Relationship Wastewater / Incidences - Report

Wastewater measurements and Covid incidence - examples

The pandemic is reflected on the one hand in the official test numbers (incidence), on the other hand it can also be mapped using wastewater measurements. In order to illustrate the connection, we show some exemplary graphs for selected catchments:

• Left axis: The course of the wastewater-related measurements
• Right axis: the 14-day incidence.

Wastewater-related measurements:

For the representation and modeling of the wastewater values, the virus load (= total amount of virus particles in the inflow of the sewage treatment plant) in million gene copies per day is related to a population marker. This is used to estimate how many people (population value = PE) the excretions in the wastewater of a sewage treatment plant originate from. This is particularly relevant for communities with a high percentage of the tourist population or with a high proportion of commuters. There are several traditional chemical wastewater parameters (e.g. COD or ammonium) as population markers, which can lead to somewhat different courses of the wastewater signal. The resulting quotient represents a population-related virus load in the wastewater. Its absolute level is secondary, more important is the dynamics of the signal. The points in the graphs indicate the measurement result of a wastewater sample for the respective date. The frequency of the wastewater measurements differs between the systems. The solid line shows the model predictions (smoothing) for the measurement period. The colored corridor shows the statistical uncertainty range of these forecasts.

Two-week incidence in the catchment:

To calculate the 14-day incidence for a sewage treatment plant catchment, the reported positive cases are aggregated according to the Epidemiological Reporting System (EMS) in the municipalities connected to the sewage treatment plant. The daily available 14-day incidence is the total of new cases reported in the last 14 days and is related to the number of inhabitants in the affiliated municipalities (per 100,000 inhabitants) (orange line).
The dashed lines always indicate the beginning of the nationwide lockdown.

Example: City of Salzburg

The black line shows the smoothed course of the sewage signal. This is ahead of the incidence because infected people shed viral particles into the sewage before they develop any symptoms. Depending on the testing strategy in a country, the coverage of infested persons may vary. In some regions, only symptomatic people are tested, in some the testing frequency is much higher. The test results end up in the official databases with a delay of 1-3 days. This lead time for the wastewater-related measurements is estimated at an average of 2-5 days.
This lead time can be seen very clearly in the development of the 2nd wave, which became apparent in September. The sudden increase in SARS-CoV-2 in wastewater in October 2020 is reflected in an almost parallel development in the 14-day incidence.
Furthermore, the trend reversal due to the lockdown at the beginning of November 2020 was first seen in the wastewater, and again with a delay in the incidence. At the same time, the effect of a changed test strategy can be seen from mid-December, i.e. more test-positive cases were found with the so-called mass tests, test roads, etc., which could not be detected in the wastewater to this extent. The renewed increase in mid-February 2021 could again be noted earlier in the wastewater.

The great advantages of pandemic monitoring through wastewater is the observation of the entire population in the catchment area of a sewage treatment plant. In contrast, the sample of the tested population leaves out the unreported number of actually infected people.
Nevertheless, a certain degree of caution in the interpretation must be pointed out here. The wastewater measurement is characterized by fluctuations in the virus concentration, in the dilutions due to rain events and the population marker measurements. This leads to a variability in the measurement results, which can be significantly reduced by increasing the sample frequency.
Another uncertainty factor is the occurrence of virus mutations with higher viral loads in the body with possibly increased virus excretion into the sewage system.

Example Vienna:

With the main sewage treatment plant in Simmering, we have the special case that one plant covers an entire city. The increase in the incidence in late summer 2020 could also be seen in the wastewater, but not so clearly due to the later dynamic development. Nevertheless, the sudden growth during the second wave was observed earlier and very clearly in the wastewater signal. As in the example of Salzburg, the delayed braking effect of the November lockdown can be seen in the wastewater. Particularly noticeable is the early rise in the sewage signal as early as mid-January, when the 14-day incidence was still falling and rising significantly with a delay.

Example sewage treatment plant Wörthersee-West (Carinthia):

With around 24,000 people, this facility has a smaller catchment area, but due to towns such as Velden, there is a seasonally high tourist traffic. The temporal progression patterns are very similar to the examples already described. Here, too, it appears essential that the trend reversal in the infection process in the wastewater became apparent at the end of January 2021.



Aberi P, Arabzadeh R, Insam H, Markt R, Mayr M, Kreuzinger N, Rauch W. Quest for Optimal Regression Models in SARS-CoV-2 Wastewater Based Epidemiology.
International Journal of Environmental Research and Public Health. 2021; 18(20):10778.
doi: https://doi.org/10.3390/ijerph182010778

Arabzadeh R, Grünbacher DM, Insam H, Kreuzinger N, Markt R, Rauch W; Data filtering methods for SARS-CoV-2 wastewater surveillance.
Water Sci Technol, 2021; 84 (6): 1324–1339.
doi: https://doi.org/10.2166/wst.2021.343

Markt R, Mayr M, Peer E, Wagner AO, Lackner N, Insam H. Detection and Stability of SARS-CoV-2 Fragments in Wastewater: Impact of Storage Temperature.
Pathogens. 2021; 10(9):1215.
doi: https://doi.org/10.3390/pathogens10091215

Rauch W, Arabzadeh R, Grünbacher D, Insam H, Markt R, Scheffknecht C, Kreuzinger N. Datenbehandlung in der SARS-CoV-2-Abwasserepidemiologie.
KA - Korrespondenz Abwasser, 68 (2021), 7; 547- 554.