I am a great fan of Dan Brown. I have read all of his books and enjoyed every single one of them! Great fiction and storytelling. Most of all, I always admired Brown's capacity to fuse fantastic elements with actual historical or scientific facts. This is why I decided to test one of my favorite of his books, Inferno.

Before we proceed, a warning for all those who have not yet read the book and wish to: the following paragraphs contain SPOILERS unveiling some of the mysteries of the book.

The Inferno Infection story

In the story, a crazy scientist is supposed to have planted an infectious virus in the Sunken Palace, a popular touristic destination near Hagia Sophia in Istanbul, attracting more than five thousand visitors every day. To make things even worse, the wealthy scientist has arranged, by an anonymous donation, for a classical concert to be hosted at the Sunken Palace for seven consecutive days, thus increasing the number of visitors even more. His plan is simple. During this special seven-day period, he aims to infect all visitors with this highly contagious airborne virus. Since Istanbul is a tourist destination from literally everywhere in the world, the infected visitors, when leaving this place, could go anywhere from Istanbul to back to their homes, thus spreading the virus around the globe quickly.

The bold claim

But how quickly can a few thousand people infect the whole planet of 7 billion souls? Well, according to the book, just seven days should suffice!

That’s quite a bold claim, so I decided to put it to the test by using the IS model. This model can be used to simulate interaction processes in general, in this case, a contagion triggered by the aforementioned Istanbul Sunken Palace infection.

The simulation

Without getting too much into the details, the total number of infections each day, according to the IS model, is influenced by two things:

(a) the seven days “feed” of infections from the Sunken Palace. We know this to be at least 5000 infections per day

(b) the probability of contamination between any possible combination of Infected and not Infected-normal people around the world. This is more difficult to find, but we can calculate it to be approximately 0.0000002% per day (see note* for key assumptions).

This is all we need to construct the model and make the simulation. The resulting graph showing the evolution of the Infected (red bars) and Non-Infected (blue bars) people around the world is shocking!

The verdict

Brown got it right!

Impossible as it may seem, the whole world could indeed be contaminated within only a week under the exact conditions described by Dan Brown in Inferno. Actually, and even more surprisingly, the result would be the same for even looser assumptions. According to the IS model simulation, for any number of visitors over 650 per day, even one day would suffice to contaminate the whole living population of the Earth within a week…

A real threat?

So, is this what it takes to make our world disappear, a lunatic clever enough to hide a dangerous biological agent inside any great touristic attraction in the world?

Well, to bring panic levels down, it’s not that simple at all, for two reasons. First, an airborne virus that is almost 100% contagious, as described in the book, does not exist today. And second, and more importantly, the Inferno virus causes sterilization and has no symptoms at all. Hence, it goes undetected as the epidemic grows, without any counteraction to contain it. This is not the case though for most epidemics, as there are visible symptoms and, possibly, deaths that trigger alarms on a local or international level as it happened, for instance, with the recent Ebola epidemic that was eventually successfully contained.

Epilogue

So, we can continue to read sophisticated fiction, like the one Dan Brown writes, enjoying the clever fusion of facts and fantasy without the fear of this becoming a reality. However, in my mind, Brown‘s book, apart from being excellent fiction, also serves as a wake-up call, alerting us about the possible pitfalls of our modern globalized society, as the continuously evolving technology can bring us closer to each other, for better or for worse…

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* Key assumptions for calculating the probability of infection:

Infected visitors from the Sunken Palace leave Istanbul every day and travel practically everywhere around the world. The total number of buildings in the world is approximately 1 billion. Each person of the 7 billion that populate the Earth, either infected or not, resides or visits any of these buildings with a probability of 1 in a billion. So, the probability for a certain infected person to meet a non-infected person in a certain building and pass the virus is 1 to 1 billion x 1 to 1 billion (for those of you familiar with basic probability theory, this is obvious, for all others please google it or just take my word for it!). Since this may take place in any building in the world, we have to multiply this probability by the total number of buildings i.e. 1 billion. Moreover, it’s common sense that every person makes at least two visits per day, one inside its private residence and one outside, either to work, visit a friend, or perhaps buy something, so we also have to multiply by 2. Combining all the above, the probability of an infection for any of the possible combinations of infected and non-infected people is 2 out of 1 billion (0.0000002%) per day.

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