As containment measures gradually loosen, in the last period, we're seeing an increase in cases and, to a lesser extent, of the hospitalizations.
Many, unfortunately also listed doctors, claim and claim that the new cases are all or almost asymptomatic, alluding to a non-relevance of the problem. There are those who launch themselves and in interviews with national newspapers say that the 90% of the new cases is asymptomatic.
The problem is that so many citizens who are furious to hear these statements made by doctors and politicians are convinced that they are true.
Let's see what the real numbers are, those declared by the Istituto Superiore di Sanità, if they are consistent and what conclusions can be made.
Let's analyze the official report updated to the 18/8 and published on 21/8 https://www.epicentro.iss.it/coronavirus/bollettino/Bollettino-sorveglianza-integrata-COVID-19_18-agosto-2020.pdf
The ISS publishes the date of onset of symptoms for cases diagnosed by the 3 per 16 August, data available for 2312 on 5813 cases.
This means that at least the 40% of the cases it is symptomatic and the asymptomatic are at most the 60%.
This figure is consistent with the one shown in the graph that I attach (figure 16) of stratification by gravity at diagnosis.
60% it is very different from “All” or from 90%
So the asymptomatics are the 60%?
I used the wording “maximum” because the figure of the figure 16 refers to the situation at the time of diagnosis. Many cases are now identified at an extremely early stage and therefore may still be in the incubation phase and present symptoms later.
We have another source where we can grasp the severity of new cases: the WEB INFOGRAPHIC OF THE ISS updated daily (https://www.epicentro.iss.it/coronavirus/sars-cov-2-dashboard)
Here is reported the current severity of cases diagnosed in the last month, stratified by age group. As you can see, although the asymptomatics are several, are not the 90%.
This graphic indicates the current status, therefore among those that are indicated as asymptomatic, both incubating and clinically cured cases may be present, waiting for the double negative swab.
Why so many asymptomatics?
It has been known for months that asymptomatics represent an important share of cases, which is estimated in the 26-38% (https://www.medrxiv.org/content/10.1101/2020.04.25.20079103v3.full.pdf+html)
Why are we finding the 50-60%?
There are three explanations:
-the first, as I said, is that some of the new diagnoses are subjects in incubation who will manifest symptoms later.
-the second is linked to the fact that today they are infecting mainly young people as demonstrated by the average age of cases lower than that of the population (32 Vs 45 years). In younger people, milder forms and a higher share of asymptomatics are expected.
-the third explanation is related to the intrinsic limitations of the test: the search for sarscov2 by PCR is a very very specific examination, i.e. there is a very low probability that the test will be positive in an unfected subject. But this probability is not zero and testing many people false positives can be a not negligible number. The specificity of the swab is greater than the 99,75% as demonstrated by the very low percentage of positive swabs in June-July (The 12/6 were positive 0,23% of 70620 Swabs) If we test today 70000 people a day it is possible that, maximum, 100-150 cases a day are false positives and therefore that a part of the subjects declared asymptomatic are actually false positives.
Real false positives may be less than 100-150 per day on 70000 Swabs, given that the real specificity of the swab could be higher than the 99,75%. With a specificity of the 99,9% false positives are reduced to a few dozen a day.
Summarizing: asymptomatics are today a relevant percentage both for the characteristics of sarscov2 infection, both for a low average age, both for a low but not insignificant share of false positives.
Cases are increasing but the symptomatic and asymptomatic ratio is roughly the same, as reported by the ISS and as confirmed by the growing number of hospitalizations, so the symptomatic are also increasing.
An increase in cases should not be underestimated. The cure or vaccine will not come soon, if cases increase (and they do it exponentially), sooner or later you will find yourself in difficulty again.
You have to be strict in distancing, in the use of masks and hygiene measures to reduce infections.
