2.
NoV检出的季节分布[n（%）]
| 季节 | n | 阳性检出率 |
| 春季(3~5月) | 210 | 45(21.4) |
| 夏季(6~8月) | 148 | 22(14.9) |
| 秋季(9~11月) | 136 | 47(34.6) |
| 冬季(1月、2月、12月） | 264 | 127(48.1) |
| χ2值 | 68.837 | |
| P值 | < 0.001 |
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