Influenza Risk Level by ZIP Code

Estimates are made during flu season, which goes from MMWR week 40 to week 20 of the following year. The risk level is based on observed level of Influenza-Like Illness (ILI).

ILI Activity Level is determined as follows: ILI percentage for each ZIP Code for the week is compared to the mean ILI percentage during the non-influenza months (summer months). Level 1 corresponds to an ILI percentage below the mean, level 2 to an ILI percentage less than one standard deviation (SD) above the mean, level 3 to an ILI percentage more than one, but less than two SDs above mean, and so on, with level 10 corresponding to an ILI percentage more than eight SDs above the mean.