Questions about FluTrack, answered

It is a rating — from Minimal to Very High — of available flu, RSV and COVID-19 surveillance inputs for a state. It summarizes the dated observations, with a trend only when enough comparable history exists. It is not an influenza-only level, an infection count, a forecast or a personal risk score. Sample data is illustrative, and missing or stale observations cannot establish current conditions. Our methodology documents the calculation.

The index sources generally publish weekly, with source-specific schedules and reporting delays. Surveillance data is reported with an inherent lag of roughly one to two weeks. FluTrack shows directional trends, not a real-time case count. The observation period is separate from publication and retrieval dates: fetching September observations in October does not establish October conditions. The newest figures can be revised, and an older observation may still be the latest scheduled release.

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.

The model scores available wastewater viral activity, emergency-department visits and the Acute Respiratory Illness activity label from 0 to 100, blends them with fixed weights and maps the result to five levels. Laboratory positivity has a model weight but no live adapter; it appears only in illustrative samples. The trend compares the latest observation with the mean of up to three prior observations, not an ordinary week-over-week change. With insufficient history the trend is unknown. See our methodology for each weight and threshold.

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.

The implemented live index feeds are NSSP emergency-department visits and the Acute Respiratory Illness activity level, and NWSS wastewater viral activity, from data.cdc.gov through the existing ingestion service. Only usable observations contribute to a reading. NREVSS laboratory positivity is unavailable live; sample inputs are labeled as illustrative. Hospital admissions in the area card come from NHSN and are a separate measure, outside the index. Our data sources page documents each feed.

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.

The CDC's National Wastewater Surveillance System (NWSS) measures viral material in wastewater to produce a normalized activity index. It describes participating sewersheds, not infection counts, test positivity, ED visits or hospital admissions. Coverage differs across places and viruses; a local wastewater increase cannot establish a statewide or national trend. FluTrack's wastewater weight is an editorial choice documented in our methodology.

It is the CDC's own epidemic-trend category for COVID-19, not a FluTrack rating. The CDC's Center for Forecasting and Outbreak Analytics estimates the reproduction number (Rt) from emergency-department visits and assigns a category from the probability that infections are growing: Growing (more than 90%), Likely growing (75% to 90%), Not changing (25% to 75%), Likely declining (10% to 25%) and Declining (less than 10%). The CDC says these categories show direction only and do not reflect the burden of disease. FluTrack shows the category separately from its combined respiratory index, with the model report's date and the date its data end, and never adds it to the index. See how it is shown.

They measure different things in different ways. The CDC's epidemic trend is a modeled direction estimated from emergency-department visits. Wastewater viral activity comes from sampling sites and follows its own reporting schedule. FluTrack's own trend compares the latest observation with the mean of up to three prior observations of one measurement. A level can also be high while a direction is declining, or low while it is growing. When a state page lists measurements that point in opposite directions it says so rather than averaging them, and it notes that the CDC's model and the emergency-department share come from the same data, so their agreement is not independent confirmation. Changes in reporting coverage can also affect comparisons between weeks.

No. Surveillance gaps describe missing coverage, not the absence of illness. Missing values are not zeros, an unavailable pathogen is not rated low, and insufficient history is not holding steady. A state or metro reading cannot substitute for independently measured city conditions, and a national trend cannot substitute for the selected state.

WastewaterSCAN / SCAN data is licensed CC BY-NC 4.0, which permits non-commercial use only; FluTrack excludes it because the project is designed for commercial use. The existing conservative provenance filter also excludes Verily-marked rows. A provider name does not establish a dataset's license: the CDC's September 28, 2026 Verily testing-contract award is distinct from the WastewaterSCAN license and does not automatically identify its data as WastewaterSCAN data. Our data sources page explains the filter and its coverage limits.

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.