GCRI · Science
Epidemiology and public health science
Epidemiology studies the distribution and determinants of health and disease in populations. It provides the evidence used to detect outbreaks, estimate burden and evaluate interventions. Health Nexus stewards this page for the Nexus Consortium.
01Register
Epidemiology and public health science on the record.
The Global Centre for Risk and Innovation
- 01InstitutionThe Global Centre for Risk and Innovation (GCRI)
- 02The methodWhat epidemiology and public health science covers
- 03Reference practiceEpidemiological practice is governed by reporting standards and international health law
- 04In systemic risk workTransmission meets supply chains and behaviour
- 05Applied inPlatforms that apply this method
- 06StewardshipWho maintains this page
- 07SourcesWhere this page’s references lead
02The method
What epidemiology and public health science covers.
- 01
Core methods
cohort and case-control studies; disease surveillance; transmission modelling; outbreak investigation; burden of disease estimation; spatial epidemiology.
- 02
Data and instruments
notifiable disease reporting systems; hospital and laboratory records; household and health surveys; vital registration; genomic surveillance.
- 03
Validation
Findings are checked through replication, sensitivity analyses and comparison of independent surveillance streams. Transmission models are assessed by out-of-sample forecasting of case counts.
- 04
Limits
Reporting delays, under-ascertainment and confounding bias estimates. Behaviour change during outbreaks alters the parameters models rely on.
- 05
Use in risk decisions
Epidemiological evidence informs preparedness, resource allocation and the economic consequences of disease. It shows how health shocks interact with travel, labour, supply chains and public finance.
03Geography
Environmental exposure worldwide.
Population density, daytime surface heat and haze across the world, from NASA GIBS. Each layer carries its own date.
The interactive map needs JavaScript; the layer list and sources are below.
Layers 3
Environmental exposure, for this page
About this layer
- Evidence
- Estimated
- Source
- Gridded Population of the World v4.11 (NASA SEDAC (CIESIN, Columbia University))
- Provider
- NASA SEDAC (CIESIN, Columbia University)
- Licence
- CC BY 4.0
- Vintage
- null; Census-based estimate, static (2020)
- Resolution
- about 1 km grid
- Uncertainty
- Census-based estimate of people per square kilometre in 2020, shown as exposure context; not a count of people affected by any hazard.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Observed (persistent cloud still leaves gaps)
- Source
- VIIRS NOAA-20 Level 3, 8-day (NASA LANCE)
- Provider
- NASA LANCE
- Licence
- NASA open data
- Vintage
- 8-day; Satellite 8-day composite; persistent cloud still leaves gaps
- Newest at build
- 2026-09-14
- Resolution
- about 1 km grid
- Uncertainty
- Satellite skin temperature of the ground over the 8 days ending on the date shown, a heat exposure indicator; not air temperature, heat index or a heat warning.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Observed (clouds leave gaps)
- Source
- VIIRS NOAA-20 Deep Blue AOD (NASA LANCE)
- Provider
- NASA LANCE
- Licence
- NASA open data
- Vintage
- daily; Satellite retrieval; clouds leave gaps
- Newest at build
- 2026-10-14
- Resolution
- about 2 km grid
- Uncertainty
- Satellite measure of haze, smoke and dust through the whole air column on the day shown; an exposure indicator, not ground-level PM2.5, an air quality index or a health warning.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Observed
- Source
- VIIRS NOAA-20 corrected reflectance (NASA LANCE)
- Provider
- NASA LANCE
- Licence
- NASA open data
- Vintage
- daily; Satellite image
- Newest at build
- 2026-10-14
- Resolution
- about 250 m grid
- Uncertainty
- Satellite image. Satellite or model raster as the provider publishes it. Clouds, swath gaps and retrieval error leave gaps and noise; values are indicators, not measurements at a place.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Observed (clouds leave gaps)
- Source
- OMI Aura (NASA GES DISC)
- Provider
- NASA GES DISC
- Licence
- NASA open data
- Vintage
- daily; Satellite retrieval; clouds leave gaps
- Newest at build
- 2026-10-10
- Resolution
- about 2 km grid
- Uncertainty
- Satellite column of nitrogen dioxide in the lower atmosphere on the day shown, mostly from combustion; not a ground-level concentration or a health warning.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Modelled (latest year GIBS publishes)
- Source
- MODIS Terra and Aqua land cover (MCD12Q1) (NASA LP DAAC)
- Provider
- NASA LP DAAC
- Licence
- NASA open data
- Vintage
- yearly; Satellite classification; latest year GIBS publishes
- Newest at build
- 2024-01-01
- Resolution
- about 500 m grid
- Uncertainty
- Satellite land cover classes for the year shown, including croplands; a classification with known errors, not a farm register.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
Keyboard, with the map focused
Hold Ctrl or ⌘ and scroll to zoom
Latest available
NASA GIBS / EOSDIS · ASTER GDEM (METI, NASA) · Blue Marble (NASA) · © OpenStreetMap contributors (ODbL) · Natural Earth
Loading the latest NASA imagery.
