Table 1.

Characteristics of cases.

Risk Factor	N = 4720
Age
<35 years (%)	1.7
35–70 years (%)	41.3
≥70 years (%)	57.0
Sex
Male (%)	60.6
Female (%)	39.4
Medical history
Hypertension (%)	32.3
Respiratory disorders (%)	24.6
Diabetes mellitus (%)	27.0
Heart disease (%)	35.7
Stroke (%)	17.3
Season of onset
Warm (April to September, %)	43.3
Cold (October to March, %)	56.7