COVIDcast Epidata API

This is the documentation for accessing Delphi’s COVID-19 indicators via the covidcast endpoint of Delphi’s epidemiological data API. This API provides data on the spread and impact of the COVID-19 pandemic across the United States, most of which is available at the county level and updated daily. This data powers our public COVIDcast map which includes testing, cases, and death data, as well as unique healthcare and survey data Delphi acquires through its partners. The API allows users to select specific signals and download data for selected geographical areas—counties, states, metropolitan statistical areas, and other divisions.

Table of contents

1. COVIDcast Epidata API
   1. Licensing
   2. Accessing the Data
   3. Data Sources and Signals
   4. Constructing API Queries
      1. Query Parameters
         1. Required
         2. Optional
      2. Response
      3. Alternative Response Formats
         1. JSON List Response
         2. CSV File Response
         3. JSON New Lines Response
      4. Limit Returned Fields
   5. Example URLs
      1. Facebook Survey CLI on 2020-04-06 to 2010-04-10 (county 06001)
      2. Facebook Survey CLI on 2020-04-06 (all counties)

Licensing

Like all other Delphi Epidata datasets, our COVIDcast data is freely available to the public. However, our COVID-19 indicators include data from many different sources, with data licensing handled separately for each source. For a summary of the licenses used and a list of the indicators each license applies to, we suggest users visit our COVIDcast licensing page. Licensing information is also summarized on each indicator’s details page. We encourage academic users to cite the data if they use it in any publications. Our data ingestion code and API server code is open-source, and contributions are welcome. Further documentation on Delphi’s APIs is available in the API overview.

Accessing the Data

Our COVIDcast site provides an interactive visualization of a select set of the data signals available in the COVIDcast API, and provides a data export feature to download any data range as a CSV file.

Several API clients are available for common programming languages, so you do not need to construct API calls yourself to obtain COVIDcast data. Once you install the appropriate client for your programming language, accessing data is as easy as, in R:

library(covidcast)

data <- covidcast_signal("fb-survey", "smoothed_cli", start_day = "2020-05-01",
                         end_day = "2020-05-07")

or, in Python:

import covidcast
from datetime import date

data = covidcast.signal("fb-survey", "smoothed_cli", date(2020, 5, 1), date(2020, 5, 7),
                        "county")

The API clients have extensive documentation providing further examples.

Alternately, to construct URLs and parse responses to access data manually, see below for details.

Data Sources and Signals

The API provides multiple data sources, each with several signals. Each source represents one provider of data, such as a medical testing provider or a symptom survey, and each signal represents one quantity computed from data provided by that source. Our sources provide detailed data about COVID-related topics, including confirmed cases, symptom-related search queries, hospitalizations, outpatient doctor’s visits, and other sources. Many of these are publicly available only through the COVIDcast API.

The signals documentation describes all available sources and signals.

Constructing API Queries

The COVIDcast API is based on HTTP GET queries and returns data in JSON form. The base URL is https://api.delphi.cmu.edu/epidata/covidcast/.

See this documentation for details on specifying epiweeks, dates, and lists.

Query Parameters

Required

The current set of signals available for each data source is returned by the covidcast_meta endpoint.

Optional

Estimates for a specific time_value and geo_value are sometimes updated after they are first published. Many of our data sources issue corrections or backfill estimates as data arrives; see the documentation for each source for details.

The default API behavior is to return the most recently issued value for each time_value selected.

We also provide access to previous versions of data using the optional query parameters below.

Use cases:

• To pretend like you queried the API on June 1, such that the returned results do not include any updates that became available after June 1, use as_of=20200601.
• To retrieve only data that was published or updated on June 1, and exclude records whose most recent update occurred earlier than June 1, use issues=20200601.
• To retrieve all data that was published between May 1 and June 1, and exclude records whose most recent update occurred earlier than May 1, use issues=20200501-20200601. The results will include all matching issues for each time_value, not just the most recent.
• To retrieve only data that was published or updated exactly 3 days after the underlying events occurred, use lag=3.

You should specify only one of these three parameters in any given query.

Note: Each issue in the versioning system contains only the records added or updated during that time unit; we exclude records whose values remain the same as a previous issue. If you have a research problem that would require knowing when we last confirmed an unchanged value, please get in touch.

Response

Note: result code 2, “too many results”, means that the number of results you requested was greater than the API’s maximum results limit. Results will be returned, but not all of the results you requested. API clients should check the results code and consider breaking up requests for e.g. large time intervals into multiple API calls.

Alternative Response Formats

In addition to the default EpiData Response format, users can customize the response format using the format= parameter.

JSON List Response

When setting the format parameter to format=json, it will return a plain list of the epidata response objects without the result and message wrapper. The status of the query is returned via HTTP status codes. For example, a status code of 200 means the query succeeded, while 400 indicates that the query has a missing, misspelled, or otherwise invalid parameter. For all status codes != 200, the returned JSON includes details about what part of the query couldn’t be interpreted.

CSV File Response

When setting the format parameter to format=csv, it will return a CSV file with same columns as the response objects. HTTP status codes are used to communicate success/failure, similar to format=json.

JSON New Lines Response

When setting the format parameter to format=jsonl, it will return each row as an JSON file separated by a single new line character \n. This format is useful for incremental streaming of the results. Similar to the JSON list response status codes are used.

Limit Returned Fields

The fields parameter can be used to limit which fields are included in each returned row. This is useful in web applications to reduce the amount of data transmitted. The fields parameter supports two syntaxes: allow and deny. Using allowlist syntax, only the listed fields will be returned. For example, fields=geo_value,value will drop all fields from the returned data except for geo_value and value. To use denylist syntax instead, prefix each field name with a dash (-) to exclude it from the results. For example, fields=-direction will include all fields in the returned data except for the direction field.

Example URLs

Facebook Survey CLI on 2020-04-06 to 2010-04-10 (county 06001)

https://api.delphi.cmu.edu/epidata/covidcast/?data_source=fb-survey&signal=smoothed_cli&time_type=day&geo_type=county&time_values=20200406-20200410&geo_value=06001

{
  "result": 1,
  "epidata": [
    {
      "geo_value": "06001",
      "time_value": 20200407,
      "direction": null,
      "value": 1.1293550689064,
      "stderr": 0.53185454111042,
      "sample_size": 281.0245
    },
    ...
  ],
  "message": "success"
}

Facebook Survey CLI on 2020-04-06 (all counties)

https://api.delphi.cmu.edu/epidata/covidcast/?data_source=fb-survey&signal=smoothed_cli&time_type=day&geo_type=county&time_values=20200406&geo_value=*

{
  "result": 1,
  "epidata": [
    {
      "geo_value": "01000",
      "time_value": 20200406,
      "direction": null,
      "value": 1.1693378,
      "stderr": 0.1909232,
      "sample_size": 1451.0327
    },
    ...
  ],
  "message": "success"
}

Table of contents

• API Clients
• COVIDcast Data Licensing
• Data Sources and Signals
• Signal Changelog
• Geographic Coding
• Date Coding and Revisions
• NaN Missing Codes
• Metadata
• Inactive Signals