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.

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/novelcoronavirus-2019/situation-reports/);

OR

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);

OR

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;

OR

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;

OR

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/

Take note:

(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

Observations

• 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 informed in advance by WHO/ECDC that this was coming out. Some had just updated the national protocol and distribute it widely to hospitals and PH authorities, moments before receiving the updated approach from WHO.
  • This created much 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.
  • This 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. Much time was spent (and lost?) on discussing priorities for testing.

Analysis and interpretation

• This led to some countries still having no updated policy two weeks after the new case definitions were published, and as a consequence, most of the medical staff was still focussing on people coming from the original high-risk areas or contact with a confirmed case only; as a consequence, new COVID19 cases remain unreported.
• Some experts strongly disagree with WHO 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 public health experts find hard to digest.

Consequences for 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.
  • Communication channels from national public health bodies to health care professionals should allow for such rapid changes, and a platform of rapid exchange of information and advice would be beneficial.
  • 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.
  • The best way for countries to prepare for this, is to have regular simulation exercises that take these issues into account.