Volume 19, Number 6—June 2013
Research
Active Surveillance for Influenza A Virus among Swine, Midwestern United States, 2009–2011
Table 2
Influenza virus status among growing pigs, by season, midwestern United States, June 2009–December 2011
Season | Influenza virus status, no. groups |
Total, no. groups | |
---|---|---|---|
Positive | Negative | ||
Winter | 19 | 105 | 124 |
Spring | 37 | 100 | 137 |
Summer | 40 | 110 | 150 |
Fall | 21 | 108 | 129 |
Total | 117 | 423 | 540 |