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+---
+title: NHSN ED Visits
+parent: Data Sources and Signals
+grand_parent: Main Endpoint (COVIDcast)
+nav_order: 1
+---
+# National Syndromic Surveillance Program Emergency Department Visits
+{: .no_toc}
+
+* **Source name:** `nhsn`
+* **Earliest issue available:** August 08, 2020
+* **Number of data revisions since 18 Nov 2024:** 0
+* **Date of last change:** Never
+* **Available for:** state, hhs, nation (see [geography coding docs](../covidcast_geography.md))
+* **Time type:** week (see [date format docs](../covidcast_times.md))
+* **License:** [Public Domain US Government](https://www.usa.gov/government-works)
+
+## Overview
+
+[The National Healthcare Safety Network (NHSN)](https://www.cdc.gov/nhsn/index.html) is an effort to track epidemiologically relevant conditions.
+This dataset represents preliminary weekly hospital respiratory data and metrics aggregated to national and state/territory levels reported to CDC’s National Health Safety Network (NHSN) beginning August 2020.
+Each signal below is derived from one of two following datasets:
+- Main: [Weekly Hospital Respiratory Data (HRD) Metrics by Jurisdiction, National Healthcare Safety Network (NHSN)](https://data.cdc.gov/Public-Health-Surveillance/Weekly-Hospital-Respiratory-Data-HRD-Metrics-by-Ju/ua7e-t2fy/about_data)
+- Preliminary: [Weekly Hospital Respiratory Data (HRD) Metrics by Jurisdiction, National Healthcare Safety Network (NHSN) (Preliminary)](https://data.cdc.gov/Public-Health-Surveillance/Weekly-Hospital-Respiratory-Data-HRD-Metrics-by-Ju/mpgq-jmmr/about_data). Signals derived from the preliminary dataset have suffix `_prelim` in their signal names.
+
+Both datasets started reporting data in late 2022. As of May 2024, NHSN received data from 78% of US EDs.
+
+| Signal                          | Description                                                                                                                                                                         |
+|---------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `confirmed_admissions_covid_ew`              | Total number of patients hospitalized with confirmed COVID-19 captured for the Wednesday of the reporting week **Earliest date available:** 2020-08-08                                                                                                     |
+| `confirmed_admissions_covid_ew_prelim`          | Total number of patients hospitalized with confirmed COVID-19 captured for the Wednesday of the reporting week preliminary data reported to NHSN for the previous reporting week (Sunday – Saturday). <br/> **Earliest date available:** 2020-08-08  |
+| `confirmed_admissions_flu_ew`           | Total number of patients hospitalized with confirmed influenza captured for the Wednesday of the reporting week  <br/> **Earliest date available:** 2020-08-08                                                                                       |
+| `confirmed_admissions_flu_ew_prelim`     | Total number of patients hospitalized with confirmed influenza captured for the Wednesday of the reporting week  preliminary data reported to NHSN for the previous reporting week (Sunday – Saturday).<br/> **Earliest date available:** 2020-08-08 |
+
+## Table of Contents
+{: .no_toc .text-delta}
+
+1. TOC
+{:toc}
+
+## Estimation
+
+The confirmed signal `confirmed_admissions_covid_ew` is the value of the `totalconfc19newadm`
+The confirmed signal `confirmed_admissions_flu_ew` is the value of the `totalconfflunewadm`
+
+
+### Geographic weighting
+As the original data is a percentage and raw case counts are not available, `hrr`,`msa`, and `hhs` values are computed from county-level data using a weighted mean. Each county is assigned a weight equal to its population in the last census (2020). Unreported counties are implicitly treated as having a weight of 0 or a value equal to the group mean.
+
+This weighting approach assumes that the number of ED visits is proportional to the overall population of a county, i.e. the per-capita ED visit rate is the same for all counties, which may not be the case (for example, denser counties may have easier access to EDs and thus higher rates of ED visits per capita).
+
+state-level data is **not** simply an average of the county-level data, but may contain facilities omitted at the regional level. For example, state-level values are available for California, even though no California county data is reported; see the [missingness section below](#missingness) for a list of such states.
+
+
+## Missingness
+
+Data for reporting dates through April 30, 2024 represent data reported during a previous mandated reporting period as specified by the HHS Secretary.
+Data for reporting dates May 1, 2024 – October 31, 2024 represent voluntarily reported data in the absence of a mandate. 
+Data for reporting dates beginning November 1, 2024 represent data reported during a current mandated reporting period.
+All data and metrics capturing information on respiratory syncytial virus (RSV) were voluntarily reported until November 1, 2024.
+
+
+## Lag and Backfill
+
+The weekly signal is primarily reported on Friday, adding data from the prior week.
+For example, on Friday, 2024-04-19, the source added new data from the week ending 2024-04-13.
+
+## Limitations
+
+
+## Source and Licensing
+
+This source is derived from the CDC's [Weekly Hospital Respiratory Data (HRD) Metrics by Jurisdiction, National Healthcare Safety Network (NHSN)](https://data.cdc.gov/Public-Health-Surveillance/Weekly-Hospital-Respiratory-Data-HRD-Metrics-by-Ju/ua7e-t2fy/about_data) and
+[Weekly Hospital Respiratory Data (HRD) Metrics by Jurisdiction, National Healthcare Safety Network (NHSN) (Preliminary)](https://data.cdc.gov/Public-Health-Surveillance/Weekly-Hospital-Respiratory-Data-HRD-Metrics-by-Ju/mpgq-jmmr/about_data).
+
+This data was originally published by the CDC, and is made available here as a convenience to the forecasting community under the terms of the original license, which is [U.S. Government Public Domain](https://www.usa.gov/government-copyright).