Each country is coloured by how its most recent ILI/ARI rate compares to its own history for the same week of the year — not to the raw numbers other countries report. The five bands (very low → very high) share the ERVISS band names but are locally computed percentiles, not MEM thresholds.
The ERVISS feed mixes two denominators: some countries report per 100 000 population, others per 100 000 consultations. Same disease, same week, no flag in the file to tell them apart — Austria's 2817 and Iceland's 5.5 are not on the same scale. Banding each country against itself sidesteps this.
ILI is heavily seasonal, so a plain all-history percentile would just paint the map by month. The bands here compare against the same ISO week in each of the previous 5 seasons — answering "is this week high for this time of year?".
The 5-year cap is deliberate: it excludes the acute COVID period whose disruption to consultation patterns would flatten the bands. As older ERVISS data accumulates the cap will start to bite; today most countries have 2–4 seasons available.
The band says the current value is unusually high for that country at that week. It cannot distinguish a genuine surge from a change in how that country counts (denominator switch, sentinel-network change, reporting-cadence shift). Treat a lone very-high country as a signal to check the source, not as a comparative claim against its neighbours.
As a partial safeguard, values that sit well beyond the country's own historical range for the same week (more than ~2.5× its 98th-percentile) are treated as likely source-side artefacts and greyed rather than banded very-high.
Source: EU-ECDC ERVISS weekly data. Bands are computed by this site's extractor; see the JSON's band_config field for the exact thresholds.
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