Table 1. Comparison of hospital influenza outbreak characteristics across the 2012-13 to 2015-16 seasons in Ontario.
| Outcome | Influenza season | |||
|---|---|---|---|---|
| 2012–13 | 2013–14 | 2014–15 | 2015–16 | |
| Total number of outbreaks | 65 | 38 | 117 | 36 |
| − Influenza A: n (%) | 63 (96.9%) | 16 (42.1%) | 112 (95.7%) | 27 (75.0%) |
| − Influenza B: n (%) | 2 (3.1%) | 22 (57.9%) | 5 (4.3%) | 9 (25.0%) |
| Number of hospital sites reporting ≥1 outbreaks (% of total sites) | 45 (19.6%) | 30 (13.0%) | 72 (31.3%) | 29 (12.6%) |
| Median number of outbreaks per hospital site with an outbreak | 1.0 | 1.0 | 1.0 | 1.0 |
| − Range | 1–6 | 1–2 | 1–7 | 1–4 |
| Median duration of outbreaks in days | 5.0 | 4.5 | 5.0 | 6.0 |
| − Range | 0–29 | 1–20 | 0–32 | 0–16 |
| Total number of outbreak cases per season | 465 | 179 | 753 | 189 |
| Median number of cases per outbreak | 5.0 | 3.0 | 5.0 | 5.0 |
| − Range | 1–45 | 2–11 | 2–60 | 1–14 |
| Median percent case attack rate by at-risk area | 16.1% | 18.5% | 15.9% | 18.0% |
| − Range | 4.1–70.8% | 4.4–75.0% | 4.1–66.7% | 4.5–36.8% |
| Number of pneumonia cases (% of cases)a | 25 (5.4%) | 15 (8.4%) | 46 (6.1%) | 5 (2.6%) |
| Number of fatal cases (% of cases)a | 12 (2.6%) | 3 (1.7%) | 18 (2.4%) | 7 (3.7%) |
Abbreviation: n, number
a Based on the total number of cases (n=1,586)