Volume 19, Number 6—June 2013
Research
Active Surveillance for Influenza A Virus among Swine, Midwestern United States, 2009–2011
Figure 1

Figure 1. . Swine influenza virus group status for 32 pig farms participating in an active surveillance project, midwestern United States, June 2009–December 2011. Each horizontal line represents a farm, each dot represents a sampling event, and colors indicate virus status of the group.