Association between meteorological events and epidemic days
| Epidemic days | Control days | Odds ratio (95% CI) | |
| Thunderstorms within 80 km | 15/481-150(31%) | 16/191 (8%) | 5.0 (2.4 to 10.5) |
| Thunderstorm outflows | 13/39 (33%) | 5/155 (3%) | 15.0 (6.0 to 37.6) |
| Thunderstorms within 80 km on days when there was no outflow detected | 4/26 (15%) | 10/150 (7%) | 2.5 (0.8 to 8.5) |
| Cold front | 4/39 (10%) | 24/155 (15%) | 0.6 (0.2 to 1.9) |
↵1-150 Number of epidemic or control days on which the meteorological event occurred/number of epidemic or control days for which the relevant meteorological data were available.