The U.S. Centers for Disease Control and Prevention (CDC) uses two data sources for information on COVID cases: aggregate count data and in-line level (patient-level data). According to CDC, the differences between these are as follows:
- Aggregate count data: high-level information about case and death totals.
- Line-level (patient-level) data: specific information for each case, including: patient demographics, signs and symptoms of illness, underlying health conditions, characteristics of hospitalizations,clinical outcomes, and exposures.
Line-level data is primarily from state health departments, like the Virginia Department of Health. Collecting line-level data is substantially more involved and time-consuming than aggregate count reporting.
In October 2022, CDC changed the cadence of line-level reporting from daily to weekly. This was done to "allow for additional reporting flexibility, reduce the reporting burden on states and jurisdictions, and maximize surveillance resources."