This article's from back in December of last year:
Australian study shows wastewater testing can detect coronavirus weeks before people show symptoms - ABC News
Can someone more science-ey please explain just how we keep detecting it in poo in areas where there are never any resulting confirmed infections? The article above seems happy to plod along under the assumption that it's been circulating in people who are asymptomatic but that just doesn't add up. The latest research into symptomatic buggers vs your typhoid marys suggest it's as low as 17% of covid cases that are asymptomatic or roughly 1 out of every 5. Even if it were skewed the other way and for every 5 asymptomatic cases there was just 1 who showed symptoms there would still be news of an outbreak in the sort of timeframes they're talking about.
Something doesn't smell right!
The only logical explanation I can think of is there's a common or garden coronavirus that's been around for donkeys years (possibly the common cold?) that resembles Covid 19 when it's been swimming amongst the Mersey Trout but we've just never tested for it before, but surely the poo boffins would have considered this?
Now my mind may be biased by the fact I've just finished another rewatch of The Wire but I can't help but think this sounds like McNulty's 'Serial Killer' in season 5! Is this just a ploy to get more funding so they can test more poo?
The work is based on the premise (or findings) that covid sufferers shed the covid RNA in their stool after they are infected. There have been previous studies about this, so it is likely to be true.
If you read through the paper - I won't go through it in great detail, but essentially, the methods they used to extract the viral RNA from the wastewater samples yield inconsistent results for both positive and negative samples. One of methods they used, from my understanding, basically counts the number of copies of the virus per litre of samples. If there are only small amount of virus in the samples, then this method is a hidden miss. Then they did some mathematical simulation to identify whether the presence of the virus in the stool and wastewater is in any way correlated with the positive cases, and as expected, the first yield a high correlation.
The paper also highlighted other studies which over-estimated the number of positive cases (from the wastewater). The model only found correlation between virus in stool and positive cases, and did not have the ability to reliably correlate the actual number of positive cases with the copies of viral RNA in the wastewater or stool (it wouldn't have been possible with the method they used anyway). EDIT: they actually have a formula to estimate the number of cases based on number of viral RNA copies, poop amount, wastewater amount, etc, but my guess is that even that is an over-estimation.
More importantly, this study is a proof of concept that have been shown to be promising. As with any biological experiments, there were likely to be only small sample sizes, which elevated the possibility of spurious results. As the authors noted, the method is promising, but larger sample size is required. They also noted the need for more reliable way of extracting the RNA of the virus from the sample, and that it is very hard to reliably quantify the presence of the virus if there is only a small amount of it.
So tldr, yes the method can reliably find positive cases if there were many of them, but in the case of only a small number, it struggles, as expected. Moreover, if you have covid, chances of the virus being present in your poop is very likely.
Have a read of the paper if you are interested:
https://www.sciencedirect.com/science/article/pii/S0048969720322816. Just focus on the intro and discussion if the result section is too much.