One of the most useful metrics to keep track of how quickly the Covid-19 is spreading in different areas is the incidence rate: the number of new cases in a given period relative to the total population, generally calculated as the number of infections per 100,000 inhabitants over the past 14 days.
It's one of the indicators that the Italian health ministry uses to identify which parts of the country should be placed under tighter restrictions, and it's the main measurement on which the European Union is basing its list of “dark red zones” – coronavirus hotspots around the continent where extra travel restrictions are recommended.
It's important to note that the EU's “dark red zones” aren't the same as Italy's “red zones”, which are classified according to a more comprehensive analysis of different risk factors including the reproduction rate (Rt number), test positivity rate and percentage of hospital beds occupied, among others.
By that complex assessment Italy currently has two high-risk red zones: Sicily and the autonomous province of Bolzano, also known as South Tyrol.
But going by incidence rate, four parts of Italy are potential “dark red zones”: Bolzano province, Emilia-Romagna, Friuli-Venezia Giulia and Veneto.
That's because these areas have a 14-day incidence rate around or above 500 infections per 100,000 inhabitants, the threshold above which the virus is considered to be circulating at a very high level.
Authorities in Bolzano, the only area to appear on both lists, have argued that the incidence rate there appears higher because the province carries out mass screening of asymptomatic residents, resulting in more infections being detected.
“Following this logic a region that didn't do tests wouldn't have any problems, because its incidence rate would be zero,” provincial governor Arno Kompatscher claimed. But Bolzano also shows other warning signs, including a high percentage of tests coming back positive and rising occupancy of hospital beds.
Nationally, Italy's incidence rate is 339.24 new cases per 100,000 inhabitants.
This chart shows the exact incidence rate in each region of Italy over the fortnight ending January 17th, the most recent data that's available from the Higher Health Institute (ISS).
The Italian government has said that regions where the incidence rate drops below 50 cases per 100,000 residents for three weeks straight, among other positive indicators, will be classified “white zones” with only minimal restrictions in place. No region currently comes close to qualifying.
Below you can see each region's total incidence rate since the pandemic began.
The ISS releases new weekly data each Friday, with its next report due on January 29th.
Follow all The Local's coverage of the Covid-19 pandemic in Italy here.