Spread of the virus
Where do these figures come from?
The figures for wastewater testing are supplied by the National Institute for Public Health and the Environment (RIVM) as open data.
- See RIVM’s open data set of wastewater measurements
- See RIVM’s description of the data set of wastewater measurements
How are the figures determined?
Wastewater samples are collected at wastewater treatment plants across the country, so that data is available for all of the Netherlands. The samples of untreated wastewater are kept chilled during transport to RIVM. RIVM researchers analyse the samples and determine how many coronavirus particles each sample contains. Three times a week on average for each location, researchers test one sample of wastewater collected over a 24-hour period.
It takes several days before the outcome of an analysis is known. That is why the dashboard does not show measurements from the most recent days. The number of samples that can be analysed successfully differs from one week to the next. The open data file shows the date and location of successful measurements. If the number of virus particles in a sample is too low to be measured, the value is recorded as 0. This monitoring method is still under development.
Assisted by the water authorities, Statistics Netherlands (CBS) has calculated the number of inhabitants served by each wastewater treatment plant, so that RIVM can determine the number of virus particles per 100,000 inhabitants.
From 30 December 2022 onwards, the RIVM will make use of an updated version of the file that is provided by Statistics Netherlands (CBS), that describes the number of inhabitants per wastewater treatment plant care-area. The updated file contents will be retroactively applied to all sewage measurements from 2022.
Change in number of measurements per week 6 February 2023
As of 6 February 2023 RIVM has reduced the number of measurements per location from 4 to 3 per week. In the current phase of the pandemic, this is sufficient to keep a good eye on the virus.
Sewage data 26 September 2022
According to the RIVM, the results of the sewage measurements of Monday 26 September 2022 do not provide an accurate picture of the amount of virus particles in the sewer. This is because a lot of rain fell all over the country while the samples were taken. Therefore, these measurements will not be published in the open data.
Changes in the figures
A measurement of 26 August 2021 from sampling location Dinther with a very high result, was published on the dashboard on 31 August 2021. This measurement also caused a large increase in the national figures. Because the value was so extreme and RIVM, after quality checks and research, has not found an explanation, RIVM has removed the measurement from the data on 1 September 2021. RIVM has conducted further research into other measurements from the same period. The results of samples taken on 25 August 2021 and on 30 August 2021 are available on the dashboard.
From 4 March 2021 the dashboard also shows wastewater monitoring results for municipalities that do not have their own wastewater treatment plant. This is possible by using the measurements from all wastewater treatment plants that serve a municipality. Other figures were adjusted at the same time. To find out how the figures are calculated, see ‘How are the figures determined?’.
In 2020 two sampling locations were ended. Sampling for their catchment areas was taken over by two other locations. In the week of 5 October, the location at Aalst was taken over by Zaltbommel, and in the week of 7 December, the location at Lienden was taken over by Tiel. So the figures calculated for the locations at Zaltbommel and Tiel before that time are based on a lower number of inhabitants. You can find these numbers, as well as those of Aalst and Lienden, in a table compiled in 2020 by Statistics Netherlands (CBS).
Sewage data Woerden
From February 3, 2022, the Coronadashboard will no longer show sewage water measurement for the municipality of Woerden. The Ministry of Health, Welfare and Sport and the National Institute for Public Health and the Environment (RIVM) have decided this because the measurements of the municipality of Woerden consistently showed extremely high values. This trend was not seen in other indicators, such as the number of positive tests. The RIVM has therefore conducted further research to determine the deviation. The sewer system has been examined at various locations in the municipality. No explanation has been found so far, but the investigation continues. It has become clear that the deviation cannot be explained by the number of infected people in the municipality.
Sewage data Katwoude
From August 18, 2022, the Coronadashboard will no longer show sewage water measurement for the municipality of Katwoude. The Ministry of Health, Welfare and Sport and the National Institute for Public Health and the Environment (RIVM) have decided this because the measurements of the municipality of Katwoude consistently showed extremely high values. This trend was not seen in other indicators, such as the number of positive tests. The RIVM has therefore conducted further research to determine the deviation. The sewer system has been examined at various locations in the municipality. No explanation has been found so far, but the investigation continues. It has become clear that the deviation cannot be explained by the number of infected people in the municipality.
Removal of four extremely high measurement results from the dataset.
The sewage measurements of sewage treatment plant Dokhaven of 21 February 2021, the plant at Veenendaal of 21 March 2021, a plant at Ameland of 22 July 2021 and a plant at Beilen of 8 November 2020 have been removed from the Corona dashboard on 3 February 2022.
The results of these measurements were very high and strongly deviated from regional and national trends in sewage research. Other indicators, such as the number of positive tests, also showed a different picture. In new measurements with new samples, the values appeared to fall within the limits of what is normally seen.