Drag to move. Ctrl or ⌘ and scroll, pinch or the buttons to zoom; hover for the values under the pointer; reset returns to the region.
Environmental exposure, framed on the world.Satellite and model products as NASA publishes them, each with its own date. They are indicators, not assessments of any place.
Data: NASA GIBS · ASTER GDEM · Blue Marble · © OpenStreetMap contributors · Natural Earth · NASA EONET · NASA JPL OPERA DIST-ALERTSources and licences
- We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS). Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS). Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- Center for International Earth Science Information Network (CIESIN), Columbia University. 2018. Gridded Population of the World, Version 4 (GPWv4): Population Density, Revision 11. NASA Socioeconomic Data and Applications Center (SEDAC). Licensed under CC BY 4.0. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). doi:10.7927/H49C6VHW. CC BY 4.0
- VIIRS near-real-time products (flood, land surface temperature, snow cover, corrected reflectance), NASA LANCE; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- MODIS and VIIRS atmosphere products, NASA LANCE and LAADS DAAC; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- OMI nitrogen dioxide (Aura) and OMPS aerosol index (Suomi NPP), NASA; distributed by the NASA GES DISC; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- MODIS land products (vegetation indices, gross primary production, land cover), NASA LP DAAC and LANCE; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- ASTER GDEM is a product of METI and NASA (ASTER Global Digital Elevation Model V003, NASA LP DAAC); imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). Cite as: NASA/METI/AIST/Japan Spacesystems and U.S./Japan ASTER Science Team (2019). ASTER Global Digital Elevation Model V003. doi:10.5067/ASTER/ASTGTM.003. NASA open data
- Made with Natural Earth. Free vector and raster map data @ naturalearthdata.com. Public domain
- © OpenStreetMap contributors (ODbL), via NASA GIBS (coastlines, boundaries, roads and place names). Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). ODbL
- Blue Marble, NASA Earth Observatory; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- Context on the globe and flat map: coastlines, boundaries, roads and place names from NASA GIBS reference layers (OpenStreetMap data, ODbL, © OpenStreetMap contributors); Blue Marble imagery as an optional base; 3D terrain and the elevation read-out from the ASTER GDEM elevation colour index (5 m to 200 m classes, exaggerated for legibility). Boundaries are drawn as published and imply no position on any territory.
- Live events: NASA Earth Observatory Natural Event Tracker (EONET); events are indicative and keep their original source links.
- Live: NASA EONET Events are indicative, not authority warnings.
- Observed (EO): NASA JPL OPERA DIST-ALERT (contains modified Copernicus Sentinel data 2026). We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS).
- NASA GIBS: We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS).
- Air quality forecast, 5 days, PM2.5 (CAMS via Open-Meteo): Contains modified Copernicus Atmosphere Monitoring Service information 2026.
- Past year, daily temperature (ERA5 via Open-Meteo): Contains modified Copernicus Climate Change Service information 2026.
- Weather data by Open-Meteo.com (https://open-meteo.com/), licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).
- Optional layers (14 sources in the layer list: live, forecast, observed and context) print their provider credit on the map and here when switched on; forecasts are model output and derived indices are estimates.
