Relationship between different sources of drinking water, water quality improvement and gastric cancer mortality in Changle County - A retrospective-cohort study in high incidence area

Table 1 Gastric cancer mortality of Zhanggang Town according to the type of water supply (1/10⁵) (1973-1990)

Type of water source	Male	Female	Total
River Water	176.91	57.29	121.05
	(141/79699)1	(40/69822)	(181/149521)
Shallow well water	112.70	31.58	74.85
	(320/267979)	(74/234356)	(276/502335)
RR	1.57	1.81	1.62
χ2	19.88	9.49	28.79
P	< 0.01	< 0.01	< 0.01

¹Number of gastric cancer death cases/person-year observed.

Table 2 Types of the drinking water supply and gastric cancer mortality rates for seven towns, Zhanggang (1/10⁵)

Types of drinking		Male	Female	Total
water supply
River water (1)		122.83	46.10	86.03
		(107/87113)	(37/80263)	(144/167376)
Shallow well (2)		85.02	36.06	62.03
		(650/764555)	(244/676618)	(894/1441173)
Tap water (3)		51.31	3.86	29.78
		(16/31181)	(1/25906)	(17/57087)
RR		2.39	11.94	2.89
χ2	(1:3)	10.617	8.618	18.005
P		< 0.01	< 0.01	< 0.01
RR		1.66	9.34	2.08
χ2	(2:3)	3.673	6.524	8.872
P		> 0.01	> 0.05	> 0.01
RR		1.44	1.28	1.39
χ2	(1:2)	12.158	1.686	13.017
P		< 0.01	< 0.05	< 0.01

Table 3 Improved water and gastric cancer mortality rates for seven towns in Changle County (1/10⁵)

	Male			Female			Total
	Person-year observed	No. of deaths	Death rate	Person-year observed	No. of deaths	Death rate	Person-year observed	No. of deaths	Death rate
Persistent river water supply	37484	43	114.72	36856	12	32.56	74340	55	73.98
River water changed to tap water	35088	14	39.90	24262	4	16.49	59350	18	30.33
RR		0.35			0.51			0.41
χ2		12.93			1.44			11.52
P		0.0003b			0.2295			0.0007b
Persistent well water supply	411547	355	86.26	362687	118	35.23	774234	473	61.10
Well water changed to tap water	10449	3	28.71	8711	2	22.96	19160	5	26.10
RR		0.33			0.71			0.43
χ2		3.98			0.24			3.80
P		0.0460a			1.0000			0.0512a

^aP < 0.05,

^bP < 0.01.