Weekly Influenza Risk Levels by Chicago ZIP Code

Chicago Department of Public Health provides weekly estimated influenza risk levels for each ZIP Code during flu season. Risk levels from 1 to 10 are calculated by comparing the percentage of Influenza-Like Illness (ILI) to a summer baseline, measured in standard deviations. Data is provisional and compiled via the ESSENCE syndromic surveillance system.

Use Cases

• Analyze spatiotemporal flu trends by mapping ILI_Activity_Level changes across Zip Codes and Census Tracts over time.
• Correlate flu risk (ILI_Activity_Level) with demographic data from other sources using ZIP_Code as a join key.
• Model flu season progression by tracking MMWR_Week and Week_End dates against ILI_Activity_Level for outbreak forecasting.
• Validate syndromic surveillance models by comparing the standard deviation-based ILI_Activity_Level scale against actual case reports.

Strengths

• Data provides granular geographic resolution down to ZIP Code, Community Areas, Wards, and Census Tracts.
• Risk levels are defined using a consistent statistical method based on standard deviations from a seasonal baseline.
• Time-series data covers the entire flu season from MMWR week 40 to week 20 of the following year.

Limitations

• Row count and sample size are unknown, limiting assessment of statistical power.
• Data is provisional and subject to change, which may affect reproducibility of analyses.
• Geographic coverage is limited solely to Chicago, restricting broader applicability.

Provenance

Source

data.cityofchicago.org, compiled via the ESSENCE syndromic surveillance system.

Collection Method

Estimates based on observed levels of Influenza-Like Illness (ILI) from syndromic surveillance.

Time Range

Weekly data during flu season (MMWR week 40 to week 20 of the following year).

Freshness

Updated as of April 2026, indicating regular updates.

Geography

ZIP Codes within Chicago, Illinois, USA.