United States COVID-19 County Level of Community Transmission Historical Changes

<b>Announcement</b>
Beginning <b>October 20, 2022</b>, CDC will report and publish aggregate case and death data from jurisdictional and state partners on a weekly basis rather than daily. As a result, community transmission levels data reported on data.cdc.gov will be updated weekly on <b>Thursdays</b>, typically by <b>8 PM ET</b>, instead of daily. 

This public use dataset has 7 data elements reflecting historical data for community transmission levels for all available counties. This dataset contains historical data for the county level of community transmission and includes updated data submitted by states and jurisdictions.  Each day, the dataset is appended to contain the most recent day's data. This dataset includes data from January 1, 2021.  Transmission level is set to low, moderate, substantial, or high using the calculation rules below.

Currently, CDC provides the public with two versions of COVID-19 county-level community transmission level data: this dataset with the levels for each county from January 1, 2021 (<a href="https://data.cdc.gov/Public-Health-Surveillance/United-States-COVID-19-County-Level-of-Community-T/nra9-vzzn">Historical Changes dataset</a>) and a dataset with the levels as originally posted (<a href="https://data.cdc.gov/Public-Health-Surveillance/United-States-COVID-19-County-Level-of-Community-T/8396-v7yb">Originally Posted dataset</a>), updated daily with the most recent day’s data.

<b>Methods for calculating county level of community transmission indicator</b>
The County Level of Community Transmission indicator uses two metrics: (1) total new COVID-19 cases per 100,000 persons in the last 7 days and (2) percentage of positive SARS-CoV-2 diagnostic nucleic acid amplification tests (NAAT) in the last 7 days. For each of these metrics, CDC classifies transmission values as low, moderate, substantial, or high (below and <a href="https://www.cdc.gov/mmwr/volumes/70/wr/mm7030e2.htm?s_cid=mm7030e2_w#T1_down">here</a>). If the values for each of these two metrics differ (e.g., one indicates moderate and the other low), then the higher of the two should be used for decision-making. 

<b>CDC core metrics of and thresholds for community transmission levels of SARS-CoV-2</b>

<b>Total New Case Rate Metric</b>: "New cases per 100,000 persons in the past 7 days" is calculated by adding the number of new cases in the county (or other administrative level) in the last 7 days divided by the population in the county (or other administrative level) and multiplying by 100,000. "New cases per 100,000 persons in the past 7 days" is considered to have transmission level of Low (0-9.99); Moderate (10.00-49.99); Substantial (50.00-99.99); and High (greater than or equal to 100.00).

<b>Test Percent Positivity Metric</b>: "Percentage of positive NAAT in the past 7 days" is calculated by dividing the number of positive tests in the county (or other administrative level) during the last 7 days by the total number of tests resulted over the last 7 days. "Percentage of positive NAAT in the past 7 days" is considered to have transmission level of Low (less than 5.00); Moderate (5.00-7.99); Substantial (8.00-9.99); and High (greater than or equal to 10.00).

If the two metrics suggest different transmission levels, the higher level is selected. If one metric is missing, the other metric is used for the indicator.  

Transmission categories include: 

Low Transmission Threshold: Counties with fewer than 10 total cases per 100,000 population in the past 7 days, and a NAAT percent test positivity in the past 7 days below 5%; 

Moderate Transmission Threshold: Counties with 10-49 total cases per 100,000 population in the past 7 days or a NAAT test percent positivity in the past 7 days of 5.0-7.99%; 

Substantial Transmission Threshold: Counties with 50-99 total cases per 100,000 population in the past 7 days or a NAAT test percent positivity in the past 7 days of 8.0-9.99%; 

High Transmission Threshold: Counties with 100

Tags: cases, community-transmission, coronavirus, county, covid-19, laboratory
Organization: U.S. Department of Health & Human Services