CDC reports aggregate counts of COVID-19 cases and death numbers daily online. Data on the COVID-19 website and CDC’s COVID Data Tracker are based on these most recent numbers reported by states, territories, and other jurisdictions. This data set of “United States COVID-19 Cases and Deaths by State over Time” combines this information. However, data are dependent on jurisdictions’ timely and accurate reporting.
Separately, CDC also regularly reports provisional death certificate data from the National Vital Statistics System (NVSS) on data.cdc.gov. Details are described on the NCHS website. Reporting the number of deaths by using death certificates ultimately provides more complete information but is a longer process; therefore, these numbers will be less than the death counts on the COVID-19 website.
Accuracy of Data
CDC tracks COVID-19 illnesses, hospitalizations, and deaths to track trends, detect outbreaks, and monitor whether public health measures are working. However, counting exact numbers of COVID-19 cases is not possible. COVID-19 can cause mild illness, symptoms might not appear immediately, there are delays in reporting and testing, not everyone who is infected gets tested or seeks medical care, and there are differences in how completely states and territories report their cases.
COVID-19 is one of about 120 diseases or conditions health departments voluntarily report to CDC. State, local, and territorial public health departments verify and report cases to CDC. When there are differences between numbers of cases reported by CDC versus by health departments, data reported by health departments should be considered the most up to date. Health departments may update case data over time when they receive more complete and accurate information. The number of new cases reported each day fluctuates. There is generally less reporting on the weekends and holidays.
CDC reports death data on three other sections of the website: U.S. Cases & Deaths, COVID Data Tracker, and NCHS Provisional Death Counts. The U.S. Cases and Deaths webpages and COVID Data Tracker get their information from the same source (total case counts); however, NCHS Death Counts are based on death certificates that use information reported by physicians, medical examiners, or coroners in the cause-of-death section of each certificate. Data from each of these pages are considered provisional (not complete and pending verification) and are therefore subject to change. Counts from previous weeks are continually revised as more records are received and processed. Because not all jurisdictions report counts daily, counts may increase at different intervals.
Confirmed & Probable Counts
As of April 14, 2020, CDC case counts and death counts include both confirmed and probable cases and deaths. This change was made to reflect an interim COVID-19 position statement issued by the Council for State and Territorial Epidemiologists on April 5, 2020. The position statement included a case definition and made COVID-19 a nationally notifiable disease. Nationally notifiable disease cases are voluntarily reported to CDC by jurisdictions. Confirmed and probable case definition criteria are described here:
https://wwwn.cdc.gov/nndss/conditions/coronavirus-disease-2019-covid-19/case-definition/2020/. Not all jurisdictions report probable cases and deaths to CDC. When not available to CDC, it is noted as N/A. Please note that jurisdiction
The COVID-19 case surveillance system database includes patient-level data reported to U.S. states and autonomous reporting entities, including New York City and the District of Columbia (D.C.), as well as U.S. territories and states. On April 5, 2020, COVID-19 was added to the Nationally Notifiable Condition List and classified as “immediately notifiable, urgent (within 24 hours)” by a Council of State and Territorial Epidemiologists (CSTE) Interim Position Statement (Interim-20-ID-01). The statement also recommended that all states and territories enact laws to make COVID-19 reportable in their jurisdiction, and that jurisdictions conducting surveillance should submit case notifications to CDC. COVID-19 case surveillance data are collected and reported voluntarily to CDC’s COVID-19 Response.
These deidentified data include demographic characteristics, exposure history, disease severity indicators and outcomes, clinical data, laboratory diagnostic test results, and comorbidities. All data elements can be found on the COVID-19 case report form located at www.cdc.gov/coronavirus/2019-ncov/downloads/pui-form.pdf.
The Case Surveillance Task Force and Surveillance Review and Response Group (SRRG) within CDC’s COVID-19 Response provide stewardship for datasets that support the public health community’s access to COVID-19 data while protecting patient privacy.
COVID-19 case reports have been routinely submitted using standardized case reporting forms. On April 5, 2020, CSTE released an Interim Position Statement with national surveillance case definitions for COVID-19 included. Current versions of these case definitions are available here: https://wwwn.cdc.gov/nndss/conditions/coronavirus-disease-2019-covid-19/. All cases reported on or after were requested to be reported by public health departments to CDC using the standardized case definitions for lab-confirmed or probable cases. On May 5, 2020, the standardized case reporting form was revised. Implementation of case reporting using this new form is ongoing among U.S. states and territories.
The COVID-19 case surveillance data are dynamic; case reports can be modified at any time by the reporting jurisdiction as new information becomes available (i.e., data are subject to change). Furthermore, reporting jurisdictions may report cases late. Version updates to the detailed and limited datasets will be available for request once a month.
The datasets will include all cases with an initial report date of case to CDC at least 14 days prior to the creation of the previously updated datasets. This 14 day lag will allow case reporting to be stabilized and ensure that time-dependent outcome data, including death, are accurately captured.
CDC’s Case Surveillance Task Force routinely performs data quality assurance procedures (i.e., ongoing corrections and logic checks to address data errors). To date, the following data cleaning steps have been implemented:
Questions that have been left unanswered (blank) on the case report form are re-classified to a Missing value, if applicable to the question. For example, in the question “Was the patient hospitalized?”, where the possible answer choices include “Yes”, “No”, or “Unknown”, the missing value is re-coded to Missing if the respondent did not answer the question.
Logic checks are performed for date data. If an illogical date has been provided, CDC reviews the data with the reporting jurisdiction. For example, if a symptom onset date that is in the future is reported to CDC, this value is set to null until the reporting jurisdiction updates this information appropriately.
The initial report date of the case to CDC is intended to be completed by the reporting jurisdiction when data are submitted. If blank, this variable is completed using the date