Using coronavirus monitoring in sewage to fight COVID-19

Roadmap for Municipal Public Health professionals | Deze pagina in het Nederlands

Version March 11, 2022

These guidelines are designed to show Municipal Public Health Services (GGD) professionals how to use the sewage measurements as shown on the Coronavirus Dashboard provided by Central Government. These guidelines are intended to support doctors working in infectious disease control at the Municipal Public Health Services in gaining an understanding of the transmission and epidemiology of COVID-19 based on wastewater figures. Changes in the circumstances of the epidemic, such as an increasing vaccination coverage, cause the relationship between and interpretation of the indicators of hospital admissions and positive tests to fluctuate. This may increase the relevance of wastewater figures. The wastewater figures may contribute to determining the level of infection in the region in conjunction with other indicators.

roadmap

Figure 1. The action values apply to the wastewater figures for the catchment areas of wastewater treatment plants (WWTPs). These figures are available on coronadashboard.government.nl. Go to safety regions and click on the relevant safety region on the map. Click on Early indicators, Virus particles in wastewater (bottom). Scroll to the ‘Average number of virus particles over time’ chart. Select location, which will show you the WWTP locations.

1. Introduction

Since the beginning of 2020, RIVM has been carrying out measurements to quantify the SARS-CoV-2 virus in wastewater in the Netherlands. From the beginning of September, measurements have been carried out at over 300 locations, which relates to all wastewater treatment plants (WWTPs). The results have since been published on the Coronavirus Dashboard. More information on sewage research is available in the Wastewater Measurements on the Government Coronavirus Dashboard brochure (in Dutch), developed for and in consultation with the Municipal Public Health Services.

On the Coronavirus Dashboard, wastewater measurements are shown at national level as well as broken down by safety region and by municipality. Multiple municipalities may discharge wastewater at a single WWTP. Conversely, a single municipality may discharge wastewater at several WWTPs. The allocation of the number of virus particles per municipality is based on the number of connected residents. As a result, allocation per municipality is an approximation of the actual number of virus particles discharged.

The purpose of this step-by-step plan is to provide clarity and potential actions to be taken based on the trends in wastewater measurements. Trends in wastewater measurements may, for example, relate to an increase or decrease. These trends are associated with specific action values and potential actions at the level of a WWTP. The wastewater measurements per WWTP are available on the Coronavirus Dashboard under the various safety regions, but they are also specified individually at municipal level. The overview of all WWTPs shows which GGD region covers a specific WWTP and what its corresponding water board is, as well as what percentage of the wastewater of a particular WWTP comes from residents of the relevant GGD region. This same document also shows which municipalities are connected to the WWTP and what the corresponding postcode area is (PC4 level).

Various potential actions are provided for each action value. Ultimately, the Municipal Public Health Services will determine what action will be taken at local level. The wastewater figures can serve as a supplement to the regional surveillance that takes place within the GGD and may contribute to accounting for the spread of the SARS-CoV-2 virus in the GGD region.  

2. Step-by-step plan overview

There are four distinct action values depending on the trend of the wastewater figures. These action values are not consecutive in nature but are linked to the trend of the wastewater figures at WWTP level. The action values are related to the stage of the epidemic, depending on the classification of the risk level in the Netherlands (caution, concern and serious). It is therefore vital to always take into account i) the national trend of the wastewater figures and ii) the stage of the epidemic based on other indicators. If the trend at WWTP level stands out compared to the above, we recommend caution. A distinction is made between the following four action values (see Figure 2):
 

  • Action value 1: wastewater figures show a plateau with high values.
  • Action value 2: wastewater figures show a downward trend.
  • Action value 3: wastewater figures show viral loads after at least 14 days during which the virus was not detectable in the wastewater.
  • Action value 4: wastewater figures show an upward trend.

graph with detection limit per action value
Figure 2. Trends in the wastewater measurements shown when the four distinct action values are reached: a plateau characterised by high values (Action value 1), a downward trend (Action value 2), a resurgence, with wastewater figures showing viral loads after at least 14 days during which the virus was not detectable in the wastewater (Action value 3), and an upward trend (Action value 4). The wastewater measurements are represented by the dark blue curve, while the boundaries of the stages during which the action values apply are shown using dotted light blue lines. The detection limit, below which a virus cannot be detected is shown in red
.

2.1 Action value 1

The wastewater figures show a plateau where the wastewater figures exceed 100 x 100 billion (1013) virus particles per 100,000 residents on more than 14 days in a row. At this stage, the recommendation to continue to enforce the measures depends on the risk level applicable in the Netherlands (caution, concern or serious). The applicable risk level is based on the average number of hospital admissions and the average number of ICU admissions within a 7-day period and therefore takes into account the stage of the epidemic we are in at that moment.

