Table 1 Summary of case and control matching variables
| Â | Cases | Controls | Total (%) |
|---|---|---|---|
All subjects | 217 | 217 | 434 |
Gender | Â | Â | Â |
   Male | 134 | 134 | 268 (62) |
   Female | 83 | 83 | 166 (38) |
Age strata | Â | Â | Â |
   0-4 years | 31 | 31 | 62 (14) |
   5-9 years | 104 | 104 | 208 (48) |
   10-14 years | 47 | 47 | 94 (22) |
   15-19 years | 35 | 35 | 70 (16) |
Season | Â | Â | Â |
   Summer | 32 | 32 | 64 (15) |
   Autumn | 58 | 58 | 116 (27) |
   Winter | 70 | 70 | 140 (32) |
   Spring | 57 | 57 | 114 (26) |