Baseline characteristics of included participants from the Walkerton Health Study and from the surrounding communities.
| Characteristics† | Residents of surrounding communities, no. (%)*n = 11 263 | Walkerton Health Study participants, no. (%)* | p value‡ | ||
|---|---|---|---|---|---|
| No gastroenteritis n = 331 | Mild gastroenteritis n = 414 | Severe gastroenteritis n = 153 | |||
| Women | 5 856 (52.0) | 195 (58.9) | 231 (55.8) | 91 (59.5) | 0.01 |
| Age, yr, mean ± SD | 54 ± 11 | 54 ± 10 | 52 ± 9 | 52 ± 10 | 0.002 |
| Neighbourhood income quintile | |||||
| 1–2 (lowest) | 4 311 (38.2) | 103 (31.1) | 132 (31.9) | 54 (35.3) | < 0.001 |
| 3 (middle) | 2 410 (21.4) | 153 (46.2) | 175 (42.3) | 65 (42.5) | |
| 4–5 (highest) | 4 542 (40.3) | 75 (22.6) | 107 (25.9) | 34 (22.2) | |
| Median number of comorbidities§ (IQR) | 3 (2–5) | 4 (2–5) | 4 (2–6) | 4 (2–6) | < 0.001 |
| Hypertension¶ | 1 788 (15.9) | 62 (18.7) | 62 (15.0) | 22 (14.4) | 0.5 |
| Chronic kidney disease¶ | 737 (6.5) | 23 (6.9) | 40 (9.7) | 21 (13.7) | < 0.001 |
| Diabetes** | 609 (5.4) | 12 (3.6) | 24 (5.8) | 9 (5.9) | 0.5 |
| Chronic obstructive pulmonary disease** | 759 (6.7) | 16 (4.8) | 14 (3.4) | 10 (6.5) | 0.03 |
| Hypercholesterolemia** | 2 209 (19.6) | 71 (21.5) | 87 (21.0) | 35 (22.9) | 0.6 |
| Psychiatric history** | 491 (4.4) | 10 (3.0) | 17 (4.1) | 10 (6.5) | 0.4 |
| Median no. of visits to a family physician in the 2 years before outbreak (IQR) | 4 (2–9) | 5 (2–9) | 5 (2–9) | 6 (3–10) | < 0.001 |
Note: IQR = interquartile range, SD = standard deviation.
↵* Unless otherwise indicated.
↵† Assessed at index date (enrollment in the Walkerton Health Study or a randomly assigned date for residents of the surrounding communities).
↵‡ Differences across the 4 groups were analyzed by analysis of variance, Kruskal–Wallis or χ2 tests as appropriate.
↵§ Based on Johns Hopkins Aggregated Diagnosis Groups (assessment period: May 17, 1998, to May 17, 2000).
↵¶ Assessment of hypertension (May 17, 1997, to May 17, 2000) and chronic kidney disease (January 1991, to May 17, 2000) by health care database codes was restricted to the period before the outbreak because these conditions could develop as a result of the outbreak and mediate the relation with cardiovascular disease.
↵** Assessment period: January 1991 to index date.