What's going around in Norway?

FHI integrates sentinel GP consultations, laboratory positivity, hospital and ICU admissions for severe acute respiratory infection, virological characterisation, and active wastewater surveillance into a weekly respiratory-virus picture covering flu, SARS-CoV-2, and RSV. The same indicators feed ECDC ERVISS. On infectrisk.com we condense this picture into a qualitative low/moderate/high classification.

Norway runs an active wastewater surveillance programme at selected treatment plants, measuring viral RNA for SARS-CoV-2, influenza, and RSV. The signal is independent of test-seeking behaviour, which makes it particularly useful when clinical testing volumes drop. Wastewater trends typically lead or co-move with sentinel indicators and help FHI flag rising activity earlier in the season.

Several factors converge in the Norwegian winter. Long, cold, dark months concentrate social contact indoors, where heated air is dry and many respiratory viruses remain stable longer. Schools amplify transmission among children, and holiday gatherings accelerate spread. Immunity to seasonal strains is also typically at its lowest when exposure begins rising after a quiet summer.

FHI uses thresholds derived from historical reference data. Current indicators (sentinel consultations, laboratory positivity, hospitalisation signals, wastewater concentrations) are compared against baselines from past non-epidemic weeks and against reference points from severe past seasons. When several indicators cross into elevated ranges at the same time, weekly bulletins flag activity as high. Norway's ERVISS contribution uses the same framework for cross-country comparison.

Norway's climate, school calendar, and indoor-contact patterns resemble Sweden's and Denmark's, and the three countries' winter respiratory curves typically move broadly in step. Because all report into ECDC ERVISS on the same schedule and methodology, the relative timing and intensity of their peaks is easy to read in the European dashboards. Lead–lag differences are usually a matter of weeks.