2.2 Action value 2

The wastewater figures show a declining trend. At this stage, we recommend that the wastewater figures be monitored in order to quickly be able to flag any potential change in the trend. The increasing vaccination coverage could be a possible cause of the downward trend in the wastewater figures, given that vaccinated people lead to fewer infections taking place, resulting in less viral shedding. At present, no information is available regarding the viral load in the faeces of vaccinated people compared to unvaccinated people.

It may be that the downward trend in the wastewater figures differs from the trend in hospital admissions, positive tests and/or percentage of positive tests. In this case, we recommend remaining vigilant and raising this observation within the surveillance structure of the GGD (Municipal Public Health Services).

2.3 Action value 3

The wastewater figures show that there is SARS-CoV-2 or a revival in SARS-CoV-2 circulation within the catchment area of the WWTP. It is vital to monitor whether or not this trend will persist. If the indications provided by the wastewater figures differ from positive tests and/or hospital admissions, we recommend monitoring the situation more closely. In the event that wastewater figures show virus particles after 14 days during which the virus was not detectable, the following range of options are available:  

 

  • Identifying the spread of COVID-19 within the municipality based on other indicators

    Are there any data on hospital admissions or positive tests that could potentially account for the revival shown by the wastewater figures?
    You may be able to interpret the indicator identified by the wastewater figures by examining indicators at local level that provide a picture on the spread of SARS-CoV-2 in the relevant municipality and, if possible, at district level. This includes the incidence of infections, willingness to test for COVID-19, vaccination coverage, occurrence of so-called SARS-CoV-2 Variants of Concern, the percentage of positive tests and clusters within the municipality as well as at locations that often come up in Source and Contact Tracing (SCT) not associated with any known cluster. These figures should also be compared to surrounding municipalities where wastewater figures may not yet be positive.

  • Identifying the origin of the indicator: profiling the relevant municipality in consultation with the municipality and water board

    Are there any high-risk locations within the municipality from which the indicator could have originated?
    Identify whether there are any high-risk locations within the municipality or in adjacent municipalities that can account for the indicator. This includes hospitals, asylum seekers’ centres, care institutions or other locations at which large numbers of people could be shedding the virus simultaneously, such as large companies, large-scale student accommodation and schools. In addition, information from GPs remains a key source of information. There may also be locations that can distort the indicator shown by wastewater, such as industry. Furthermore, recreational areas may also contribute to a distorted picture. If a municipality includes a recreational area that is visited by a large number of holidaymakers who live outside of the municipality, then more people may be shedding virus particles than the number of connected residents. This may lead to a distorted picture, given that the viral loads are calculated on the basis of the number of connected residents per wastewater treatment plant, which remains the same over time. Any high-risk locations and locations that may distort wastewater figures should be identified in collaboration with the municipality.
    In the event of any ambiguity in interpreting or specifying the indicator, consultation can take place with the relevant water board. It may be possible to carry out additional research, for example, into the wastewater flows or to schedule additional sampling at district level in collaboration with the water board
    .

  • Focusing on Source and Contact Tracing (SCT) to identify an indicator shown by wastewater figures

    The Municipal Public Health Services (GGD) may choose to focus on Source and Contact Tracing (SCT) to account for the indicator demonstrated by the wastewater figures. The intensity of the SCT will depend on the capacity within the GGD. At the point where SCT does not yield any additional information, you may consider focusing on a local communications strategy or a low-threshold risk-based testing strategy. In the case of new outbreaks, we recommend identifying the SARS-CoV-2 variant.

  • Contacting RIVM with any questions or to clarify any ambiguities

    In the event of any questions regarding the interpretation of the figures and any control measures, please phone the National Coordination Centre for Communicable Disease Control (LCI) on the following number: 088-6897000.

2.4 Action value 4

The wastewater figures indicate increasing circulation of SARS-CoV-2 in the relevant catchment area. It is vital that you closely monitor whether this trend in the wastewater figures persists and/or other indicators are following this trend.

If the trend continues, we recommend further intensifying SCT and focusing on implementing an additional local communication or large-scale risk-based testing strategy in districts using mobile testing units or setting up local testing sites. In this case, the wastewater figures can serve as one of the indicators within the GGD surveillance structure.

In the event that the wastewater should exceed the value of 100 x 100 billion (1013) virus particles per 100,000 residents, similar to Action value 1, we recommend continuing to enforce measures depending on the applicable risk level in the Netherlands.

3. Evaluation

If you are using the wastewater figures as an additional indicator in regional surveillance, please report this to RIVM by sending an email to afvalwatersurveillance@rivm.nl with the subject line: Evaluation of wastewater figures in regional surveillance.

4. More information

Additional information on wastewater research and publication of the data on the Coronavirus Dashboard is available in the Wastewater Measurements on the Government Coronavirus Dashboard brochure (in Dutch) developed for and in collaboration with GGD professionals.

An overview of all WWTPs in the Netherlands has been attached to this step-by-step plan. This overview specifies which GGD regions and water boards cover the individual WWTPs. It also shows which municipalities and corresponding postal codes (PC4) discharge at which WWTPs.   

Version control

  • 11-03-2022: First translated version.