Every year, pathogens borne by faeces-contaminated water cause hundreds of thousands of deaths globally. Climate change is expected to worsen water quality, including in the Nordic countries. Identifying the sources of faecal contamination is important to reliably assess related health risks and keep faeces out of waterways.
Genetic markers reveal the source of faecal contamination
A study by Annastiina Rytkönen introduced in Finland a method based on genetic markers for identifying faecal contamination sources in surface waters. These markers identify a small sequence of the genome of intestinal microbes typical to specific animal species, or the animal’s own genome from intestinal cells that have passed through along with the faeces. This identification method can be used to infer the host animals of intestinal microbes detected in water samples. The method can distinguish between wastewater from human and animal sources such as cattle and birds.
In her study, Rytkönen employed ribosomal RNA (rRNA) molecules abundant in active microbial cells to improve the method’s accuracy. The sequences of the intestinal microbial genome detected by the genetic markers are replicated to these molecules. The abundance of rRNA molecules helps the markers, as microbes are diluted in surface water.
Norovirus from sewage, campylobacteria from farms
The study found both human faecal markers and norovirus in waterways close to wastewater treatment plants. When assessing the risk of waterborne infections on bathing beaches close to these plants, the risk of norovirus infection was found to be markedly elevated when wastewater loads were higher than usual.
In contrast, ruminant- and avian-specific faecal markers were found, together with campylobacteria, in waterways located near cattle and sheep pastures. However, the infection risk caused by animal faecal contamination on beaches close to pastures turned out to be considerably lower overall than the risk posed by wastewater.
Method helps target water conservation measures
The method introduced in the doctoral thesis can be used to identify microbiological risks to waterways and target water conservation measures at contamination sources that, based on tracking, are decreasing water quality. It can be used, for example, to support official monitoring at beaches should bathing water quality decline and the reasons require investigation.
The doctoral thesis was written in the Doctoral Programme in Food Chain and Health at the Department of Food Hygiene and Environmental Health, University of Helsinki. Collaboration partners included the Finnish Institute for Health and Welfare, Natural Resources Institute Finland and the Häme University of Applied Sciences.
Information about the doctoral thesis
Annastiina Rytkönen, MSc, will defend her doctoral thesis entitled ‘Hygienic surface water quality in proximity to faecal contamination sources – Application of modern molecular methods in water quality evaluations’ on 8 May 2026 at 12.00 at the Faculty of Veterinary Medicine, University of Helsinki. The public examination will be held in room PIII of the Porthania building (Yliopistonkatu 3) at the University’s City Centre Campus. The event can also be followed over a
The thesis is also available in electronic form through the