Nested case-control study on the risk factors of colorectal cancer

Table 1 The distribution of subjects by age and sex

age	male		female
	case	control	case	control
30-	3	15	7	35
35-	9	49	3	15
40-	14	69	3	19
45-	11	52	14	66
50-	21	110	14	78
55-	24	114	22	104
60-	11	57	13	63
65-	11	54	3	15
70-	2	10	5	26
75-	2	10	3	14
80-	0	0	1	5
Total	108	540	88	440

Table 2 Results of univariate analysis for colon cancer (cases n = 84, controls n = 420)

factors	OR	95%CI	χ2	P
pork eating(y = 1, n = 0)	1.481		0.846	2.593	1.890	0.169
drining mixed water source* (y = 1, n = 0)	2.273	1.255	4.117	7.332	0.007
drining gutter water (y = 1, n = 0)	1.639	0.777	3.457	1.680	0.195
drining well water (y = 1, n = 0)	0.542	0.338	0.870	6.445	0.011
chronic diarrhea history(y = 1, n = 0)	2.018	1.003	4.060	3.871	0.049
constipaton history(y = 1, n = 0)	0.483	0.171	1.363	1.888	0.169
appendicitis history(y = 1, n = 0)	1.697	0.966	2.981	3.386	0.066
appendix operating history(y = 1, n = 0)	1.707	0.873	3.334	2.446	0.118
intestinal polyps history(y = 1, n = 0)	6.503	2.009	21.049	9.762	0.002

*drinking mixed water source refers to the subjects drinking different type of water sources through his/her lifetime, mostly drinking river water and gutter water. So is Table 2, Table 3 and Table 4

Table 3 Results of univariate analysis for rectal cancer (cases n = 112, controls n = 560)

factors	OR	95%CI	χ2	P
drining mixed water source (y = 1, n = 0)	2.021		1.170	3.491	6.363	0.011
mucious blood history (y = 1, n = 0)	2.138	1.122	4.072	5.335	0.021
defaecation drug using (y = 1, n = 0)	2.280	0.711	7.312	1.923	0.166
cholecyst excision history (y = 1, n = 0)	2.294	0.715	7.352	1.195	0.163

In Table 2, it was showed that four variables, well water drinking, mixed water source drinking, chronic diarrhea history and intestinal polyp history, were significantly associated with colon cancer (P < 0.05). The factor of appendicitis history showed an OR value close to significant level (P = 0.066). For rectal cancer in Table 3, there were two variables reached the significant level of P = 0.05, which were mixed water source drinking (OR = 2.02) and mucous blood stool history (OR = 2.14).

Table 4 Results of multivariate analysis for colon cancer

factors	OR	95%CI	P
drining mixed source water (y = 1, n = 0)	2.387		1.243	4.587	0.009
mucous blood history (y = 1, n = 0)	3.508	1.370	8.985	0.009

Table 4 and Table 5 illustrated that, at P = 0.05 level, both for colon cancer and rectal cancer, the final logistic regression model comprised two factors: mixed water source drinking and mucous blood stool history.

Table 5 Results of multivariate analysis for rectal cancer

factors	OR	95%CI	P
drinking mixed water source (y = 1, n = 0)	1.951		1.086	3.506	0.025
mucous blood history (y = 1, n = 0)	2.139	1.040	4.402	0.039
factors	2.870	1.117	7.371	0.029