Fig. 1

Evidence of antigen of Dirofilaria immitis in dogs by county, grouped according to percent positive tests. Few results (< 30 per year) were received from counties shaded gray, precluding interpretation of the presence of antigen in dogs from these areas. Counties with at least 210 results available for the 7-year period were shaded according to the following code: no dogs reported as positive (0%, white), 0.1–2.0% (light pink), 2.1–4.0% (pink), 4.1–6.0% (red), and > 6.0% (dark red)