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Ivan Romano via Getty Images
These days there is a feverish discussion about the criteria with which the Regions are declared lower risk areas and there are Regions that protest, claiming that they have been evaluated too harshly. Rather, it should be considered that some have been evaluated too optimistically. However, to realize this, we must have a good understanding of how these zoning works.
President Conte affirmed that the 21 indicators on which the decisions about the color assigned to the Regions depend (red, yellow, orange or green zone) must be “absolutely accessible”. “The confrontation must take place – he said – as well as with the scientific community, with citizens, who are currently outside this system.”
While waiting – hopefully brief – for a government communication that implements this purpose, it would be desirable for the Regions themselves, which since last May have collected and communicated local data for the 21 indicators to the Government, make them public, also adding the relative indicators . to individual provinces, in order to objectively evaluate the opportunity for differentiated containment measures at the regional level.
From many points of view it has been emphasized that perhaps the most important parameter, the one that gives us the crucial information on epidemic growth, is Rt, as Walter Ricciardi has also recently repeated. A value of Rt greater than 1 implies exponential growth: the higher Rt, the faster this growth will be. However, in order to confront citizens on these issues, it is absolutely necessary to make them understand what this Rt index is, what it means, how it is calculated and if its calculation is reliable.
Simplifying as much as possible, the Rt value indicates to what extent new infections have increased or decreased during the week:
• If Rt is equal to 2, the number of new infected doubles in a week.
• If Rt is equal to half, the number of new infected halves in a week.
• If Rt is exactly equal to 1, the number of new infected remains constant.
A value of Rt greater than 1 is, therefore, unsustainable in the long term: it corresponds to exponential growth, more or less rapid. Therefore, it is essential to reach a situation of Rt less than or equal to 1. To give an example, during the spring blockade, Rt was slightly less than 0.7, a value that corresponds to halving the new infected in about a dozen days.
But how is Rt calculated? It is not an easy task, because we do not know exactly when people were infected. One might naively think that to calculate Rt it is enough to know how many new positives there are, a number that is announced daily in all the media.
Contrary to what the man in the street may think, to calculate the contagion curve it is preferred to count the daily number of people who have experienced symptoms. In other words, if the number of people who have had symptoms in the second week of October is double that in the first week, Rt is 2. Epidemiologists make this decision to measure growth because it gives more reliable results (it does not depend on the number of swabs performed), but obviously this requires that the date on which the singles tested positive felt the first symptoms be recorded and that this information be transmitted to the Istituto Superiore di Sanità.
Unfortunately, there are Regions that regularly transmit this data, and others that do so in an extremely limited way: for example, from the beginning of the epidemic, the number of people whose date of onset of symptoms is known is 50% of cases positive in Lazio, while the same proportion falls to 15% in the case of Campania. Therefore, Campania in the vast majority of cases does not convey this crucial information.
Giorgio Parisi
To realize this visually, just look at these two graphs: Lazio on the left and Campania on the right: the light color represents the number of positive cases registered in one day, while the dark color represents the number of people who have experienced the first symptoms that day. It can be seen with the naked eye that the proportion of cases with an onset date in Campania is approximately one fifth of that in Lazio. It is not necessary to know the absolute number of cases: just look at the relationship between the area of the light green area (approximately the same in the two Regions) and the area of the dark green region (extremely smaller in Campania).
Therefore, since Campania, in at least 80% of the cases, does not transmit information about when the symptoms occurred in Campania to the Istituto Superiore di Sanità, any estimation of the Rt value with the standard methodology is absolutely unreliable and the valuation Rt’s ending that appears in the media is absolutely arbitrary.
In the decree of the Ministry of Health of April 30 (the one that had introduced the indicators), the possibility that the Regions did not transmit the fundamental data for evaluation had been correctly considered. In fact, after having given the specifications of the indicators, he added: “If an evaluation according to the methods described is not possible, it will constitute in itself a high-risk evaluation, since it is descriptive of a situation that cannot be evaluated. and consequently potentially uncontrolled and not manageable. ” These wise words, which are repeated obsessively in hundreds of regional ordinances, have a unique meaning: Regions that do not communicate essential data automatically have a high-risk assessment. So there really is no time to waste yet, we must finally move from words to deeds.
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