Background
Methods
Search strategy
Selection criteria
Data extraction
Statistical analysis
Results
Literature search
Demographic and study quality characteristics
Study characteristics and demographics | Study Quality Characteristics | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
Author (year) | Country | Study period | Number of cases | Incidence of UC (per 100,000) | Methods of diagnosis defined | Diagnosis based on recognized criteria | Urban/rural defined | Urban population >10,000 | Time of exposure | Multiple levels of exposure |
Ulcerative Colitis
| ||||||||||
Mate-Jimerez 1994[39] | Spain | 1981-88 | 111 | 3.16 | Yes | Yes | Yes | Yes | At diagnosis | No |
Ekbom 1991[40] | Sweden | 1965-83 | 2509 | 10.5 | Yes | Yes | Yes | No | At diagnosis | No |
Linden 1971[19] | Finland | 1967 | 223 | 4.76 | No | N/A | No | No | At diagnosis | No |
Probert 1992[32] | UK | 1972-80 | 192 | 5.33 | Yes | Yes | Yes | No | At diagnosis | Yes |
Probert 1992[32] | UK | 1981-89 | 211 | 7.29 | Yes | Yes | Yes | No | At diagnosis | Yes |
Niv 1990[33] | Israel | 1967-86 | 43 | 2.33 | Yes | No | Yes | No | At diagnosis | Yes |
Kildebo 1990[22] | Norway | 1983-86 | 179 | 13.2 | Yes | Yes | No | No | At diagnosis | No |
Gheorghe 2004[23] | Romania | 2002-03 | 163 | 0.97 | Yes | Yes | No | No | At diagnosis | No |
Sincic 2006[41] | Croatia | 2000-04 | 70 | 4.6 | Yes | Yes | Yes | No | At diagnosis | No |
Tsianos 1994[24] | Greece | 1982-91 | 61 | 4.18 | Yes | Yes | No | No | At diagnosis | Yes |
Ladas 2005[34] | Greece | 1990-94 | 56 | 10.6 | Yes | Yes | Yes | Yes | At diagnosis | Yes |
Moller 1971[20] | Finland | 1956-67 | 505 | 1.07 | Yes | Yes | No | No | At diagnosis | No |
Blanchard 2001[42] | Canada | 1987-96 | 1763 | 15.6 | Yes | Yes | Yes | No | At diagnosis | No |
Green 2006[15] | Canada | 1990-01 | N/A | 13.5 | No | N/A | Yes | No | At diagnosis | No |
Lakatos 2003[43] | Hungary | 1977-01 | 560 | 5.89 | Yes | Yes | Yes | No | At diagnosis | No |
Manousos 1996[44] | Greece | 1990-94 | 117 | 8.9 | Yes | Yes | Yes | No | At diagnosis | No |
Wigley 1962[35] | New Zealand | N/A | 132 | N/A | Yes | No | Yes | Yes | At diagnosis | Yes |
Latour 1996[45] | Belgium | 1993-94 | 36 | 3.5 | Yes | Yes | Yes | No | At diagnosis | No |
Crohn’s Disease
| ||||||||||
Kyle 1971[47] | UK | 1955-69 | 166 | 1.98 | Yes | Yes | Yes | No | At diagnosis | No |
Jayanthi 1992[48] | UK | 1972-80 | 161 | 2.89 | Yes | Yes | Yes | Yes | At diagnosis | No |
Jayanthi 1992[48] | UK | 1981-89 | 233 | 4.48 | Yes | Yes | Yes | Yes | At diagnosis | No |
Mate-Jimerez 1994[39] | Spain | 1981-88 | 57 | 1.61 | Yes | Yes | Yes | Yes | At diagnosis | No |
Ekbom 1991[40] | Sweden | 1965-83 | 1469 | 6.09 | Yes | Yes | Yes | No | At diagnosis | No |
Shivananda 1987[36] | Netherlands | 1979-83 | 54 | 3.90 | Yes | Yes | Yes | No | At diagnosis | Yes |
Kildebo 1989[22] | Norway | 1983-86 | 82 | 5.85 | Yes | Yes | No | No | At diagnosis | No |
Kyle 1992[49] | Scotland | 1955-88 | 856 | 5.65 | Yes | Yes | Yes | No | At diagnosis | No |
Manousos 1996[44] | Greece | 1990-94 | 37 | 3.00 | Yes | Yes | Yes | Yes | At diagnosis | No |
Gheorghe 2004[23] | Romania | 2002-03 | 85 | 0.51 | Yes | Yes | No | No | At diagnosis | No |
Sincic 2006[41] | Croatia | 2000-04 | 100 | 6.50 | Yes | Yes | Yes | No | At diagnosis | No |
