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COVID Flow

COUNTY SURVEILLANCE

Cook County

Cook County and Chicago-area sewersheds. A metro-focused view of community viral shedding in wastewater.

Activity index

-1.98

Week over week -8.3%

Stable

Updated Jul 27, 2026

Current metrics

Activity index

-1.98

Week-over-week -8.3%

Compared to each sewershed's own history (0 = typical week)

Sites reporting

16

16 of 19 registered sewersheds · 6.8M population represented

Data quality

86%

Latest week composite score. See quality panel for flags.

How to read the activity index

01

Near zero

Typical shedding for that sewershed compared with its own history.

02

Below zero

Less viral RNA than the historical baseline for that location.

03

Above zero

More viral RNA than the historical baseline for that location.

Week-over-week change shows direction only. Trend labels (rising, falling, stable) apply only when enough samples meet our quality thresholds.

Historical trend

Weekly community wastewater signal for Cook County, aggregated from CDC NWSS sewershed samples after cleaning and quality review.

Wastewater activity over time
Weekly weighted activity index for Cook County. Higher values indicate elevated viral RNA relative to the regional baseline.

Source: CDC NWSS via COVID Flow weekly pipeline. Index is relative to historical sewershed baselines, not a case count.

Sewershed sites

Site-level activity for the latest reporting week. Each row is one wastewater monitoring location connected to the public sewer network.

16 of 19 sewersheds reported for the week of Jul 27. Sorted by activity index (highest first).

Site IDCounties servedActivityWoWTrendQualityLast sample
428Cook-0.94+116.1%Rising100%Jul 29
418Cook-0.95+98.2%Rising100%Jul 30
414Cook-1.04+72.6%Rising100%Jul 29
429Cook-1.10+139.3%Rising85%Jul 29
425Cook-1.40+60.7%Rising100%Jul 29
430Cook-1.64+39.8%Rising85%Jul 29
416Cook-1.67-23.1%Stable85%Jul 29
431Cook-1.72-58.0%Falling85%Jul 29
427Cook-1.78+67.2%Rising85%Jul 30
417Cook-1.85-72.1%Falling85%Jul 29
422Cook-1.89-49.8%Falling100%Jul 30
413Cook-2.15-31.8%Falling65%Jul 29
424Cook-2.17-43.5%Falling80%Jul 30
421Cook-2.18-53.1%Falling85%Jul 30
423Cook-2.35-36.1%Falling65%Jul 29
419Cook-2.73-109.5%Falling65%Jul 29

Quality and provenance

Data quality
How complete and reliable the underlying wastewater samples are for the latest reporting week. Lower scores mean more caution when interpreting trends.
86%quality score
  • Some samples below limit of detection
  • Sample location is not a wastewater treatment plant
  • Missing flow or population normalization
  • Grab sample rather than composite collection

Wastewater monitoring reflects community shedding, not individual diagnoses. Gaps in sampling, lab methods, or sewershed coverage can shift the index without a true epidemic change.

Data provenance
Metrics are rebuilt each week from CDC NWSS open data. We harmonize sewershed identifiers, apply Illinois cleaning rules, and roll samples up to site and region level. Cook County views use Illinois-focused cleaning rules before publishing to this dashboard.

Source: CDC NWSS program

Projected trend (next few weeks)

Our best estimate of where the wastewater activity index for Cook County is heading over the next few weeks, shown with an uncertainty band. This tracks wastewater activity, not confirmed case counts.

Short-horizon forecast
Ensemble baseline for Cook County from the week of Jul 27. Shaded band ≈ 80% interval from backtest errors.

Viewing: Ensemble baseline

Rising
ObservedEnsemble~80% interval

1-week outlook (ensemble_v1): Rising · confidence high. Surveillance context only, not for clinical decisions.