The data presented on this page were generated in the SLU (Swedish University of Agricultural Sciences) laboratories of SEEC (Swedish Environmental Epidemiology Center). The project was part of SciLifeLab's Pandemic Laboratory Preparedness (PLP) Program and was led by Anna J. Székely at the Department of Aquatic Sciences and Assessment, SLU. Wastewater analyses were overseen by Anna J. Székely, Javier Vargas, and Maja Malmberg at the Virology Unit of the Department of Biomedical Sciences and Veterinary Public Health, SLU.

This page presents historic measurements of influenza A and B virus levels in multiple cities across Sweden. The project had the broadest geographic coverage in Sweden and generated data covering 43% of the Swedish population.

The data and visualisations are no longer updated. The values in the dataset and plots are final, although minor corrections may have been applied retrospectively. This dashboard records the project's results during its active monitoring period.

Wastewater collection sites

SLU-SEEC collected and analysed samples for influenza A and B viruses from multiple areas. The table below lists each town or city, the wastewater treatment plant (WWTP), the estimated catchment population, and the monitoring start and end dates.

The start date is the first influenza A measurement; influenza B monitoring always began later. A missing end date means that collection was still ongoing when this historic table was generated. An asterisk after the population indicates a BOD7 estimate of the connected population. Two asterisks after a town or city indicate that only influenza A data are available.

Visualisations

Important: Although the same methods were used for all cities shown, differences in wastewater collection systems and populations may bias direct comparisons between cities.

Influenza A

Influenza B

Dataset

The data underlying the influenza A and B visualisations can be downloaded using the links beneath the plots. Influenza A data are available from week 42 of 2022 and influenza B data from week 12 of 2023, with final data from week 39 of 2024.

Contacts: anna.szekely@slu.se and javier.vargas@slu.se

How to cite the dataset

Székely, A. J., Malmberg, M., Vargas, J., Mohamed, N., Dafalla, I., Petrini, F., and Davies, L. (2023). Dataset of SARS-CoV-2, influenza A and influenza B virus content in wastewater samples from wastewater treatment plants in Sweden. https://doi.org/10.17044/scilifelab.14256317.

Methods

For most cities represented on this page, raw, untreated wastewater samples representing a single day were collected by flow-compensated samplers at wastewater treatment plants. Uppsala was the exception: samples were collected daily and combined in proportion to flow into one weekly composite sample for analysis.

Viral genomic material was extracted from fresh samples using the direct-capture method with the Maxwell RSC Enviro TNA kit (Promega).

Influenza A and B genome copy numbers were quantified by one-step RT-qPCR using the Flu SC2 Multiplex Assay from the Centers for Disease Control and Prevention. To correct for differences in population size and wastewater flow, pepper mild mottle virus (PMMoV) was quantified using a modified version of the assay by Zhang et al. (2006). PMMoV is abundant in human faeces and serves as an estimator of faecal content (Symonds et al., 2019).

Values in the graphs and data file represent the ratio of influenza A or B copy numbers measured by the Flu SC2 Multiplex Assay to PMMoV copy numbers, multiplied by 1,000. Because the influenza assay estimates virus content and PMMoV estimates faecal content associated with the contributing population, this ratio can serve as a proxy for influenza prevalence in each wastewater catchment.