Flu illness tracking season officially kicks off with Walgreen's latest Flu Index

Walgreens on Wednesday launched its first Flu Index for the 2017-18 season. The Flu Index is a weekly report that ranks the top markets and states for flu activity in the U.S., including Puerto Rico. Brownsville and Beaumont, Texas are among the top markets for flu this week, and Texas and Arkansas top the list of U.S. states with the most flu activity.