Wastewater testing coverage data for the Environmental Monitoring for Health Protection (EMHP) programme
Published 10 June 2021
Applies to England
© Crown copyright 2021
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This publication is available at https://www.gov.uk/government/publications/wastewater-testing-coverage-data-for-19-may-2021-emhp-programme/wastewater-testing-coverage-data-for-the-environmental-monitoring-for-health-protection-emhp-programme
Data for the coverage of wastewater testing in England as part of the Environmental Monitoring for Health Protection (EMHP) wastewater surveillance programme.
Background on the Environmental Monitoring for Health Protection (EMHP) wastewater surveillance programme
People who have had COVID-19 shed the virus during daily activities such as going to the toilet and blowing noses. The virus enters the sewer system through sinks, drains and toilets. Fragments of the SARS-CoV-2 virus (the virus that causes COVID-19) can be detected in sewage samples.
The EMHP programme, led by the Joint Biosecurity Centre (part of NHS Test and Trace), tests sewage for fragments of SARS-CoV-2 RNA. Samples are taken from sewage flowing into wastewater treatment plants and from key locations across the sewer network (manholes) on a daily basis.
The programme helps identify where the virus is circulating in England, detecting spikes in prevalence and helping to inform localised action. It has the benefit of detecting the virus in asymptomatic individuals. Wastewater monitoring compliments other testing programmes and public health actions to help protect against the threat of new variants, as the country closely follows the roadmap out of national restrictions.
As the threat of variants has emerged, the programme now plays an important role in the detection of mutations of the virus, variants of concern (VOCs) and variants under investigation (VUIs). This is done through genomic sequencing of wastewater samples, to provide an indication of where VOCs and VUIs may be present across England. The wastewater surveillance programme routinely sequences samples from sewers across the country to provide a national and local view of the presence of mutations and variants. Insights from wastewater testing are shared with local and national decision makers, to help inform the action that they can take to stop further transmission.
The programme is led by the Joint Biosecurity Centre and run in partnership with the Department for Environment, Food and Rural Affairs, the Environment Agency, the Centre for Environment, Fisheries and Aquaculture Science, academia and water companies. It provides coverage to approximately 70% of the population of England. The EMHP team coordinates with programmes in the devolved administrations to provide UK-wide wastewater monitoring.
Wastewater testing coverage data
Table 1 shows the percentage of each regional population in England covered by wastewater sampling (based on coverage on 19 May 2021). Population coverage estimates are produced by matching lower layer super output areas (LSOAs) and their associated populations to wastewater catchments. There are several sources of uncertainty in these estimates, for example in how LSOAs are matched to the catchments and uncertainty about catchment boundaries (see Methodology below for further information). EMHP estimate this uncertainty to be approximately ± 15%.
Table 1: percentage of regional populations covered by EMHP wastewater sampling
| Region | Wastewater testing coverage population estimates | Region population estimates | Percentage estimate of regional population covered by wastewater testing |
|---|---|---|---|
| North East | 1,719,000 | 2,670,000 | 64% |
| North West | 4,895,000 | 7,341,000 | 67% |
| Yorkshire and The Humber | 3,509,000 | 5,503,000 | 64% |
| East Midlands | 3,008,000 | 4,836,000 | 62% |
| West Midlands | 4,491,000 | 5,934,000 | 76% |
| East of England | 4,058,000 | 6,236,000 | 65% |
| London | 8,952,000 | 8,962,000 | 100% |
| South East | 5,494,000 | 9,180,000 | 60% |
| South West | 3,353,000 | 5,625,000 | 60% |
| England | 39,480,000 | 56,287,000 | 70% |
This data and data for lower-tier local authorities (LTLAs) are available in the accompanying spreadsheet, ‘NHS Test and Trace: wastewater testing coverage, 19 May 2021’.
Figure 1: percentage of LTLA populations covered by EMHP wastewater sampling
Methodology
About this data
The population coverage estimates reflect the population covered by wastewater catchments where the EMHP programme samples wastewater and tests for SARS-CoV-2 (the virus that causes COVID-19). The estimates represent a snapshot of the coverage of wastewater surveillance as of 19 May 2021.
We continue to explore the feasibility of publishing new information. We intend to publish additional data from the EMHP programme, including concentrations of SARS-CoV-2 RNA detected in wastewater.
Data sources
The population estimates of regions, LTLAs and LSOAs (a standard Office for National Statistics (ONS) geography, with each LSOA containing approximately 1,500 people[footnote 1]) are ONS estimates and are mid-2019 estimates of population. The population-weighted centroids of LSOAs used in the LSOA-to-catchment matching algorithm (see ‘Estimating wastewater testing population coverage’ below) are also sourced from ONS.
The catchment boundaries for sewage treatment works (STWs) were provided by the 9 water companies serving England:
- Severn Trent
- South West Water
- Southern Water
- Wessex Water
- Thames Water
- Anglian Water
- Northumbrian Water
- Yorkshire Water
- United Utilities
Estimating wastewater testing population coverage
EMHP sample at sewer network sites (manholes in the street which generally serve a local area) and STWs (which generally serve wider areas such as a city or town). Associated with every STW and sewer network site that EMHP sample at is a catchment, which is the area from which wastewater flows into the sampling location. Sewer network sites almost always fall within the catchment of a STW, so generally network sites do not count towards population coverage.
To estimate the population of catchments, EMHP matched LSOAs to all the catchment areas sampled (both sewer network sites and STWs). If the population-weighted-centroid of an LSOA falls within the boundary of a catchment, then the whole population of the LSOA is assigned to that catchment. If an LSOA is served by multiple sites, such as an STW and a network site, it is only counted once.
To calculate the population coverage in a region, a matching algorithm between LSOA and wastewater catchment is used to determine which LSOAs are served within a region.
The sum of the populations of the LSOAs covered by EMHP samples in the region is divided by the region population to calculate the percentage coverage for the region. Similarly, the national coverage figure is calculated by summing the population covered in every region and dividing by the population of England.
Uncertainty, data quality and revisions
The data presented provide a snapshot of wastewater testing coverage on 19 May 2021. The data has a degree of uncertainty and associated caveats:
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The sites from which EMHP sample can change depending on testing capacity, epidemiological priorities and current local response activities, resulting in changes to the population covered
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Associated with every STW and sewer network site that EMHP sample at is a catchment, which is the area from which wastewater flows into the sampling location. The process of matching LSOAs to catchment areas is approximate. There is uncertainty in the matching process where LSOAs partially overlap the catchment boundary. This uncertainty is increased by other data quality issues and uncertainties:
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the boundaries of wastewater catchments are mostly constant but can change depending on factors such as rainfall, as storm drains divert the flow of water to different parts of the network
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catchments of a site can change, particularly as there is uncertainty about the catchment areas of STWs (given that one water company can own the STW and a different water company can own the sewer infrastructure). This may mean that a STW serves a different catchment area to the one EHMP has assigned to it
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These data quality issues affect a minority of catchments, and EMHP are confident in most catchment boundaries
If any substantial revisions occur in future publications of this data, this will be outlined in the publication. DHSC has published a revision policy for official statistics.