Companion Guide: NSSP ED Data on Respiratory Illness

Introduction

The National Syndromic Surveillance Program (NSSP) is a collaboration among CDC, local and state health departments, with private sector partners. Together, these partners collect, share, and analyze automated electronic healthcare data in near-real time.

The national data include emergency departments in all 50 states, the District of Columbia, and Guam. View the coverage map here.

Inclusion

Diagnostic codes and clinical terms were used to create definitions for diagnosed COVID-19, influenza, and RSV. Jurisdiction-level data are not shown for Missouri because the proportion of records with a discharge diagnosis is low. Jurisdiction-level data are not shown for New Hampshire, South Dakota, and Washington to ensure data use and other sharing agreements are appropriately addressed prior to public release. Guam is not shown due to small counts.

Emergency department visits were assigned to the Morbidity and Mortality Weekly Report (MMWR) week they occurred; MMWR weeks begin on Sunday and end on the following Saturday. MMWR week #1 of an MMWR year is the first week of the year that has at least four days in the calendar year.

Considerations for interpretation of data

Variability in testing practices for different viruses and in different age groups may lead to under-ascertainment of respiratory infections in electronic healthcare data, including emergency department visits. Patients who are less likely to be tested are less likely to be included. These data are based on electronic diagnostic codes transmitted automatically in near real-time, and hospital practices for assigning these codes can vary. These data are dynamic and update as codes are added and changed.

The weekly percent of emergency department visits with COVID-19 diagnosis on this site are not designed to match the percentages shown on the CDC COVID Data Tracker. Metrics will differ across websites due to factors such as updates on different days of the week or different calculations, such as presentation of a 7-day moving average on daily data rather than weekly totals. Data will also differ from state websites due to different update schedules, calculations, or definitions. These data are not a random sample and are not intended to capture data from every hospital. While these data are not designed to be randomly sampled or comprehensive, they provide a useful overall indicator of trends in emergency department use.

How percent of visits is calculated

For data that are presented as a percentage, each respiratory illness is presented as a percent of all emergency department visits by age group. For example, the COVID-19 data show emergency department visits for children ages 5-11 with diagnosed COVID-19 as a fraction of all emergency department visits for children ages 5-11.

Definitions

The following discharge diagnoses (DD) and clinical terms are included: International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM), the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM), and Systematized Nomenclature of Medicine – Clinical Terms (SNOMED CT). Please note that conditions can be defined in different ways in electronic healthcare data, and some jurisdictions may use different definitions. Short codes listed capture all codes underneath (J09 captures J09.X1-J09.X9).

COVID-19

Definition name in the NSSP Electronic Surveillance System for the Early Notification of Community-Based Epidemics (ESSENCE) system: CDC COVID-Specific DD v1

Influenza

Definition name in the NSSP ESSENCE system: CDC Influenza DD v1

RSV

Definition name in the NSSP ESSENCE system: CDC Respiratory Syncytial Virus DD v1