Phavichitr 2003[25] | Australia | 1971-01 | 351 | 1.02 | Yes | Yes | No | No | At diagnosis | No |
Moum 1996[50] | Norway | 1990-93 | 225 | 5.86 | Yes | Yes | Yes | No | At diagnosis | No |
Blanchard 2001[42] | Canada | 1987-96 | 1765 | 15.6 | Yes | Yes | Yes | No | At diagnosis | No |
Green 2006[15] | Canada | 1990-01 | N/A | 14.8 | No | N/A | Yes | No | At diagnosis | No |
Lakatos 2003[43] | Hungary | 1977-01 | 212 | 2.23 | Yes | Yes | Yes | No | At diagnosis | No |
Nyhlin 1986[51] | Sweden | 1974-81 | 253 | 4.90 | Yes | Yes | Yes | No | At diagnosis | No |
Ruiz Ochoa 1984[30] | Spain | 1976-83 | 152 | 0.80 | Yes | Yes | No | No | At diagnosis | No |
Sedlack 1980[31] | USA | 1935-75 | 103 | 4.20 | Yes | No | No | No | At diagnosis | No |
Brandes 1983[52] | Germany | 1964-75 | 97 | 3.00 | Yes | No | Yes | No | At diagnosis | No |
Latour 1996[45] | Belgium | 1993-94 | 56 | 5.50 | Yes | Yes | Yes | No | At diagnosis | No |
Study characteristics and demographics | Study quality characteristics | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Author (year) | Country | No. of cases | No. of controls | Source of controls | Controls matched for: | Methods of diagnosis defined | Diagnosis based on recognized criteria | Urban/rural defined | Urban population >10,000 | Time of exposure | Multiple levels of exposure |
Ulcerative Colitis
| |||||||||||
Parrello 1997[26] | Italy | 509 | 657 | Attending orthopedic and surgical clinics | Sex, age, year of diagnosis | Yes | Yes | No | No | Time of data collection | No |
Feeney 2002[17] | UK | 137 | 137 | Functional GI Disorders | Sex, age | Yes | Yes | No | No | Childhood (age 0–5) | No |
Bernstein 2007[27] | Canada | 137 | 310 | Manitoba Health Population Registry | Sex, age | No | N/A | No | No | N/A | No |
Jiang 2007[28] | China | 177 | 177 | Neighbours or colleagues | Sex, age | Yes | Yes | No | No | Childhood | No |
Radon 2007[54] | Germany | 304 | 1481 | Strabismus surgery | Age | No | N/A | No | No | Time of data collection | No |
Martinez Salmeron 1994[46] | Spain | 63 | 63 | Hospital | Sex, age | Yes | Yes | Yes | No | Time of data collection | No |
Ekbom 1990[8] | Sweden | 164 | 328 | Live births between 1924–1957 in Uppsala County | Date of birth, sex, and maternal age or parity | Yes | Yes | Yes | No | Time of birth | No |
Crohn’s Disease
| |||||||||||
Feeney 2002[17] | UK | 139 | 139 | Functional GI disorders | Sex, age | Yes | Yes | No | No | Childhood (age 0–5) | No |
Bernstein 2007[27] | Canada | 235 | 310 | Manitoba Health Population Registry | Sex, age | No | N/A | No | No | N/A | No |
Ponsonby 2009[53] | Australia | 278 | 998321 | Live births from 1983–1998 in Victoria | Age | Yes | No | Yes | No | Childhood (age 0–6) | No |
Malekzadeh 2009[16] | Iran | 196 | 207 | IBS treated by an expert gastroenterologist | Age | Yes | Yes | No | No | Childhood (before 16th birthday) | No |
Radon 2007[54] | Germany | 444 | 1481 | Strabismus surgery | Age | No | N/A | No | No | Time of data collection | No |
Thompson 1998[29] | England, Wales | 291 | 1682 | Same GP | Sex, age | No | N/A | No | No | N/A | No |
Wurzelmann 1994[13] | United States | 322 | 262 | Closest neighbour | Sex, age, race | No | N/A | No | No | Childhood (age 0–5) | Yes |