RIVM has therefore decided, together with the Ministry of Health, Welfare and Sport, to extract the measurements of the aforementioned data from the open data. The RIVM has established a protocol on how to deal with these kinds of high values from now on.
Infectieradar
Where do the numbers come from?
Self-reported positive tests
The figures on the percentage of Infectieradar participants who reported a positive test result, come from RIVM. This data is available as open data and presented on the website of Infectieradar.
Participants of Infectieradar are asked weekly to complete a short questionnaire. This questionnaire asks about complaints that may be related to the corona virus. To get the best possible picture of the spread of the coronavirus, it is important that as many people as possible participate, regardless of background, age or risk factors. It can also help to understand why some people get an infection more or less often.
How are the numbers calculated?
For the calculation of the percentage of positive test results, only those participants who have completed at least one questionnaire in that calendar week are taken into account. A calendar week runs from Monday to Sunday.
Questionnaires and positive tests of new participants are not included in the first week of their participation. The results of the submitted nose and throat samples of the self-test study that has been running since September 2022 are also not included in the calculation of the positive percentage.
Self-test research
In the fall of 2022, Infectieradar will be expanded with a self-test study. This research will last until 21 May 2023. The aim of the research is to gain even better insight into the number of virus infections and how this affects the health of people in the Netherlands. Participants in this study may be asked to take a nose and throat sample if they have completed a corona self-test. RIVM is still looking for participants for this low-threshold study.
- Register here if you want to participate in Infection Radar or the self-test study.
- View the explanation about the self-test examination
Postieve testen GGD
Where do these figures come from?
The figures on the number of positive tests (confirmed cases) are supplied by the National Institute for Public Health and the Environment (RIVM). This data is available as open data.
- See RIVM’s open data file on confirmed cases
- See RIVM’s description of the data set on confirmed cases
How are these figures determined?
The figure shows the number of positive tests reported to RIVM in the preceding 24 hours, up to 10.00 on the day of publication of the figures. The date attributed to positive tests is the date on which RIVM was notified by the municipal health authority (GGD). This is not the same as the date on which people are tested.
Doctors and laboratories are required to report cases of infectious disease to the GGD. However, coronavirus tests are also carried out by commercial organisations and individuals. The results of these tests are not always reported to the GGD, or the notification is not counted as the test used does not meet RIVM standards. Commercial testing organisations are required to report positive test results to the GGD. This means that the daily number of confirmed cases reported on the dashboard may not give the complete picture. This should be kept in mind when interpreting these figures.
Part of the notification process is done manually. Sometimes the GGDs will not have reported all newly confirmed cases at the moment that RIVM compiles the figures for the preceding 24 hours. Missing notifications are passed on at a later time. Missing or delayed notifications can skew the daily figures. The rolling average filters out this type of fluctuation, and therefore often gives a better picture of the number of infections.
- See how the rates per 100,000 people are calculated
- See the explanation of the data on age groups in graphs
- See the description of the rolling 7-day average
Changes in the figures
RIVM can also retrospectively correct data that has already been published. These corrections are processed in the open data file and incorporated into the dashboard. The data file registers cases at safety region and municipality level. In order to calculate data at national level we add all notified cases together. Some notified cases cannot be linked to a particular municipality/safety region, as this information is missing from the data file. These cases cannot therefore be shown at those levels, but they are included in the national figures.
Where do these figures come from?
Twice a week (on Tuesdays and Fridays), the National Institute for Public Health and the Environment (RIVM) supplies open data on the reproduction number. The reproduction number (R) is not an exact value but a reliable calculation.
- See RIVM’s open data set on the reproduction number
- See RIVM’s description of the data set on the reproduction number
How are the figures determined?
RIVM uses the reported number of daily positive test results to calculate R. In most cases, the day on which symptoms first presented is known. In other cases, this date can be estimated. If someone has no symptoms, RIVM will use the date on which they would normally have experienced symptoms for the first time.
Depicting the number of coronavirus cases according to the first day of symptoms gives a clear picture of whether the number of transmissions is increasing, at its peak or decreasing. In order to calculate R, it is also necessary to know the length of time between the first day of symptoms of a new case and the first day of symptoms of the person who infected them. This has been calculated to be 4 days on average, based on coronavirus cases reported to the municipal health service (GGD). This information is then used to calculate the reproduction number.
How up to date are the figures?
The most up-to-date value of R provided on the coronavirus dashboard at any given time is always from at least two weeks ago. Calculations of R using data from less than 14 days ago could provide an indication of what the definitive value may be, but are not reliable predictors. The more recent the day, the less reliable the figure is since not all the data for that day is available yet.
