NSSP ED Trajectories: Weekly Respiratory Illness Trends by U.S. State and County

U.S. emergency department visit data from the National Syndromic Surveillance Program tracks weekly trends for COVID-19, influenza, and RSV. The dataset provides the percentage of visits for each pathogen by state and Health Service Area, along with classifications of trends as increasing, decreasing, or stable. It is updated weekly by the CDC.

Use Cases

• Model weekly pathogen prevalence using percent_visits_covid, percent_visits_influenza, and percent_visits_rsv across different geographies.
• Analyze trend direction changes over time using ed_trends_covid, ed_trends_influenza, and ed_trends_rsv columns.
• Compare smoothed and raw visit percentages via percent_visits_smoothed_combined and percent_visits_combined for signal analysis.
• Aggregate or filter data by geographic hierarchy using state, county, fips, and hsa columns.
• Join with other demographic datasets using the fips or hsa_nci_id columns for county-level analysis.

Strengths

• Includes trend classifications (increasing/decreasing/stable) derived from statistical modeling of time-series data.
• Provides data at multiple geographic levels: state, Health Service Area (HSA), and county.
• Covers three major respiratory pathogens (COVID-19, influenza, RSV) and a combined measure.
• Updated weekly on Fridays, as of 2026-04-03.

Limitations

• Row count and total dataset size are unknown, which may limit suitability assessment.
• Data for some regions may be classified as 'sparse' if many weeks have 0% visits, preventing trend calculation.
• License and author information are not provided in the available metadata.

Provenance

Source

data.cdc.gov, via the National Syndromic Surveillance Program (NSSP).

Collection Method

Aggregated from emergency department visit data submitted by participating healthcare facilities.

Time Range

Weekly data; specific start date not provided.

Freshness

Updated once per week on Fridays.

Geography

United States, by state and sub-state Health Service Areas (HSAs) comprising one or more counties.