Number of swine flu cases per county.  Mostly June 19 2009 but some state data is up to one month out of date.  Utah, Virginia, and Minnesota are colored according to health service zones made up of several counties, each of which is colored by the average value - average below 1.0 is not colored.  See "references and notes" below for full details.
The color scheme is green -&gt; red -&gt; black with successive shades beginning at powers of 2 (1, 2, 3-4, 5-8 ... to 1024-2048 for Chicago and New York).  See legend below.

This file is based on the public domain blank U.S. map with counties labeled by FIPS code, file:USA Counties with FIPS and names.svg.  It can be colored by opening the .svg in a text editor and adding FIPS codes before the appropriate fill color.
USA_counties_FIPS_text_addressable.svg
USA_counties_FIPS_text_addressable.svg: Mike Serfas / * derivative work: Mike Serfas (talk)