Layers and dates
- Population density, 2020: Population: CIESIN, Columbia University, Gridded Population of the World v4.11 (2018), NASA SEDAC, CC BY 4.0 · static
- Land surface temperature, day, 8-day composite: VIIRS NOAA-20 Level 3, 8-day, NASA LANCE · 14 Sep 2026
- Aerosol optical depth, daily: VIIRS NOAA-20 Deep Blue AOD, NASA LANCE · 13 Oct 2026
- True colour: VIIRS NOAA-20 corrected reflectance, NASA LANCE · 13 Oct 2026
- Nitrogen dioxide, lower atmosphere column: OMI Aura, NASA GES DISC · 10 Oct 2026
- Land cover type (IGBP), yearly: MODIS Terra and Aqua land cover (MCD12Q1), NASA LP DAAC · 2024
04Reference practice
Epidemiological practice is governed by reporting standards and international health law.
| Reference | What it sets |
|---|---|
| International Health Regulations (2005) | Surveillance and notification duties of states |
| EQUATOR guidelines (STROBE, CONSORT) | Reporting standards for observational studies and trials |
| GRADE | Rating certainty of evidence for recommendations |
| WHO Global Influenza Surveillance and Response System | Laboratory network for influenza surveillance |
05Process
How the process runs.
Process
Epidemiology and public health science: IHR event detection and notification
Under the IHR (2005), a State Party assesses events with the Annex 2 instrument and notifies WHO through its National IHR Focal Point.
01 Surveillance
- 01Indicator-based surveillanceSource · State PartyRoutine reporting, such as case reports, is one signal source. Article 5 requires capacity to detect, assess, notify and report events.
- 02Event-based surveillanceSource · State Party · WHOUnstructured signals, such as media or community reports, are another source. WHO may use such reports and then seeks verification.
02 Event handling
- 03TriageStepSignals are screened for relevance and duplicates before follow-up. The Regulations prescribe no triage method; this is general practice.
- 04Verify with the sourceStep · State PartyWhen WHO requests verification, the State Party replies within 24 hours with an acknowledgement and the public health information available.
03 Assessment
- 05Rapid risk assessmentModelA rapid assessment of hazard, exposure and context can support the response. It is separate from Annex 2 and not in the text read.
- 06Annex 2 decision instrumentGate · State PartyThe State Party assesses each event with the Annex 2 algorithm, on impact, novelty, international spread and restrictions.
04 IHR focal point
- 07Notify WHODecision · State Party, through its National IHR Focal PointThe State Party notifies WHO within 24 hours of assessment, through its Focal Point, of events that may be a PHEIC under the instrument.
05 Response
- 08Public health responseStep · National DeskArticle 13 requires each State Party to build capacity to respond promptly and effectively to public health risks and emergencies.
- 09After-action reviewStepThe IHR monitoring and evaluation framework includes voluntary after action reviews, next to the Joint External Evaluation (JEE).
Neutral outline of a published external standard or method, from its issuing body. Not a record of operation. Nexus does not perform, certify or approve any step shown. A gate or decision belongs to the party the source names. Annex 2 is applied by the State Party, not by Nexus. The text read is the third edition (2016).
06In systemic risk work
Transmission meets supply chains and behaviour.
Epidemic models are among the most visible models in public decisions, and their outputs are used far outside epidemiology: school closures, supply-chain planning, economic support. Systemic use needs explicit links to behaviour, health-system capacity and economic activity, each of which feeds back on transmission.
- State whether reproduction numbers are estimated or assumed, and for which period.
- Separate reporting delays and testing changes from real changes in incidence.
- Represent health-system capacity as a constraint, not an output.
- Applications on Health Nexus.
07Applied in
Platforms that apply this method.
08Stewardship
Who maintains this page.
Health Nexus stewards epidemiology and public health science: it keeps this description current and reviews how the method is applied across the platforms.
09Sources
Where this page’s references lead.
The bodies and documents this page is read against. Status and editions change; each link goes to the issuing body.
10Questions
Questions and answers.
Why does one institution host every method page?
GCRI hosts the STEM Commons so that each method has one canonical description. Platforms link to it rather than repeat it, which keeps definitions consistent.
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Write to the integrity concern form with the passage and the reason.
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