Survey 2: Wastewater Health Surveillance

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Key Findings

  • Wastewater sampling is an innovative health surveillance approach that has been trialled during the COVID-19 pandemic. 
  • Our survey asked people for their preferences for when and how their wastewater should be sampled for monitoring COVID-19
  • For one section of the survey, our headline initial findings are that people would prefer to have their wastewater sampled when:
    • UK COVID-19 Alert level is higher, 
    • the wastewater sampling size is larger (e.g., sampled at county level as opposed to street level),
    • it is being shared with a Public Health Body or the Local Authority, rather than a Regional Police Force or a Commercial Company 
  • Many of these findings are consistent with our previous data-driven approaches to COVID-19 public perception survey which can be found here.


During the pandemic several methods have been employed to monitor the prevalence and spread of COVID-19, including regular at home testing and contact tracing apps. In tandem, an innovative health surveillance approach has been trialled – wastewater sampling.  Someone who has COVID-19 will shed fragments of the virus into their faeces, which then enter the sewage system when they go to the toilet1. Therefore, taking a sample of wastewater from the sewage system and analysing it to detect these fragments of the virus can indicate the presence and prevalence of COVID-19 outbreaks. It has been found that such samples can be taken at different places in the sewage system (such as a water treatment plant or the sewer exit of an individual building, for example), with the number of people’s waste likely to be included in the sample varying in relation to the sampling point2. With the novelty of this approach, and it being minimally onerous in comparison to the other initiatives that the UK public has been encouraged to engage in, we wanted to investigate people’s preferences for when and how their wastewater is sampled.

Our Survey 

Our survey design was based upon that of our larger survey (see here and here for blogposts on this larger survey, and here for our snapshot report), and centred around a Choice-based Multiple Conjoint Activity, a method whereby an overall decision can be deconstructed into its component parts (namely, the attributes) and the effects of these attributes can be investigated. We presented our participants with a series of data sharing scenarios. Each scenario defined 3 attributes – (I) what the Covid-19 Alert level was, (II) the wastewater sample size (how many people’s wastewater is likely to be included in the sample), and (III) who the data was being shared with (see the table below for the different options that these attributes were broken down into).

We designed the survey so that the name of the Public Health Body would change based on the participant’s answer to the question “What is your current country of residence?” earlier in the survey. For example, if a participant had answered “Scotland” then the data sharing scenarios would describe the Public Health Body option as “Public Health Scotland”. Also, rather than using a real-life company and risk participant’s being biased based on their prior experiences or impressions of that company, we invented a fictional company (“Info-Insight”) to be the commercial company option in the survey.

We presented these data sharing scenarios in pairs, like in the screenshot below, asking our participants to compare the two scenarios and select the one in which they would be more willing to share their data. Each data sharing scenario and the scenario it was being compared to was designed to maximise the data collected in as few questions as possible (in our case, 17 data sharing scenario comparisons). In some cases the two data sharing scenarios being compared were very similar, in other cases they were very different. It would be difficult to remember what all the different options were, so participants were able to hover their mouse over any underlined text and a little box (a tooltip) would appear providing a description.

We collected a nationally representative sample (regarding age, sex and ethnicity (simplified to five categories) based on data from the Office of National Statistics) of 299 UK residents.

Some Initial Results

The graph below displays the initial results from analysing the survey’s Choice-based Multiple Conjoint Activity data. Listed down the left-hand side are the three attributes and their options. For each attribute, one of the options is set as the reference, e.g. “(I) Alert level (ref=Level 1)”. The estimates (presented by a dot, the point estimate, with the associated 95% confidence interval) measure the changes in preference relative to the reference option. To help interpret the estimates, a vertical dashed line down the figure is added to indicate if there is no difference in preference between the option of interest and the reference option. The further away an estimate is from the dashed line, the greater the preference (if to the right) or the lesser the preference (if to the left) the participants showed for scenarios that included that option in comparison to the reference option. Statistical evidence of the presence or absence of a difference in preference is presented via the 95% confidence interval, the two vertical bars to either side of the dot. An interval overlapping with the dashed line indicates little evidence of a difference in choice preference between the option of interest and the reference option. Otherwise, the data suggest a considerable difference in choice preference.

The results, as displayed in the graph, are: 

(I) Participants preferred scenarios where the wastewater sample was being collected when the UK COVID-19 Alert Level was higher. 

(II) Participants preferred scenarios where the wastewater sampling size was larger. 

(III) Participants preferred scenarios where the organisation receiving the results of their wastewater sample were their Public Health Body and Local Authority, rather than a commercial company (Info-Insights) or their Regional Police Force. 

Some Final Thoughts 

Extending our discussion of the Choice-based Multiple Conjoint Activity results further, it is interesting to compare them to the results of our previous, larger survey. Regarding the attributes that are present across the two surveys (UK COVID-19 Alert Level, and Data holder), the relative preference for these is consistent. The findings from both surveys are that data-sharing in scenarios where the Alert Level is 5 is preferred over level 3, and level 3 is preferred over level 1. Regarding the data holder, in both surveys we found that scenarios where the data was being shared with a Public Health Body was most preferred, with Local Authorities coming second, and the least preferred scenarios were when data was being shared with the Regional Police Force or a Commercial Company. This is interesting considering that the data being shared – medical or mobility data, and the results from wastewater sampling – differ dramatically. 

Finally, to extend our analysis of the Choice-based Multiple Conjoint Activity data from the wastewater survey further, we will consider whether the results differ by demographics such as age, gender, and ethnicity. But before that, our next blogpost will report our findings from grouping our participants in terms of how they rated their willingness to share data in both the scenarios they preferred and did not prefer. So, stay tuned for part 2! 


  1. Department of Health & Social Care. ‘Wastewater testing coverage data for the Environmental Monitoring for Health Protection (EMHP) programme.’ 10th June 2021.  
  1. Matthew Wade, Davey Jones, Andrew Singer, Alwyn Hart, Alex Corbishley, Christopher Spence, Mario Morvan, Chaoyi Zhang, Mark Pollock, Till Hoffmann, Peter Singleton, Jasmine Grimsley, Josh Bunce, Andrew Engeli, Gideon Henderson, ‘Wastewater COVID-19 Monitoring in the UK: Summary for SAGE – 19/11/20’. 19th November 2020.