Coronavirus: key concepts you need to know

Coronavirus: key concepts you need to know

In order to fully understand what is covered in the articles (which you can find by clicking here or at the bottom of the page) we recommend reading the key concepts, listed below.

On the number of new COVID-19 cases, doubts often arise because it seldom is the same as the one provided by Italian Civil Protection. In fact the delta is not real, both the source and the data are the same (the Ministry of Health). What differs is the way they are presented. The Civil Protection publishes data of patients that are “currently positive” as well as the increase/decrease compared to the day before. By “current patients” I refer to all the patients still affected by the active disease, known by the health system and still being treated (regular hospitalization, ICU, at-home isolation). Neither recovered and deceased patients are included. It is quite straightforward that the daily difference of this set of patients is heavely impacted by the number of new cases but also by the number of daily deaths and recoveries that need to be subtracted by the total. If we want to draw conclusions from the strength of the contagion at a given point of time, we only need to focus on the new cases. Including deaths and recoveries is of no help in figuring out the trend. Luckily enough, except for some newscast and websites copy/pasting Civil Protection’s data, the majority of sources report the true new confirmed cases. In the first slide of the file is an infographic that will hopefully be of some support.

The number of new tests undoubtedly influences the number of new positive cases, especially when broad screening campaigns are carried out. Accordingly, many people believe that it should be preferable to “normalize” the counting by scaling the number of new cases by the number of tests. Nevertheless, in the most active stages of the epidemics most tests are performed in the E.R. and a high/low number of tests might just depend on the higher/lower level of access to it. As we cannot rely on the information related to the source of these tests, it is not possible to define a relation with the number of cases and every attempt to normalize might results in the risk of further distort the data.

The real number of infected is surely much different from the one claimed by the official data, nobody knows the exact number. Some think that for every confirmed case there might be somewhat from 4 to 20 times more. Some estimates point to 6 million of potentially infected people in our country. Anyways, the “tip of the iceberg” is sometimes good representation of reality and in this case it allows us to have at least an idea of epidemics’ trend and, especially, of how under pressure the health care system is (inevitably our focus).

The spread of the contagion in Lombardy has generated an outstanding number of serious cases, and such cases required the majority of the tests, performed in the hospitals for the large part. If we had carried out more tests across the region, as did in Veneto, we would have found a way larger number of infected (with mild or no symptoms at all). The percentage of positive tests would be lower and the death rate – the number of deaths out positive cases – would be much more in line with other regions. Having said that, the absolute number of deaths in Lombardy is high and signals how rapid and abrupt the contagion spread across the region and how severely it overwhelmed the health care system. We also need to the add the deaths at home or in the nursing homes to the deaths registered in the hospitals. Only at the end of the contagion it would be possible to determine the death rate, namely the number of deaths divided by the population.

For the epidemic peak , we intend the moment in which the healthcare system is at the maximum patient load: so the number of patients which are being treated or more generally with active disease is at its apex (in our projections the highest point of the yellow curve). We have yet to reach it but it will come, although it’s important to remember that the each region will reach it at different points in time. The peak is reached the moment in which each new infection is offset by someone either being or cured or sadly, passing away, maintaining the total number of cases unchanged. Once the peaked has been passed, it’s at that point that the number of active cases will begin to drop vs. patients who have an outcome. In these days, you also hear a lot about “peak infections”, saying that is has already been surpassed, which is true.
In this case it refers to the in which we experienced the maximum number of new cases (the highest part of the purple portion of the curve). It’s current to speak about the peak in this context as long as one is aware that they are speaking of two different things. The importance of the “peak infections” is that it anticipates the “epidemic peak” by days or weeks and can be extremely difficult to anticipate in the growth phase of the epidemic. Once surpassed, it’s easier to predict the “epidemic peak” with greater accuracy.

Antibody tests measure the immune response against the virus by measuring the antibodies in the blood (unlike nasofarin swabs which looks for traces of the virus in the mucus). Given that antibodies take 2 to 3 weeks to form from the start of the symptoms, this test is effective towards the end of the infection, not in the active stage, allowing one to be able to tell if someone has been exposed in the past to the virus. Rapid fingertip tests and traditional blood tests are available. The latter are seemingly more reliable but the sensitivity and specificity assessements of both tests are still ongoing. The cost and timing of these tests are reasonable and it’s expected that they will be used to screen a wider swath of the population in a short period of time.