Why does my report have a “not-detected” result when there are reported cases in my area (or the virus has been detected before)?
A result of “non-detect” means the level of SARS-CoV-2 virus genetic material in the influent sample was below our limit of detection. There can be a number of reasons for this. For example, if the number of new infections in your community is small, the virus concentration in your wastewater may hover around our limit of detection.
The location of reported cases can also be a factor. If individuals who have been infected with COVID-19 do not reside in an area connected to your catchment area, then they also will not be represented in the wastewater sample.
Lastly, if the composite sampler is collecting sewage once per hour (vs. every few minutes), fragments of the virus may have evaded the sampling process.
What is your current limit of detection (LOD)?
Our current protocol has a LOD of 4,800 SARS-CoV-2 virus copies / Liter of sewage (4.8 copies/mL). We reliably (>99%) detect the virus when there is at least 1 infected person in a population of 6,500 people. In other words, our methods are sensitive enough to detect even 1 infected person in a community of 6,500 people or smaller.
How should I calculate the change since my last sample or plot my own data?
If you are interested in plotting the data yourself or conducting additional analyses, we highly recommend using the normalized concentration. We have found that normalizing the data to a virus universally found in stool is the best way to control for dilution and variability in sampling. To interpret patterns in your community, we recommend looking at consistent trends across multiple samples, rather than sample-to-sample changes.
Why is my normalized concentration so different from the raw concentration? Should I be concerned?
There is no need to worry if your normalized concentration is different from the raw concentration. That actually should be expected since normalization corrects for any sample dilution.
For example, if your samples tend to be more dilute than the average sample in our dataset, you will see consistently higher normalized values than your raw concentration. That is because the dilution in your samples will lead to lower PMMV levels than average, and so your sample concentrations will be corrected upwards in the normalization process. In fact, normalized concentrations are higher than raw virus concentrations in about half of our samples.
How well does your data reflect COVID-19 cases?
Our dataset shows a consistent correlation between wastewater concentrations and confirmed new COVID-19 cases reported on state and even county levels. For example, our sampling locations' wastewater data accurately reflected both localized peaks in COVID-19 cases last summer (2020), as well as the nationwide surges in late fall 2020 and mid-summer 2021 (spurred by the Delta variant).
What contributes to the variability in the data?
It is worth noting that wastewater sampling yields inherently noisy data. The variability of the data depends on many factors, including: lab processing, catchment population size, and sampling differences.
We are continuously reviewing and improving our lab processes to ensure high-quality data. At the same time, one of the most important factors to improve data quality is the pumping frequency. Therefore, if your data is highly variable, we recommend increasing your pumping frequency to the maximum setting (e.g. pumping every 5 minutes) to mitigate any potential variability from the non-continuous nature of composite sampling.
Do the mRNA vaccines affect our measurement of the virus in wastewater?
No. At this time, there is no risk of mRNA vaccines (such as the Pfizer/BioNTech and Moderna vaccines) affecting the amount of virus detected in wastewater samples. To trigger an immune response, many vaccines put a weakened or inactivated germ into our bodies. Instead, mRNA vaccines teach our cells how to make a protein—or even just a piece of a protein—that triggers an immune response inside our bodies. That immune response produces antibodies, which protect us from infection if the real virus enters our bodies.
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Does your testing detect the new COVID-19 strains?
Biobot testing will indiscriminately detect known SARS-CoV-2 variants. A variant is characterized by one or more signature changes (mutations) to the virus's genetic code (for example, B.1.1.7 has 17 mutations). Similar to standard clinical Covid-19 testing, our testing detects the SARS-CoV-2 virus by targeting the N1 & N2 regions of the genetic code (as designed by the CDC). These two regions are unchanged in the known SARS-CoV-2 variants. Therefore our testing will detect the virus variants (and original variant) all the same.