Spatial cluster mapping and environmental modeling in pediatric inflammatory bowel disease

Table 1 British Columbia average pediatric incidence for inflammatory bowel disease, Crohn’s disease, ulcerative colitis, and inflammatory bowel disease-unclassified from 2001–2016

Diagnosis	Health authority	Cases	Incidence per 100000	95%CI for incidence
All IBD	All British Columbia	1183	9.22	8.7	9.76
	Fraser	558	10.95	10.06	11.9
	Interior	143	7.15	6.03	8.43
	Northern	64	6.17	4.75	7.88
	Vancouver Coastal	254	9.28	8.17	10.49
	Vancouver Island	164	8.36	7.13	9.74
CD	All British Columbia	780	6.08	5.66	6.52
	Fraser	356	6.99	6.28	7.74
	Interior	96	4.8	3.89	5.85
	Northern	40	3.86	2.76	5.24
	Vancouver Coastal	166	6.06	5.18	7.06
	Vancouver Island	122	6.22	5.17	7.43
UC	All British Columbia	288	2.24	1.99	2.52
	Fraser	151	2.96	2.51	3.48
	Interior	32	1.6	1.09	2.26
	Northern	16	1.54	0.88	2.51
	Vancouver Coastal	62	2.27	1.74	2.9
	Vancouver Island	27	1.38	0.91	2
IBD-U	All British Columbia	115	0.9	0.74	1.08
	Fraser	51	1	0.75	1.32
	Interior	15	0.75	0.42	1.24
	Northern	8	0.77	0.33	1.52
	Vancouver Coastal	26	0.95	0.62	1.39
	Vancouver Island	15	0.76	0.43	1.26

IBD: Inflammatory bowel disease; CD: Crohn’s disease, UC: Ulcerative colitis; IBD-U: Inflammatory bowel disease-unclassified.

Table 2 Data used in environmental exposure modeling

Variable	Description	Data source and database
Income	Mean of 2005 (adjusted to 2015 dollars) and 2015 census average family income for Local Health Areas	Statistics Canada, BC Community Health Atlas
Ethnicity	Census percent of the population of South Asian, Indigenous, Chinese, Jewish, and Non-Jewish European ethnic origin	Statistics Canada, University of Toronto Computing in the Humanities and Social Sciences Data Centre
Family size	Census average family size	Statistics Canada, University of Toronto Computing in the Humanities and Social Sciences Data Centre
Rurality	Percent of residents in each Local Health Area who lived outside a census metropolitan area or census agglomeration	Statistics Canada
NDVI greenness	Green vegetation cover calculated from land satellite imagery of surface reflection. Maximum and average growing season (May – August) NDVI within 250 m from postal code location. Multiplied by 100 so changes could be assessed as percentages	United States Geological Survey, Canadian Urban Environmental Health Research Consortium
UV vitamin D	Long-term stable monthly mean daily vitamin D dose from solar UV radiation adjusted for postal code elevation (J/m-2) which was averaged for winter (December through February) and summer (June through August)	Environment Canada and Cancer Care Ontario, Canadian Urban Environmental Health Research Consortium
NO2 air pollution	Annual average NO2 concentration in parts per billion	Canadian Urban Environmental Health Research Consortium
O3 air pollution	Average of O3 taken from the highest rolling 8-hour daily average concentration (parts per billion)	Environment and Climate Change Canada, Canadian Urban Environmental Health Research Consortium
PM2.5 air pollution	Annual average surface PM2.5 (μg/m3) concentration	Atmospheric Composition Analysis Group, Canadian Urban Environmental Health Research Consortium
Metam pesticide	2015 metam pesticide applied to fruits and vegetables (kg/ha/yr)	Global Pesticide Grids, Version 1.01, based on the United States Geological Survey’s Pesticide National Synthesis Project and the Food and Agriculture Organization Corporate Statistical Database pesticide databases
Petroleum oil pesticide	2015 petroleum oil employed for grapes and orchards (kg/ha/yr)	Global Pesticide Grids, Version 1.01, based on the United States Geological Survey’s Pesticide National Synthesis Project and the Food and Agriculture Organization Corporate Statistical Database pesticide databases
Glyphosate pesticide	2015 total glyphosate employed in major crops (wheat, corn, alfalfa, and others) in (kg/ha/yr)	Global Pesticide Grids, Version 1.01, based on the United States Geological Survey’s Pesticide National Synthesis Project and the Food and Agriculture Organization Corporate Statistical Database pesticide databases
Population age 0-16.9	Yearly estimates of population age 0-16.9 for Local Health Areas averaged for 2001–2016	Statistics Canada, BC Stats

BC: British Columbia; NDVI: Normalized difference vegetation index; NO₂: Nitrogen dioxide; O₃: Ozone; PM_2.5: Fine particulate matter; UV: Ultraviolet.

