Figure 6.18 Geographical development of the swine flu pandemic in the United States, 2009–10
influenza season. Each histogram shows the number of positive influenza virus
isolates by Department of Health and Human Services regions reported by WHO/NREVSS
Collaborating Laboratories. The preponderance of swine flu A(H1N1), shown in black,
as opposed to normal seasonal strains (grey) is evident in all regions.