Table 3.

The grade distributions of the student cases in the outbreak

Grade	Number	Cases	Attack rate (%)
1	182	28	15.38
2	175	30	17.14
3	166	28	16.87
4	158	44	27.85
5	150	53	35.33
6	173	8	4.62
7	171	22	12.87
8	132	15	11.36
9	118	10	8.47
10	94	11	11.70
11	95	5	5.26
12	79	0	0.00
Total	1693	254	15.00