FluTrack

Data sources

Every number here traces back to the CDC

FluTrack is assembled entirely from the CDC's own respiratory surveillance — the same open, public-domain feeds anyone can download. This page documents each dataset behind the threat level, the license it carries, and why we leave some sources out on purpose.

The Centers for Disease Control and Prevention publish a great deal about respiratory illness every week, all of it in the public domain and all of it downloadable from data.cdc.gov. FluTrack draws on four of those feeds and blends them into a single 0–4 threat level for your state. Nothing below is proprietary, and nothing sits behind a login — you can pull the very same inputs we do and check our work. How the signals are combined is documented separately in our methodology.

The datasets behind the index

Dataset What it measures Granularity License Update cadence
NSSP Emergency Department Visits The share of emergency-department visits coded to influenza, RSV or COVID-19 — the workhorse clinical signal behind the index. State Public Domain Weekly, published Fridays
NSSP Acute Respiratory Illness (ARI) activity level A categorical activity level for acute respiratory illness, reported on a scale from Very Low to Very High. State Public Domain Weekly
NWSS Wastewater Viral Activity Level (WVAL) A normalized viral-activity index built from pathogen concentrations in community wastewater — a leading indicator that can move ahead of clinical signals by days. State / sewershed Public Domain Weekly
NREVSS laboratory test positivity The share of respiratory laboratory tests that come back positive, by virus. HHS region / state Public Domain Weekly

Each source above is a weekly time series, not a live count. Surveillance data is reported with an inherent lag of roughly one to two weeks. FluTrack shows directional trends, not a real-time case count. That is why FluTrack emphasizes the direction of a trend rather than any single week's figure.

How the data reaches your browser

FluTrack runs a two-tier strategy so a page is useful the instant it loads, even if a government feed is briefly unreachable:

  • A bundled snapshot ships with the site and paints immediately. It is clearly labeled as illustrative sample data until a live refresh succeeds.
  • A live refresh then queries the CDC's public-domain Socrata (SODA) endpoints on data.cdc.gov directly from your browser. When it succeeds, the snapshot is replaced and the provenance badge flips from Sample data to Live CDC data.

Because the fetch happens client-side against open government endpoints, the data you see is the data the CDC published — no intermediary server re-hosts or reshapes it. CDC surveillance systems refresh weekly, typically on Fridays, and reported figures generally reflect illness from one to two weeks earlier.

Licensing and what we deliberately exclude

FluTrack uses only public-domain U.S. Government data — the CDC's own surveillance products, which carry no usage restrictions and can be reused by anyone, including on a commercial site. That constraint is a deliberate design choice, not an accident of what was easy to find.

In particular, FluTrack deliberately excludes WastewaterSCAN (also referenced as SCAN or Verily) data. Those wastewater readings are licensed CC BY-NC 4.0 — a non-commercial license. FluTrack is supported by advertising and affiliate links, which makes it a commercial use, so incorporating that data would violate its license terms. We therefore ingest only the CDC's own public-domain NWSS Wastewater Viral Activity Level product and leave the non-commercial networks out entirely.

The exclusion is enforced in code

This is not left to good intentions. The ingestion pipeline runs a defensive source filter — excludeNonCommercial() in src/scripts/data-sources.js — that drops any wastewater row whose provenance references SCAN, WastewaterSCAN, Verily or the other non-commercial networks, so CC BY-NC 4.0 data can never surface on a monetized page even if it appeared in an upstream response.

Independent, not official

Building on the CDC's open data does not make FluTrack a government product. We read the same public feeds available to everyone, with no affiliation, funding relationship, or special access.

No CDC affiliation

FluTrack is an independent project and is not affiliated with, endorsed by, or sponsored by the Centers for Disease Control and Prevention (CDC) or any government agency.

Not medical advice

The information on FluTrack is provided for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition.