Case definitions for COVID-19 surveillance – 16 December 2020

Updated Definition cases for COVID-19 Surveillance

 

1. Case definitions 

Case and contact definitions are based on the current available information and are regularly revised as new information accumulates. Countries may need to adapt case definitions depending on their local epidemiological situation and other factors. All countries are encouraged to publish definitions used online and in regular situation reports, and to document periodic updates to definitions which may affect the interpretation of surveillance data. 

Suspected case of SARS-CoV-2 infection (three options, A through C):

A. A person who meets the clinical AND epidemiological criteria:

Clinical criteria:

  1. Acute onset of fever AND cough; or 
     
  2. Acute onset of ANY THREE OR MORE of the following signs or symptoms: fever, cough, general weakness/fatigue,1 headache, myalgia, sore throat, coryza, dyspnoea, anorexia/nausea/vomiting, diarrhea, altered mental status.

AND

Epidemiological criteria:

  1. Residing or working in a setting with high risk of transmission of the virus: for example, closed residential settings and humanitarian settings, such as camp and camp-like settings for displaced persons, any time within the 14 days before symptom onset; or 
     
  2. Residing in or travel to an area with community transmission anytime within the 14 days before symptom onset; or 
     
  3. Working in health setting, including within health facilities and within households, anytime within the 14 days before symptom onset.

 

B. A patient with severe acute respiratory illness (SARI: acute respiratory infection with history of fever or measured fever of ≥ 38 C°; and cough; with onset within the last 10 days; and who requires hospitalization).

C. An asymptomatic person not meeting epidemiologic criteria with a positive SARS-CoV-2 antigen-detecting rapid diagnostic test (Ag-RDT).2

Probable case of SARS-CoV-2 infection (four options, A through D):

  1. A patient who meets clinical criteria above AND is a contact of a probable or confirmed case or is linked to a COVID-19 cluster.3
     
  2. A suspected case (described above) with chest imaging showing findings suggestive of COVID-19 disease.4
     
  3. A person with recent onset of anosmia (loss of smell) or ageusia (loss of taste) in the absence of any other identified cause.
     
  4. Death, not otherwise explained, in an adult with respiratory distress preceding death AND who was a contact of a probable or confirmed case or linked to a COVID-19 cluster 3

Confirmed case of SARS-CoV-2 infection (three options, A through C):

  1. A person with a positive Nucleic Acid Amplification Test (NAAT)
     
  2. A person with a positive SARS-CoV-2 Ag-RDT AND meeting either the probable case definition or suspected criteria A OR B
     
  3. An asymptomatic person with a positive SARS-CoV-2 Ag-RDT AND who is a contact of a probable or confirmed case. 
Note: Clinical and public health judgment should be used to determine the need for further investigation in patients who do not strictly meet the clinical or epidemiological criteria. Surveillance case definitions should not be used as the sole basis for guiding clinical management.

2. Definition of a contact

A contact is a person who has experienced any one of the following exposures during the 2 days before and the 14 days after the onset of symptoms of a probable or confirmed case:

  1. face-to-face contact with a probable or confirmed case within 1 meter and for at least 15 minutes 
     
  2. direct physical contact with a probable or confirmed case 
     
  3. direct care for a patient with probable or confirmed COVID-19 disease without the use of recommended personal protective equipment, or  
     
  4. other situations as indicated by local risk assessments, as outlined in table 1 in Contact tracing in the context of COVID19.

More information on contact ascertainment is available in Contact tracing in the context of COVID-19. 

Note: for confirmed asymptomatic cases, the period of contact is measured as the 2 days before through the 14 days after the date on which the sample that led to confirmation was taken. 

3. Definition of death due to COVID-19

A COVID-19 death is defined for surveillance purposes as a death resulting from a clinically compatible illness in a probable or confirmed COVID-19 case, unless there is a clear alternative cause of death that cannot be related to COVID-19 disease (e.g. trauma). There should be no period of complete recovery between the illness and death.


1Signs separated with slash (/) are to be counted as one sign.
2NAAT is required for confirmation, see Diagnostic testing for SARS-CoV-2
3A group of symptomatic individuals linked by time, geographic location and common exposures, containing at least one NAAT-confirmed case or at least two epidemiologically linked, symptomatic (meeting clinical criteria of Suspect case definition A or B) persons with positive Ag-RDTs (based on ≥97% specificity of test and desired >99.9% probability of at least one positive result being a true positive)
4Typical chest imaging findings suggestive of COVID-19 include the following (Manna 2020 [6]):
- chest radiography: hazy opacities, often rounded in morphology, with peripheral and lower lung distribution
- chest CT: multiple bilateral ground glass opacities, often rounded in morphology, with peripheral and lower lung distribution
- lung ultrasound: thickened pleural lines, B lines (multifocal, discrete, or confluent), consolidative patterns with or without air bronchograms