Changes in the figures
From 15 March 2023, the reproduction number will be calculated again based on COVID-19 hospital admissions according to the NICE hospital registration. From 13 June 2020 to 14 March 2023, the reproduction number was calculated on the basis of COVID-19 reports to the GGD. However, the number of reports is strongly determined by the test policy, and is less suitable as a basis for calculating the reproduction number due to the adjusted test policy and the closure of the GGD test lanes as of 17 March 2023. Until 12 June 2020, the reproduction number was also calculated on the basis of hospital admissions, but then as reported to the GGD.
Where do the figures come from?
The figures on coronavirus variants are supplied by the National Institute for Public Health and the Environment (RIVM) as open data.
- See RIVM’s open data set on coronavirus variants
- See RIVM’s description of the data set on coronavirus variants
How are the figures determined?
The National Institute for Public Health and the Environment (RIVM) has been studying coronavirus variants in the Netherlands through pathogen surveillance since late 2020. Every week RIVM analyses about 1,500 random test samples containing coronavirus that it receives from various labs across the country.
On the basis of this analysis, RIVM can determine what percentage of infections each variant is responsible for and, from there, predict the speed at which the different variants are likely to spread. This enables RIVM to estimate what percentage of future infections will be caused by which variant. As new data arrives each week, it is checked against these predictions. This helps make future predictions more and more reliable. The figures shown on the Dashboard are not RIVM’s predictions, but rather the data from the pathogen surveillance. Preparing and analysing the samples and processing the data takes time. The figures for the most recent weeks are therefore incomplete and, because of this, we do not show them on the Dashboard. As a result, the percentage for a given variant as reported by RIVM often differs from what is shown on the Dashboard at that time. The media also tends to report RIVM’s predictions.
The data gathered from pathogen surveillance is updated every Friday. Figures may change from week to week compared to what was previously published, generally as a result of changes to the date a sample was collected or other changes related to the sample in the registration system. Data from the most recent weeks is incomplete and is updated in future publications as more information becomes available. In other words, the data on the dashboard is updated retroactively.
Variants on the dashboard
The table on the dashboard shows the variants of concern and the variants of interest. The European Centre for Disease Prevention and Control (ECDC) and the World Health Organization (WHO) consider a variant to be a variant of concern if it spreads more easily, makes people more sick or if vaccines are less effective against the variant. A variant of interest is a variant that has been traced to multiple infections in a particular setting or cluster, or that has been detected in multiple countries.
The graph on the dashboard only shows the ECDC variants of concern. These variants are monitored because of their potential risk. RIVM follows the ECDC and the WHO guidelines in this respect. The variants that are not shown separately in the graph are listed in the category 'other variants'.
Chart adjustments
As of 3 September 2021 the European Centre for Disease Prevention and Control (ECDC) and the World Health Organization (WHO) are no longer designating the Alpha variant as a ‘variant of concern’, but as a ‘variant of interest’. Since that date, the National Institute for Public Health and the Environment (RIVM) has included data on the Alpha variant in the data set as a ‘variant of interest’. On the graph ‘Coronavirus variants over time’, variants of interests are included in the group ‘other coronavirus variants’. The Alpha variant was therefore not shown separately on the graph between 3 September and 28 October 2021. However, because the Alpha variant was previously a ‘variant of concern’ and was the dominant variant for almost 6 months, an exemption has now been made for this variant. As of 28 October the Alpha variant is shown separately in the graph again.
Where do these figures come from?
General data on mortality is provided by the national office Statistics Netherlands (CBS).
How are the figures determined?
Statistics Netherlands (CBS) weekly publishes the total number of deaths on Friday and compares this number with the expected number of deaths. Excess mortality occurs when more people die than expected. So expected mortality is the mortality you would expect if there had been no corona epidemic. This takes into account factors as aging and migration and compares it with the seasonal pattern from the years before. The predicted number of deaths per week have been taken from the mortality projections made once every year by Statistics Netherlands.
The expected number of deaths has a bandwidth with an upper and lower limit (interval). Statistics Netherlands only speaks of excess mortality if the number of deaths is above the interval. Within the interval, it may be an ordinary fluctuation.
Diffent grouping Weesp
Weesp will merge with the municipality of Amsterdam, as a result of which Weesp will no longer fall under the Gooi en Vechtstreek safety region as of March 24, 2022, but under the Amsterdam-Amstelland safety region. As explained above, when determining the expected mortality for the coming year, mortality in recent years is considered. In order to be able to compare the actual mortality in both safety regions with the expected mortality, Weesp has already been assigned to the Amsterdam-Amstelland safety region on the dashboard from the beginning of 2022.