Table 3 Summary statistics for variables of interest for the 88 local health areas used for modeling

Explanatory variable	Minimum LHA value	Maximum LHA value	Mean of LHA values
Chinese ethnic origin (%)	0.00	47.21	4.35
Indigenous ethnic origin (%)	1.07	93.22	14.38
Jewish ethnic origin (%)	0.00	2.82	0.45
Non-Jewish European ethnic origin (%)	10.67	90.98	70.91
South Asian ethnic origin (%)	0.00	31.19	2.71
Average family income ($)	60265.01	216769.60	91884.26
Family size	2.25	3.13	2.76
Population density (per square km)	0.01	9443.44	553.95
Rural population (%)	0.00	100.00	53.05
NDVI maximum	0.59	0.80	0.70
NDVI mean	0.23	0.62	0.45
NO2 (ppb)	0.10	23.61	7.71
O3 (ppb)	17.49	39.54	30.14
PM2.5 (μg m3)	2.73	8.32	6.02
UV vitamin D summer (J/m-2)	4488.80	7272.52	6053.15
UV vitamin D winter (J/m-2)	102.02	449.6	274.98
Glyphosate used in common crops (kg/ha/yr)	0.00	6.71	0.61
Glyphosate used in alfalfa crops (kg/ha/yr)	0.00	0.17	0.02
Glyphosate used in corn crops (kg/ha/yr)	0.00	6.06	0.49
Glyphosate used in wheat crops (kg/ha/yr)	0.00	0.21	0.02
Metam used in fruits and vegetables (kg/ha/yr)	0.00	8.82	0.60
Petroleum oil used in orchards and grapes (kg/ha/yr)	0.00	4.75	0.28

LHA: Local Health Area; NDVI: Normalized difference vegetation index; UV: Ultraviolet; NO₂: Nitrogen dioxide; O₃: Ozone; PM_2.5: Fine particulate matter.

Table 4 Incidence rate ratios and 95%CIs for the best model explaining inflammatory bowel disease, Crohn’s disease, and ulcerative colitis rates in local health areas of British Columbia, Canada (n = 88)

Variable	Inflammatory bowel disease		Crohn’s disease		Ulcerative colitis
	IRR and 95%CI	P value	IRR and 95%CI	P value	IRR and 95%CI	P value
Average family size	0.467 (0.268–0.816)	0.007b
Average family income			0.912 (0.827–1.006)	0.064
Glyphosate used in alfalfa crops					0.001 (0.000–0.253)	0.024a
Glyphosate used in corn crops					0.828 (0.707–0.974)	0.021a
Glyphosate used in wheat crops					121.196 (2.252–6671.461)	0.019a
Indigenous ethnic origin	0.956 (0.941–0.971)	< 0.001c	0.923 (0.895–0.951)	< 0.001c
Metam used in fruits and vegetables	0.931 (0.892–0.970)	0.001b
NDVI Maximum at 250 m (× 100)	1.060 (1.040–1.082)	< 0.001c	1.038 (1.014–1.062)	0.002b
NDVI Mean at 250 m (× 100)					1.043 (1.013–1.075)	0.006b
NO2			0.952 (0.919–0.986)	0.006b
O3			0.947 (0.909–0.987)	0.010a	1.095 (1.039–1.154)	0.001b
Petroleum oil used in orchards and grapes	1.135 (1.007–1.270)	0.033a	1.159 (1.002–1.326)	0.038a
PM2.5	1.294 (1.113–1.507)	0.001b	1.230 (1.056–1.435)	0.008b
Rural population					0.990 (0.983–0.996)	0.004b
South Asian ethnic origin	1.020 (1.011–1.028)	< 0.001c			1.054 (1.030–1.079)	< 0.001c
UV Summer	0.9993 (0.9990–0.9996)	< 0.001c	0.9997 (0.9993–1.0001)	0.091
UV Winter					0.996 (0.992–1.000)	0.067

^aP < 0.05.

^bP < 0.01.

^cP < 0.001.

IRR: Incidence rate ratio; NDVI: Normalized difference vegetation index; NO₂: Nitrogen dioxide; O₃: Ozone; PM_2.5: Fine particulate matter; UV: Ultraviolet.