Like you I have been tracking the Scottish wastewater monitoring and always wondered why the lag between ‘wastewater’ to case peaks ‘reversed’ when Omicron arrived. You may already have seen it but there was a great paper in the Journal of Water & Health that reviewed Scottish wastewater monitoring and how it informed policy making. It’s worth a read.
They answer my question on how they adjusted for dilution due to sporadic rainfall -- it’s all to do with flow rates and ammonia levels (I think they were too polite to mention what the last one really measured).
Anyway the paper describes how they deal with the outliers you mentioned and talks about the Omicron effect. They note that detection became more difficult with Omicron due to a reduction in the ‘Covid shedding rate’ and changes to case ascertainment due to changes in testing policies. Although I suspect that the story is more complicated than that.
Not a stupid question at all, but the basic reason is that they last for only a day or two and then plummet back again. That's not a real COVID infection, or if it is, it's not an effect which is anything like thousands of people getting infected all at once and then getting better 24 hours later.
Ah, okay. That’s v cool in and of itself, but also cool to think about for non-case/detection transmission. It’s fair to assume those instances of detection in wastewater without a test-positive are reflecting an immune response, right?
Like you I have been tracking the Scottish wastewater monitoring and always wondered why the lag between ‘wastewater’ to case peaks ‘reversed’ when Omicron arrived. You may already have seen it but there was a great paper in the Journal of Water & Health that reviewed Scottish wastewater monitoring and how it informed policy making. It’s worth a read.
They answer my question on how they adjusted for dilution due to sporadic rainfall -- it’s all to do with flow rates and ammonia levels (I think they were too polite to mention what the last one really measured).
Anyway the paper describes how they deal with the outliers you mentioned and talks about the Omicron effect. They note that detection became more difficult with Omicron due to a reduction in the ‘Covid shedding rate’ and changes to case ascertainment due to changes in testing policies. Although I suspect that the story is more complicated than that.
https://iwaponline.com/jwh/article/20/12/1688/92556/Wastewater-monitoring-of-COVID-19-a-perspective
That's a really interesting paper, thank you for pointing it out.
This may be a stupid question, but I’m wondering why we can assume the “spurious peaks” you describe are only that.
Not a stupid question at all, but the basic reason is that they last for only a day or two and then plummet back again. That's not a real COVID infection, or if it is, it's not an effect which is anything like thousands of people getting infected all at once and then getting better 24 hours later.
Ah, okay. That’s v cool in and of itself, but also cool to think about for non-case/detection transmission. It’s fair to assume those instances of detection in wastewater without a test-positive are reflecting an immune response, right?