which diseases are the most contagious or the most deadly?

By Pierre Breteau

Posted today at 1:02 p.m., updated at 1:39 p.m.

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The 2019-nCov coronavirus, which appeared in December, has already killed around 100 people in China and caused worldwide concern. Is this virus particularly dangerous?

According to the World Health Organization (WHO), the 2019-nCov death rate is 3%, well below that of severe acute respiratory syndrome (SARS) – with a death rate of 9.6% , it had made 774 victims in 2003, always according to the WHO.

2019-nCov, which is transmitted by air, also has a relatively moderate contagiousness index – 2.4 against 17.6 for the rotavirus responsible for gastroenteritis.

The table below represents around forty of the most frequent viral, bacterial or parasitic diseases, classified according to these two criteria:

• the ease of transmission between human beings (contagiousness, or R₀, virus reproduction rate);
• the proportion of infected patients who die from it (mortality rate).

However, it does not take into account other factors, such as the number of people affected or the medical response.

The list of diseases that are not very contagious but have a high mortality rate are not that long: there is Ebola fever (with 50% mortality and a contagiousness comparable to that of the seasonal flu) or rabies when it is not treated (100% mortality). Tuberculosis presents a particularly threatening profile with both high contagiousness and a high mortality rate, even if living conditions and hygiene weigh heavily on the risk for different populations.