How to read an outbreak investigation
Every outbreak page on Public Health Trace republishes fields from an official investigation record -- CDC's NNDSS/NORS surveillance data, an FDA CORE investigation, or a state health department. This guide explains what each part of that record means, so a page's status badges and numbers read the same way a public health investigator would read them.
Investigation status
Not every source publishes a clean "is this active" field, so Public Health Trace computes one consistently based on where a record came from and what the source has actually reported (see methodology):
- Active / Under investigation
- A formally-tracked investigation (for example, an FDA CORE investigation) with no recorded end date and not reported as closed by the source. A recent CDC Health Alert Network bulletin or WHO notice (published within roughly the last month) is also shown as active.
- Monitoring
- Reserved for surveillance-derived signals -- CDC NNDSS case counts exceeding their own historical baseline. This is a statistical comparison, never a confirmed outbreak, and is always shown with an explanation of the baseline it's being compared against.
- Resolved
- A formally-tracked investigation that has a recorded end date or has been reported as closed by the source.
- Historical record
- CDC NORS records, which document past outbreaks that were formally investigated and reported after the fact, are always shown as historical -- NORS is a closed-book archive, not a live case-tracking feed, so this doesn't depend on how recently the outbreak itself occurred. An older Health Alert Network bulletin or WHO notice is also shown as historical once it ages past the recent window above.
Provisional vs. final data
A record marked provisional means the source agency may still revise it -- most commonly, case counts for a recent outbreak that CDC continues to update as local and state health departments finish reporting. A provisional record is not less credible; it is a disclosed snapshot of an investigation still in progress. Once an agency stops updating a record, Public Health Trace continues to show its last reported values rather than guessing at a final count.
Cases, hospitalizations, and deaths
These are the counts as published by the source agency at the time Public Health Trace last imported the record -- never estimated, interpolated, or adjusted. A blank hospitalization or death count means the source didn't report that figure for this outbreak, not that the true count is zero. Case counts for an active investigation typically rise over time as more illnesses are confirmed and linked; a later, lower count on a historical record usually reflects a source correction, not new information reducing real harm.
Reported food vehicle
A "food vehicle" is the food product investigators have published as suspected or confirmed to be the source of illness. This reflects the investigating agency's own published finding -- it is not a medical diagnosis, and Public Health Trace does not independently verify or infer a food vehicle beyond what the source has stated.
Linked recalls and CDC announcements
An outbreak page may show related recalls or CDC announcements below the main record. Some of these relationships are explicitly confirmed by a real, source-published link between the two records; others reflect a text-based match (for example, the same food name appearing in both a recall and an outbreak) that hasn't been confirmed as the same event. See how recalls and outbreaks are connected for exactly how that distinction works and where it's labeled on the page.
Always check the official source
Every outbreak page links directly to the official source record. Public Health Trace organizes and cross-references this data for readability -- it is not affiliated with the CDC, FDA, or any state health department, and the source's own page is always the authoritative, most current version. See our medical disclaimer for what this site is not: a diagnosis tool or a substitute for medical advice.
