	0.001
Average number of rooms per home	Linear (X)		0.97 (0.91, 1.04)	0.398
	Quadratic (X^{^2})		1.08 (1.03, 1.13)	0.002
Immigrant population proportion	Linear (X)		0.99 (0.99, 1.00)	0.284
	Quadratic (X^{^2})		0.99 (0.99, 0.99)	0.014
Average median family income	Categorical	Low (< CAD ^d) 65,000)	1.30 (1.08, 1.57)	0.005
		Medium (CAD 65,000 - 85,000)	Reference	-
		High (> CAD 85,000)	1.31 (1.08, 1.58)	0.006
Proportion of university graduates of persons between 25 to 64 years of age	Categorical	Low (10.4 - 28.6)	0.93 (0.77, 1.12)	0.446
		Medium (28.7 – 40.0)	Reference	-
		High (40.4 – 72.5)	0.95 (0.78, 1.16)	0.640
Unemployment rate of persons 15 years of age or older	Categorical	Low (0 - 6.0)	1.06 (0.87, 1.29)	0.544
		Medium (6.1 - 7.5)	Reference	-
		High (7.6 - 11.0)	1.08 (0.89, 1.32)	0.423
Visible minority population proportion	Categorical	Low (2.1 - 29.4)	0.78 (0.64, 0.94)	0.009
Visible minority population proportion	Categorical	Medium (29.5 - 51.8)	Reference	-
		High (51.9 - 93.4)	0.77 (0.64, 0.92)	0.004

^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