Epi Weeks Overview
Epidemiological weeks are standardized weekly intervals used globally for disease surveillance, outbreak detection, and public health reporting.
Purpose
Epidemiological weeks (epi weeks) provide a uniform temporal framework that enables consistent comparison of disease incidence data across time periods and geographic regions.
Public health authorities worldwide use epidemiological weeks to aggregate surveillance data, monitor outbreak progression, identify seasonal trends, and conduct year-over-year comparisons.
Why Not Calendar Weeks?
Calendar week definitions vary internationally, with different starting days and week numbering conventions. Some start the week on Sunday, others on Monday. The first week of the year is also defined differently.
Epidemiological weeks establish the temporal consistency essential for valid surveillance data comparison across regions and time periods.
Two Main Systems
Two primary systems are used for epidemiological week numbering:
- CDC Week System: Based on the MMWR methodology used by the US CDC. Weeks start on Sunday.
- ISO Week System: Based on the ISO 8601 standard used by WHO. Weeks start on Monday.
Common Use Cases
- Influenza surveillance and seasonal flu reporting
- Respiratory disease and COVID-19 surveillance
- Outbreak detection, investigation, and response coordination
- Vaccine coverage and effectiveness studies
- Inter-annual disease incidence comparisons
- Epidemiological research and peer-reviewed publications