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Outbreak health data by decade.
| Decade | Median Case Count (n) | Total Case Count | Median Attack Rate (n) |
|---|---|---|---|
| Pre-1920 | 303 (14) | 30,330 | N/A (0) |
| 1920s | 27 (263) | 95,610 | 5.3% (9) |
| 1930s | 23 (178) | 46,179 | 10.5% (13) |
| 1940s | 370 (36) | 71,839 | 26.4% (4) |
| 1950s | 71 (39) | 95,094 | 8.7% (13) |
| 1960s | 170 (25) | 30,732 | 11.3% (11) |
| 1970s | 59 (212) | 77,585 | 36.2% (18) |
| 1980s | 59 (323) | 149,486 | 28.0% (51) |
| 1990s | 63 (241) | 641,243 | 28.0% (45) |
| 2000+ | 71 (188) | 112,980 | 12.5% (50) |
