Interactions between CagA and smoking in gastric cancer

Table 4 Risk and synergy index¹ of non-cardia gastric cancer according to CagA positive Helicobacter pylori infection and smoking n (%)

	Cases(n = 257)	Control(n = 514)	Crude		Adjusted2		SF	SF (95% CI)	Z	P
			OR	95% CI	OR	95% CI
Smoking status							2.257	1.133-4.496	2.315	0.021a
CagA (-) and never smoked	30 (11.7)	269 (52.4)	1.0		1.0
CagA (-) and smoking	45 (17.5)	105 (20.4)	3.5	1.9-5.1	2.7	1.3-4.9
CagA (+) and never smoked	60 (23.3)	85 (16.5)	3.5	1.8-5.3	3.2	1.5-6.8
CagA (+) and smoking	122 (47.5)	55 (10.7)	8.7	5.1-11.9	19.5	10.3-42.2

^aP < 0.05. ¹Synergy index, is the ratio of the observed odds ratio (OR) for both factors combined, to the predicted OR assuming independent effects of each factor;

²Adjusted for education, alcohol consumption and family history of gastric cancer.