Methodology

How lettuce-watch sources outbreak data, links to primary sources, and applies underdiagnosis multipliers to convert reported case counts to estimated community case counts.

Data sources

Outbreak records come from authoritative public datasets, prioritized by recency and traceability:

• CDC NORS — National Outbreak Reporting System. Historical structured data with 12–18 month reporting lag. data.cdc.gov SODA API.
• FDA CORE — Coordinated Outbreak Response & Evaluation. Active FDA-led investigations, updated weekly.
• CDC multistate outbreak notices — Public advisory pages when active investigations warrant consumer notice.
• USDA-FSIS recalls — Public Health Alerts and Class I/II/III recalls for meat, poultry, and egg products.
• openFDA Food Enforcement — JSON API for FDA recall and enforcement records.
• NCBI Pathogen Detection — Whole-genome sequencing cluster linkage for cross-state outbreak detection.

Underdiagnosis multipliers

Reported case counts are laboratory-confirmed and reported to public health agencies. They represent a fraction of the true community case count because:

• Many cases resolve without medical care.
• Of those that seek care, only a subset is tested.
• Of those tested, only a subset is reported to NORS.

Scallan et al. (2011) estimated pathogen-specific multipliers — STEC O157 26.1×, Salmonella 29×, Shigella 33×, Norovirus ~10×, Listeria ~2×. lettuce-watch displays reported counts, not adjusted estimates, to preserve the primary signal.

Traceback chain visualization

Each outbreak dossier includes a 4-node traceback chain: farm → processor → distributor → retailer. The chain is rendered horizontally with implicated nodes highlighted in amber and dashed "unknown" placeholders for steps where the public investigation has not disclosed operator names.

Honest gap nodes are a feature, not a bug. When the FDA traceback has not named a specific farm or processor, the dossier shows a dashed placeholder rather than fabricating an intermediate node.

Cluster linkage

When whole-genome sequencing (WGS) links cases across states, the outbreak is treated as a single event with cross-state cluster linkage. NCBI Pathogen Detection cluster IDs are surfaced when known.

Citation requirement

Every outbreak dossier links at least three sources, drawn from: agency investigation pages (CDC MMWR, FDA Environmental Assessment, USDA-FSIS recall notices), peer-reviewed papers, or state press releases.

Severity ladder

Severity is communicated as a text label, not an emoji, and is paired with a pattern (color + stroke style) so the signal is preserved for color-blind readers:

• active · multistate — ongoing, ≥2 states, cluster confirmed
• active · single-state — ongoing, 1 state
• under investigation — pathogen/matrix suspected, not confirmed
• closed — resolved, no new cases ≥42 days
• closed · recalled — resolved, recall issued

Data provenance status (Phase 1b)

Real public-data ingestion is live for the historical and investigation layers. The CDC NORS historical extract, the FDA CORE weekly investigation table, and the openFDA food-enforcement fallback are ingested by tested adapters (scripts/ingest_*.py), and every record carries its source URL, source system, retrieval timestamp, and official/unofficial status. The USDA FSIS Recall API is WAF-blocked from data-center IPs; rather than fabricate meat-recall data, the FSIS job records the block and falls back to openFDA (FDA-regulated food only), labelled as such.

The individual outbreak dossiers on this site remain hand-curated editorial write-ups of well-documented events, each citing its primary sources. They are not auto-generated from the feeds above; the machine-ingested layers are the NORS, CORE, and openFDA datasets surfaced in the "Data as of" table above.