Figure 4. Spatial patterning of isolates contained in eight clades identified on the phylogeny of the HA gene segment of A/H1N1 influenza viruses from the 2006–2007 US epidemic that were identified in Figure 1.

Colored rectangles contain individual isolates from the region of the United States associated with that color (see colored map): region 1 (Northeast) is orange, region 2 (Mid-Atlantic) is red, region 3 (South) is yellow, region 4 (Midwest) is green, region 5 (South Central) is blue, and region 6 (West) is purple. Branches leading to background isolates have been removed for clarity.