Case Definition issues
This page collects observations, interpretations, and consequences for action about the case definition of SARS-CoV2 in general. Please observe the structure of the page, when you add your content. Please use references where possible. Remember to find the relevant page. For example, if your observation is about transmission routes, please use that page, instead of posting your content here.
- 1 What is already known
- 2 Implementing case definition changes (2 March 2020)
- 3 National COVID-19 Case Definitions and/or Criteria for Testing
- 4 References
What is already known
WHO Case Definition (creation date: 27 February 2020, publishing date: 2 March 2020)
A suspected case is:
A. a patient with acute respiratory illness (that is, fever and at least one sign or symptom of respiratory disease, for example, cough or shortness of breath) AND with no other etiology that fully explains the clinical presentation AND a history of travel to or residence in a country, area or territory that has reported local transmission of COVID-19 disease during the 14 days prior to symptom onset (for updated reporting, see the situation reports at https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports/ ;
B. a patient with any acute respiratory illness AND who has been a contact of a confirmed or probable case of COVID-19 disease during the 14 days prior to the onset of symptoms (see the definition of contact below);
C. a patient with severe acute respiratory infection (that is, fever and at least one sign or symptom of respiratory disease, for example, cough or shortness breath) AND who requires hospitalization AND who has no other etiology that fully explains the clinical presentation.
ECDC Case Definition (creation date: unknown, publishing date: 2 March 2020)
Laboratory testing for COVID-19 should be performed for suspected cases according to the following criteria, based on the updated WHO case definition:
1) a patient with acute respiratory tract infection (sudden onset of at least one of the following: cough, fever, shortness of breath) AND with no other aetiology that fully explains the clinical presentation AND with a history of travel or residence in a country/area reporting local or community transmission* during the 14 days prior to symptom onset;
2) a patient with any acute respiratory illness AND having been in close contact with a confirmed or probable COVID-19 case in the last 14 days prior to onset of symptoms;
3) A patient with severe acute respiratory infection (fever and at least one sign/symptom of respiratory disease (e.g., cough, fever, shortness breath)) AND requiring hospitalisation (SARI) AND with no other aetiology that fully explains the clinical presentation.
- according to WHO classification, see respective daily updated Coronavirus disease (COVID-2019) situation reports at https://www.who.int/emergencies/diseases/novel-coronavirus-2019/situation-reports/
(1) The two case definitions are similiar, but not the same. Imagine that you have to develop a checklist for physicians to facilitate their case assessment process. For WHO, an acute respiratory infection (ARI) means "fever and at least one sign or symptom of respiratory disease for example, cough or shortness breath)", for ECDC, an ARI means "sudden onset of at least one of the following: cough, fever, shortness of breath". So: What does your ARI checklist look like?
(2) Given that the spread of SARS-CoV-2 has resulted in a massive public health emergency worldwide, it is not self-explanatory why physicians are recommended to exclude other causes/pathogens first, according to WHO and ECDC (see "with no other aetiology that fully explains the clinical presentation" clause in the case definitions).
Implementing case definition changes (2 March 2020)
WHO (and ECDC) published their new recommendation on COVID case definition on March 2: this contained a significant shift from the previous approach.
- Countries were not aware that this new WHO/ECDC approach was coming out on March 2.
- The new approach created anxiety. Experts were surprised that WHO did not distinguish between countries with "local transmission". De facto, the majority of returning travelers now came from Corona-Risk areas, regardless of the extent of transmission.
- The new approach had a significant impact on testing demand, generating discussions on how to deal with that. In addition, it impacted on case identification among the hospitalized SARI cases, which might have received less attention due to focus on the widely extended travel criteria. Much time was spent (and lost?) on discussing priorities for testing.
- Some countries were seeing in their epidemiological data that the case definition did not work well before March 2. They were confused on whether they should wait for the change definition at a European level or proceed with a change by their own. This delay led to critisism from the public and the Media towards the public health authorities.
Analysis and interpretation
- This led to some countries still having no updated policy several days or even two weeks after the new case definitions were published, and as a consequence, most of the medical staff was still focussing on suspected cases coming from high-risk areas with obvious, widespread community transmission of SARS-CoV-2 (such as Italy, China, Iran, South-Korea) or on suspected cases having had contact with a confirmed case only. As a consequence, many new COVID-19 cases could have remained undetected and unreported.
- Some experts strongly disagree with WHO/ECDC about the need to exclude other etiology first. The recommendation is probably aimed to decrease the need for COVID-19 testing, but the fact that this leads to a significant delay in the COVID-19 diagnosis (and thus increased exposure of healthcare workers to undetected COVID-19) some experts find hard to accept.
- The above analysis reflects the situation that had arisen shortly after 2 March. Circumstances and case numbers have rapidly changed since then in many countries, furthermore extremely strict travel restrictions have been implemented by many governments rendering the travel criteria less and less relevant.
Consequences for and considerations about action
- Countries should be prepared to rapidly shift gear when international case guidelines change. During pandemics, it is unrealistic to expect that coordinating organizations such as WHO and ECDC can predict when they will change guidelines, so one cannot expect timetables for this. However, since both WHO and ECDC have formally nominated contact points in national public health bodies, it is still sensible and possible to inform countries at least one or two days in advance about major changes planned. Note that the WHO case definition was created on 27 February and published on 2 March only.
- Communication channels from national public health bodies to health care professionals should ideally allow for such rapid changes, and a platform of rapid exchange of information and advice would be beneficial. However, it is unrealistic to expect that national laboratory capacity, health care staff (primary, secondary, tertiary) and public health authorities have the chance to follow and implement changes immediately.
- Health care providers on their term should be prepared to receive rapidly changing guidelines during international infectious disease crises. What is considered a constant among all large pandemics, is that gaps in knowledge are rapidly filled; therefore new insights have to be translated to an improvement of prevention and control in a timely and efficient way. However, when health care providers are increasingly overwhelmed with the management of new suspected and confirmed COVID-19 cases, the focus may inevitably shift to imminent treatment efforts.
- One of the possible ways for countries to prepare for this is to have regular simulation exercises that take these issues into account. It is particularly important for countries to design their own national simulation exercises as health care systems (including infrastructure, staffing, organisation of laboratory services and other relevant factors), health care seeking behaviour, and cultural determinants differ significantly.
National COVID-19 Case Definitions and/or Criteria for Testing
France See "Definition de cas"
Germany See "Falldefinition Coronavirus Disease 2019"
Sweden See "Falldefinitioner vid anmälan enligt smittskyddslagen av infektion med covid-19"
Greece See "Λοίμωξη από νέος κορωνοϊό Covid-19 – Κριτήρια για εργαστηριακό έλεγχο"