I was more inclined to think that trying to distinguish variants via sewage is intrinsically flawed, since the Omicron "swarm" for an entire city could have some 157del mutants or otherwise just prompt false-positive. But their previous studies show stark transitions using dels to distinguish Alpha and Delta. Which potentially means the …
I was more inclined to think that trying to distinguish variants via sewage is intrinsically flawed, since the Omicron "swarm" for an entire city could have some 157del mutants or otherwise just prompt false-positive. But their previous studies show stark transitions using dels to distinguish Alpha and Delta. Which potentially means the high cycle count isn't as big a flaw either.
RE the model, the math just seems stupid. Delta is staying level until the end. So the model concludes it has to just keep staying level forever, because (as far as I can make out) their equation concludes it will never go high enough to make enough people immune (even though there's tons of prior immunity to Delta). Ok, so your model is idiotic, fix it.
Detecting viral loads in wastewater is a proven concept. The devil of the detail is that the test used has to be of sufficient accuracy and precision to distinguish among potential variants of concern.
That's where the cycle thresholds present a problem--there's considerable evidence to indicate that at higher cycle thresholds (Ct>34 certainly), positive results from viral fragments and dead nucleotides--remnants of prior infection, which are known to linger for quite some time after symptoms have resolved, and can be shed for quite some time after symptoms have resolved.
If the assay is detecting Delta (or Omicron) remnants, the incidence of Delta (or Omicron) is going to be overstated, as the assay was designed to be a quantitative test. Given the fairly recent displacement of Delta by Omicron as the most prevalent variant, including viral fragments in any assessment of the incidence of either variant within a particular population skews the results, possibly dramatically.
That's the other flaw in their modeling--the lack of a discussion about the ratio of "real" cases based on the viral loads found in the wastewater samples and the confirmed cases according to per-patient PCR testing. Without a justifiable ratio estimate to connect wastewater test results to a likely incidence of disease in the community, the only thing the wastewater sampling can ascertain is that there are (or are not) particular variants, occurring at varying loads within the sample. That can tell you if an outbreak is forming, which is a valuable early warning for any infectious pathogen, but that is the limit of what the surveillance can do.
I was more inclined to think that trying to distinguish variants via sewage is intrinsically flawed, since the Omicron "swarm" for an entire city could have some 157del mutants or otherwise just prompt false-positive. But their previous studies show stark transitions using dels to distinguish Alpha and Delta. Which potentially means the high cycle count isn't as big a flaw either.
RE the model, the math just seems stupid. Delta is staying level until the end. So the model concludes it has to just keep staying level forever, because (as far as I can make out) their equation concludes it will never go high enough to make enough people immune (even though there's tons of prior immunity to Delta). Ok, so your model is idiotic, fix it.
Detecting viral loads in wastewater is a proven concept. The devil of the detail is that the test used has to be of sufficient accuracy and precision to distinguish among potential variants of concern.
That's where the cycle thresholds present a problem--there's considerable evidence to indicate that at higher cycle thresholds (Ct>34 certainly), positive results from viral fragments and dead nucleotides--remnants of prior infection, which are known to linger for quite some time after symptoms have resolved, and can be shed for quite some time after symptoms have resolved.
If the assay is detecting Delta (or Omicron) remnants, the incidence of Delta (or Omicron) is going to be overstated, as the assay was designed to be a quantitative test. Given the fairly recent displacement of Delta by Omicron as the most prevalent variant, including viral fragments in any assessment of the incidence of either variant within a particular population skews the results, possibly dramatically.
That's the other flaw in their modeling--the lack of a discussion about the ratio of "real" cases based on the viral loads found in the wastewater samples and the confirmed cases according to per-patient PCR testing. Without a justifiable ratio estimate to connect wastewater test results to a likely incidence of disease in the community, the only thing the wastewater sampling can ascertain is that there are (or are not) particular variants, occurring at varying loads within the sample. That can tell you if an outbreak is forming, which is a valuable early warning for any infectious pathogen, but that is the limit of what the surveillance can do.