Martinez Salmeron 1994[46] | Spain | 30 | 30 | Hospital | Sex, age | Yes | Yes | Yes | No | Time of data collection | No |
Ekbom 1990[8] | Sweden | 93 | 186 | Live births between 1924–1957 in Uppsala County | Date of birth, sex, and maternal age or parity | Yes | Yes | Yes | No | Time of birth | No |
Urban/rural environment and IBD
Sensitivity and stratified analyses
Ulcerative colitis | Crohn’s disease | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Stratified analysis | Meta-regression | Stratified analysis | Meta-regression | |||||||||
No. of studies | No. of cases | Pooled RR (95%CI) | Heterogeneity (p-value) | Coef. | P value | No. of studies | No. of cases | Pooled RR (95%CI) | Heterogeneity (p-value) | Coef. | P value | |
Crude | 18 | 6901 | 1.19(1.03, 1.36) | <.001 | 21 | 6514 | 1.50(1.30, 1.72) | <.001 | ||||
Definition of urban/rural environment
| ||||||||||||
Urban/rural defined | 13 | 5906 | 1.18(1.09, 1.27) | .19 | 16 | 5741 | 1.28(1.14, 1.43) | <.001 | ||||
Urban defined as >10,000 | 3 | 299 | 1.16(0.90, 1.50) | .65 | 4 | 488 | 1.38(0.97, 1.97) | .072 | ||||
Year of publication
| ||||||||||||
1962-1988 | 3 | 860 | 0.96(0.60, 1.51) | <.001 | 0.16 | .30 | 6 | 825 | 1.90(1.27, 2.85) | <.001 | −0.095 | .47 |
1989-1998 | 9 | 3459 | 1.23(0.95, 1.57) | <.001 | 9 | 3176 | 1.26(1.04, 1.53) | <.001 | ||||
1999-2009 | 6 | 2612 | 1.30(1.10, 1.54) | .022 | 6 | 2513 | 1.49(1.18, 1.87) | .001 | ||||
Region
| ||||||||||||
European countries | 15 | 5036 | 1.21(0.99, 1.46) | <.001 | 0.008 | .98 | 17 | 4295 | 1.55(1.28, 1.88) | <.001 | 0.77 | .75 |
Non-European countries | 3 | 1895 | 1.13(1.06, 1.22) | .61 | 4 | 2219 | 1.39(1.18 1.62) | .12 | ||||
European Countries
| ||||||||||||
Northern | 6 | 3819 | 0.97(0.75, 1.27) | <.001 | −0.26 | .086 | 9 | 3499 | 1.23(1.04, 1.45) | <.001 | 0.23 | .04 |
Eastern | 2 | 723 | 1.59(0.98, 2.59) | .013 | 2 | 297 | 2.30(0.54, 9.82) | <.001 | ||||
Mediterranean | 6 | 458 | 1.39(0.82, 2.36) | <.001 | 4 | 346 | 2.64(1.50, 4.62) | .02 | ||||
Western | 1 | 36 | 2.12(1.00, 4.50) | NA | 2 | 153 | 1.72(1.17, 2.51) | .79 |
Ulcerative colitis | Crohn’s disease | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Stratified analysis | Meta-regression | Stratified analysis | Meta-regression | |||||||||||
No. of studies | No. of cases | No. of controls | Pooled OR (95%CI) | Heterogeneity (p-value) | Coef. | P value | No. of studies | No. of cases | No. of controls | Pooled OR (95%CI) | Heterogeneity (p-value) | Coef. | P value | |
Crude | 7 | 1491 | 3153 | 1.06 (0.78, 1.45) | .004 | 9 | 2028 | 1002618 | 1.26 (1.03, 1.53) | .16 | ||||
Time of exposure
| ||||||||||||||
Time of data collection | 4 | 1013 | 2511 | 1.18 (0.78, 1.80) | .006 | -0.32 | .42 | 2 | 474 | 1511 | 1.21 (0.58, 2.50) | .18 | 0.060 | .89 |
Childhood | 3 | 478 | 642 | 0.87 (0.65, 1.17) | .91 | 5 | 1028 | 999115 | 1.18 (0.82, 1.70) | .052 | ||||
0-6 years | 4 | 832 | 998908 | 1.12 (0.71, 1.77) | .026 | 0.16 | .46 | |||||||
< 16 years | 1 | 196 | 207 | 1.39 (0.74, 2.60) | NA | |||||||||
Source of controls
| ||||||||||||||
Population | 2 | 314 | 487 | 1.02 (0.66, 1.58) | .16 | 0.035 | .94 | 3 | 835 | 998893 | 1.40 (1.13, 1.73) | .37 | -0.23 | .32 |
Clinic/Hospital | 5 | 1177 | 2666 | 1.06 (0.70, 1.60) | .003 | 6 | 1193 | 3725 | 1.09 (0.79, 1.51) | .11 |