Table 3.

Attack rates (AR) and relative risk of acute gastroenteritis associated with specific risk factors stratified by age (years), pooled data from four lakes

Exposure	Exposed			Unexposed			Risk ratio	95% CI	P
	Total	Cases	AR%	Total	Cases	AR%
Lake A	342	78	22.81	1111	166	14.94	1.53	1.20–1.94	0.001
Lake B	163	54	33.13	1290	190	14.73	2.25	1.74–2.90	0.000
Lake C	211	27	12.80	1242	217	17.47	0.73	0.50–1.06	0.093
Lake D	289	46	15.92	1164	198	17.01	0.94	0.70–1.26	0.656
Swallowing water while swimming	209	65	31.10	1016	111	10.93	2.85	2.18–3.72	0.000
0–4	51	14	27.45	11	1	9.09	3.02	0.44–20.62	0.197
5–17	110	44	40.00	103	31	30.10	1.33	0.92–1.93	0.130
⩾18	46	7	15.22	890	78	8.76	1.74	0.85–3.55	0.137
Submersing head under water	943	206	21.85	474	32	6.75	3.24	2.27–4.62	0.000
0–4	52	21	40.38	44	5	11.36	3.55	1.46–8.64	0.001
5–17	271	112	41.33	23	3	13.04	3.17	1.09–9.19	0.008
⩾18	604	71	11.75	402	24	5.97	1.97	1.26–3.07	0.002
Getting water in the mouth while swimming	720	166	23.06	519	36	6.94	3.32	2.36–4.68	0.000
0–4	78	23	29.49	8	1	12.50	2.36	0.37–15.23	0.308
5–17	239	103	43.10	25	4	16.00	2.69	1.08–6.69	0.009
⩾18	387	39	10.08	483	31	6.42	1.57	1.00–2.47	0.049
Playing on the wet sand	394	98	24.87	1002	131	13.07	1.90	1.50–2.41	0.000
0–4	87	24	27.59	11	2	18.18	1.52	0.41–5.56	0.506
5–17	149	59	39.60	138	53	38.41	1.03	0.77–1.38	0.836
⩾18	150	15	10.00	837	74	8.84	1.13	0.67–1.92	0.648
Eating own food	670	116	17.31	743	110	14.80	1.17	0.92–1.49	0.199
0–4	70	17	24.29	28	7	25.00	0.97	0.45–2.08	0.941
5–17	163	66	40.49	127	45	35.43	1.14	0.85–1.54	0.379
⩾18	425	32	7.53	579	57	9.84	0.76	0.51–1.16	0.202

Waterborne outbreak, Tampere, 2014.