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Why settings in which people may have become infected are not always shown on the dashboard

This article describes how contact tracing was carried out by the municipal health services (GGDs) up until 4 November 2021. As of 5 November GGDs have adopted a new, tailored approach to contact tracing. With tailored contact tracing, sufficient information on possible transmission settings is more often available and can therefore be presented on the dashboard. For more information about this change, please see the Explanation of the data presented.

Employees are carrying out contact tracing

This article explains the information on the pages (national and by safety region) about contact tracing .

When someone tests positive for coronavirus, the municipal health service (GGD) investigates where this person could have become infected. This is called contact tracing. If many people in the same region test positive, the GGD has to do a lot of contact tracing. This can be so time-consuming that it is only possible if the investigation is less comprehensive. The information obtained is still useful, but does not provide enough data for the dashboard. Read all about risk-based contact tracing in this article.

Comprehensive or risk-based contact tracing

Contact tracing can be carried out at different levels of intensity, ranging from 1 (full investigation) to 5 (the GGD only phones people to report a positive result).In between are a number of forms of risk-based tracing (levels 2 to 4). The level of contact tracing carried out by a GGD depends on the number of infections in the region concerned.

The picture below shows the steps taken by the GGD at each level. When all the steps of a level have been completed, the investigation is finished. It does not mean that the investigation automatically moves to the next level.

Explanation of the contact tracing levels

If possible, the GGD conducts comprehensive contact tracing (level 1). This takes 8 to 12 hours for each person who tests positive. If a lot of people test positive, it is not always possible to conduct a full investigation at level 1 or 1b. In this event, the GGD only carries out risk-based contact tracing (levels 2, 3 or 4). This could mean that a person who has tested positive personally informs their contacts that they may also be infected and need to go into quarantine.In exceptional circumstances, when it is extremely busy, the GGD may only have time to call people to tell them their test results (level 5).

Less data from risk-based contact tracing

Risk-based contact tracing usually means the person who tests positive must inform their contacts themselves. This reduces the chance that a contact who later also tests positive will know who transmitted the virus to them. In other words, risk-based contact tracing means the GGD gets less data about where someone may have been infected.Additionally, there is not enough of this data to give a full picture of the situation. The regions where this is the case are shown in grey on the dashboard (see example below).

Settings in which people may have become infected by safety region

A GGD must have conducted level 1 or 1b contact tracing for a full week for there to be enough data to give a reliable overview of the situations in which people may have been infected.Regions with sufficient data are shown in blue on the dashboard. The dashboard only gives up-to-date data for the blue regions.

Level of contact tracing can change

Each GGD decides for itself what level of contact tracing it can conduct at any given time. This depends on the GGD’s available capacity and the number of people in the region who have tested positive.

If level 1 contact tracing is no longer possible because too many people have tested positive, then the GGD will decide which level is feasible. The same applies in reverse – if contact tracing is being carried out at level 3 and it is no longer as busy, the GGD will revert to level 2 or 1 if possible.

If a GGD is temporarily unable to conduct level 1 or 1b contact tracing, this is shown in the graph ‘Situations in which people may become infected: developments over time’.

Settings in which people may have become infected: developments over time

The graph above shows two grey bars. These are periods when a GGD was unable to conduct level 1 or 1b contact tracing, so no information can be given on the dashboard. The availability of data may vary between safety regions.