Questions about FluTrack, answered

It is a single, plain-English rating — from Minimal to Very High — that summarizes how much combined flu, RSV and COVID-19 activity the CDC's surveillance data shows in a given state, paired with a trend of whether that activity is rising, falling or holding steady. It is a descriptive summary of recently reported data — not a forecast, not a case count, and not a measure of any one person's risk. Our methodology documents exactly how it is built.

FluTrack refreshes weekly. CDC surveillance systems publish on a weekly cadence, typically on Fridays, and each refresh reflects the most recent reporting week available. Surveillance data is reported with an inherent lag of roughly one to two weeks. FluTrack shows directional trends, not a real-time case count. Because reporting is collected and revised over time, the newest figures describe recent weeks rather than the current day.

Surveillance figures are assembled from thousands of hospitals, laboratories and wastewater sites, then cleaned, aggregated and revised before the CDC publishes them. That pipeline takes time, so a given week's numbers generally reflect illness from one to two weeks earlier, and the most recent week or two can still shift as late reports arrive. Surveillance data is reported with an inherent lag of roughly one to two weeks. FluTrack shows directional trends, not a real-time case count. This is why FluTrack leads with the direction of travel rather than any single day's number.

Four public-domain CDC signals — wastewater viral activity, emergency-department visits, an acute-respiratory-illness activity label, and laboratory test positivity — are each scored from 0 to 100, blended by fixed weights into one composite score, and mapped to one of five levels. A separate rule compares the latest week against the prior few to set the trend. Every weight, threshold and cut point is published on our methodology page, so the calculation can be checked rather than taken on faith.

A surge alert is an optional email that flags when CDC data shows respiratory activity climbing in a state you follow. You pick a state, and FluTrack emails you when the trend for that state turns upward — at most about once a week, and never more often than the data warrants. You can set one up on the surge alerts page and unsubscribe at any time. The alert reports what the data shows; it does not advise a course of action.

Entirely from the CDC's own public-domain surveillance systems: NSSP for emergency-department visits and the acute-respiratory-illness activity level, NWSS for wastewater viral activity, and NREVSS for laboratory test positivity. All of it is downloadable by anyone from data.cdc.gov. Our data sources page documents each feed, and our methodology explains how they are combined.

Because a precise, real-time case count does not exist in this data. Modern respiratory surveillance measures activity through proxies — the share of ER visits, test positivity, wastewater concentrations — rather than a confirmed tally of every infection, and each figure carries a reporting lag and later revisions. A single hard number would imply a precision the data cannot support, so FluTrack reports a directional level and trend instead. Surveillance data is reported with an inherent lag of roughly one to two weeks. FluTrack shows directional trends, not a real-time case count.

Communities shed traces of respiratory viruses into their sewage, and the CDC's National Wastewater Surveillance System (NWSS) measures those concentrations to produce a normalized viral-activity level. It carries weight because it does not depend on who chooses to get tested, and it can move ahead of clinical signals by several days — making it one of the earliest reads on where activity is heading. For that reason FluTrack weights it most heavily of the four signals; the exact weight is on our methodology page.

Some widely cited wastewater networks — WastewaterSCAN, also referenced as SCAN or Verily — publish under a CC BY-NC 4.0 license, which permits non-commercial use only. FluTrack is supported by advertising and affiliate links, which makes it a commercial use, so incorporating that data would breach the license terms. FluTrack therefore ingests only the CDC's own public-domain NWSS product and filters the non-commercial networks out in code. Our data sources page explains the exclusion in full.

The underlying CDC surveillance data is public-domain U.S. Government work and free for anyone to reuse — you can pull the same feeds directly from data.cdc.gov. FluTrack's presentation of it — the threat-level wording, the editorial thresholds, the design and the copy — is our own work; please attribute FluTrack and link back rather than republishing pages wholesale. For specific reuse, licensing or partnership questions, contact us.

No. 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. FluTrack is a data-visualization utility that describes what public surveillance data shows in aggregate; it does not diagnose, treat, or recommend any course of action.

No. 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. FluTrack is built on the CDC's open, public-domain data, but building on government data does not imply that the government endorses this site.

FluTrack is free to use and is supported by advertising and clearly disclosed affiliate links, where we may earn a commission on qualifying purchases at no extra cost to you. That revenue never influences the threat levels we report: the index is computed the same way regardless of who advertises, and it always reflects the CDC's figures alone. Our affiliate disclosure explains the arrangement in full.

FluTrack works without a login, and you never need an account to view any threat level. If you sign up for surge alerts, your email address is used only to send the alerts you asked for, and you can unsubscribe at any time. The full details of what is collected and how it is handled are in our privacy policy.