Table 3.

The relative risk for AGI between the users using the water contaminated with E. coli and those using uncontaminated water for the three sizes of water supply zones.

The supply zone	E. coli positive samples	The no. of AGI patients	The no. of residents with no AGI notified	The relative risk (confidence interval)
≥ 10,000	yes	35	10 297	0.51 (0.37–0.71)
	no	7724	1 161 247
1000–10,000	yes	221	53 572	0.92 (0.80–1.06)
	no	1786	399 445
50–1000	yes	400	41 699	1.25 (1.12–1.40)
	no	1041	136 048