Unifying Concepts

Case Definition for Coronavirus Disease 2019 (COVID-19)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly identified pathogen and it is assumed there is no pre-existing human immunity to the virus. Initial seroconversion, including neutralizing antibodies, has been documented and there is some evidence that immunity to SARS-CoV-2 re-challenge during early convalescence is likely.

Clinical Criteria
In the absence of a more likely diagnosis:

  • At least two of the following symptoms:
    • fever (measured or subjective),
    • chills,
    • rigors,
    • myalgia,
    • headache,
    • sore throat,
    • nausea or vomiting,
    • diarrhea,
    • fatigue,
    • congestion or runny nose


  • Any one of the following symptoms:
    • cough,
    • shortness of breath,
    • difficulty breathing,
    • new olfactory disorder,
    • new taste disorder


  • Severe respiratory illness with at least one of the following:
    • Clinical or radiographic evidence of pneumonia,
    • Acute respiratory distress syndrome (ARDS).

Laboratory Criteria
Laboratory evidence using a method approved or authorized by the FDA4 or designated authority:

Confirmatory* laboratory evidence:

  • Detection of severe acute respiratory syndrome coronavirus 2 ribonucleic acid (SARS-CoV-2 RNA) in a clinical or autopsy specimen using a molecular amplification test

Presumptive* laboratory evidence:

  • Detection of SARS-CoV-2 by antigen test in a respiratory specimen

Supportive* laboratory evidence:

  • Detection of specific antibody in serum, plasma, or whole blood
  • Detection of specific antigen by immunocytochemistry in an autopsy specimen

*The terms confirmatory, presumptive, and supportive are categorical labels used here to standardize case classifications for public health surveillance. The terms should not be used to interpret the utility or validity of any laboratory test methodology.

Epidemiologic Linkage
One or more of the following exposures in the prior 14 days:

  • Close contact** with a confirmed or probable case of COVID-19 disease;
  • Member of a risk cohort as defined by public health authorities during an outbreak.

**Close contact is generally defined as being within 6 feet (1,8 m) for at least 15 minutes. However, it depends on the exposure level and setting; for example, in the setting of an aerosol-generating procedure in healthcare settings without proper personal protective equipment (PPE), this may be defined as any duration. Data are insufficient to precisely define the duration of exposure that constitutes prolonged exposure and thus a close contact.

Criteria to Distinguish a New Case from an Existing Case
A repeat positive test for SARS-CoV-2 RNA using a molecular amplification detection test within 3 months of the initial report should not be enumerated as a new case for surveillance purposes. To date, there has been minimal evidence of re-infection among persons with a prior confirmed COVID-19 infection and growing evidence that repeat positive RNA tests do not correlate with active infection when viral culture is performed. Similarly the experience with other coronaviruses is that reinfection is rare within the first year. NOTE: The time period of 3 months will be extended further when more data becomes available to show risk of reinfection remains low within one year of the initial report.

Case Classification


  • Meets supportive laboratory evidence*** with no prior history of being a confirmed or probable case.

*** For suspect cases (positive serology only), jurisdictions may opt to place them in a registry for other epidemiological analyses or investigate to determine probable or confirmed status.


  • Meets clinical criteria AND epidemiologic linkage with no confirmatory laboratory testing performed for SARS-CoV-2.
  • Meets presumptive laboratory evidence.
  • Meets vital records criteria with no confirmatory laboratory evidence for SARS-CoV-2.

Meets confirmatory laboratory evidence.

Other Criteria
Vital Records Criteria



  1. Coronavirus Disease 2019 (COVID-19) 2020 Interim Case Definition, Approved August 5, 2020 [CDC]
  2. Garcia M, Lipskiy N, Tyson J, Watkins R, Esser ES, Kinley T. Centers for Disease Control and Prevention 2019 novel coronavirus disease (COVID-19) information management: addressing national health-care and public health needs for standardized data definitions and codified vocabulary for data exchange. J Am Med Inform Assoc. 2020 Jul 1;27(9):1476-1487. [Medline]


Created Oct 29, 2020.

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