Speciale COVID-19

Cosa sapere

Faq - Case definition: why surveillance should include all positive cases


The importance of monitoring cases through surveillance should not be confused with the criteria used to decide guidance on cases and contacts. These FAQs summarize the main answers relative to case definitions for the purposes of epidemiological surveillance and to the modalities used to define self-surveillance, quarantine and isolation measures.

1) Why should the definition of surveillance case include all positive cases and not just the cases with symptoms that are indicative of COVID-19 (respiratory symptoms, high fever, altered taste and smell, etc.)?

The symptomatology of the SARS-CoV-2 infection is varied and constantly evolving also because of the appearance of new viral variants which often interact in different ways with our organism. This makes it very difficult to clinically recognize a symptomatic SARS-CoV-2 infection in the absence of laboratory confirmation.

 Experience has also shown that most infections, particularly in vaccinated individuals, are asymptomatic or present very mild symptoms. By not monitoring these cases we would miss the opportunity of identifying emerging variants and knowing their characteristics and we would not know the clinical status that follows the infection in different population groups (e.g. age, vaccination status, comorbidities). We would also miss the opportunity of monitoring the trend of the circulation of the virus over time and, consequently, the risks of a detrimental impact on the ability to maintain adequate levels of health care even for diseases other than COVID-19.

2) Is it true that at European level the ECDC has recently changed the case definition used for the surveillance of SARS-CoV-2 infections and / or cases of COVID-19 disease?

No. The case definition used for surveillance has remained the same since December 2020 and is available online on the website of the European Center for Disease Prevention and Control - ECDC (https://www.ecdc.europa.eu/en/covid-19/surveillance/case-definition). With a view to returning to normalcy after the end of the pandemic emergency, the ECDC suggested in a document dated 18 October 2021 (https://www.ecdc.eurocovid-19-surveillance-guidance.eu/en/publications -data/covid-19 -surveillance-guidance) a future transition to a more sustainable, objective-driven surveillance system, similar to the one currently used for influenza.

3) Does the case definition used in epidemiological surveillance define self-surveillance and quarantine measures?

No. The case definition used for national epidemiological surveillance does not include the contacts of confirmed cases and the surveillance does not monitor their progress over time. Therefore, the definition of case used in surveillance plays no role in defining self-surveillance and quarantine measures. As confirmation of this, on 7 January 2022 the ECDC updated its guidance on quarantine and isolation (https://www.ecdc.europa.eu/en/covid-19/prevention-and-control/quarantine-and -isolation) without changing the case definition used for epidemiological surveillance.

4) Does the definition used in epidemiological surveillance define isolation measures?

No. Although they have in common a need for diagnostic confirmation that makes use of antigenic and molecular tests, a positive case according to the definition of surveillance is evaluated according to a series of criteria, reported in the circular of the Ministry of Health of 30 December 2021 which defines the different methods of isolation.


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