Volume 19, Number 6—June 2013
Research
Active Surveillance for Influenza A Virus among Swine, Midwestern United States, 2009–2011
Figure 4
![Age distribution of groups of pigs that were positive or negative for influenza A, determined by real-time reverse transcription PCR, midwestern United States, June 2009–December 2011.](/eid/images/12-1637-F4.jpg)
Figure 4. . Age distribution of groups of pigs that were positive or negative for influenza A, determined by real-time reverse transcription PCR, midwestern United States, June 2009–December 2011.
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