Like everyone else in the world, I’m following the news about the spread of the SARS-CoV-2 coronavirus and associated Covid-19 disease and have thus been bombarded by the words that accompany a pandemic; words like self-isolation, social distancing, incubation period, quarantine, infection, hand gel, face mask, herd immunity, stockpiling, event cancellations, underlying health reasons, front line, travel restrictions and closure of borders, shops, restaurants, and places of entertainment. I’ve also been tracking the social impact of the pandemic and I recalled a movie made in 2011 called Contagion that was a dramatisation of what might happen if an unknown and deadly new virus was suddenly unleashed upon an unsuspecting population. The film, directed by Steven Soderbergh (Sex, Lies and Videotape, Erin Brokovich, Traffic, Ocean’s Eleven/Twelve/Thirteen…) boasts a star-studded cast and was highly praised at the time of its release for its attention to scientific detail and accuracy and depiction of what might happen to society as scientists race to find a vaccine before the death rate starts to wipe out whole populations.
I watched the movie when it first came out in 2011 and, this morning, watched it again. It’s a great movie and I see that it’s trending on Amazon Prime, YouTube and Hulu. If you’ve not seen it, I recommend it to you so that you can compare it with what is happening with the SARS-CoV-2 coronavirus, and also learn from the technical detail. I’ll not go into details about the movie’s story but here is Rotten Tomatoes’ synopsis:
Contagion follows the rapid progress of a lethal airborne virus that kills within days. As the fast-moving epidemic grows, the worldwide medical community races to find a cure and control the panic that spreads faster than the virus itself. At the same time, ordinary people struggle to survive in a society coming apart.
With stars like Kate Winslet, Matt Damon, Marion Cotillard, Laurence Fishburne, Gwyneth Paltrow, Jude Law, and more, the movie just zings along with multiple story lines and realistic depictions of events. In the movie, you will find scenes of empty supermarket shelves, deserted airports, martial law, border patrols, mass hysteria and other law and order breakdowns, health screening, deep cleaning, makeshift hospitals, food handouts – some of which scenes we are now witnessing in the daily news. But two medical terms – fomites and R-Naught – and a statement about the frequency of face touching caught my attention. Here’s a brief explanation.
Fomite and Face-Touching Frequency
During the film at around the 18-minute mark, Kate Winslet’s character, Dr Erin Mears, an Epidemic Intelligence Service officer, has a meeting with some officials in a Health Department in Minnesota. At the start of the meeting, she mentions fomites:
A formal definition of fomites is as follows: A fomes or fomite is any inanimate object that, when contaminated with or exposed to infectious agents, can transfer disease to a new host. (Wikipedia’s definition)
We are being urged to wash our hands frequently to reduce the possibility of carrying the coronavirus from our hands to a point of entry on the face (mouth, nose or eyes). If we have picked up the virus through contact with a contaminated surface, then that surface has become a fomite.
Dr Mears then states that the average person touches their face between 2,000 and 3,000 times/day and adds that this equates to 3 to 5 times every waking minute.
I checked the maths behind these statements. Assuming 16 waking hours/day which equals 960 minutes/day, 2,000 face touches averages 2.08 touches/minute and 3,000 touches averages 3.12 touches/minute. Something’s not right. Where have the 3 to 5 times every waking minute figures come from? Maybe the 2,000/3,000 figures are wrong, or my figure of 16 waking hours is incorrect. I tried fact checking. I entered “How many times does a person touch their face during a day?” into Google and came up with a wide spectrum of answers, some based on Dr Mears’ statement above, some based on scientific research, and some just speculation and rough estimates. I don’t know the correct answer but this scene in the film made me think about the fomite-to-face transfer risk and made me conscious of how often, when and why I touch my own face. It’s quite often!
Dr Mears then introduces the virus reproduction ratio, R(0), pronounced R-Naught. R-Naught defines the average number of people who can be expected to become infected by one person carrying the virus. As you see from the captured screenshot above, someone with the flu virus can be expected to infect one other person; someone with smallpox, three people; and polio, before an effective vaccine was developed, four to six people. The higher the R-Naught figure, the more virulent the virus.
This piqued my curiosity. What is the calculated or predicted R-Naught figure for SARS-CoV-2? One result I found, published 10th March 2020, states R-Naught for this virus is estimated to be 2.2 – that is, two people at least will be infected by someone carrying the virus. This is frightening. In simple terms, one infected person (1 infected person, Patient Zero) can infect two people (2 more infected people), each of whom can infect two more people (4 more infected people), each of whom can infect two more people (8 more infected people), each of whom… In mathematical terms, this is the geometric progression of 1, 2, 4, 8, 16, 32, 64, … Do you remember the chessboard and grain of rice story? “I’ll have one grain of rice on the first square, two on the second, four on the third, eight on the fourth, and so on, continuously doubling up until you reach the sixty-fourth square.” If so, you might recall that the total number of grains of rice on the last square was in the vicinity of 9.22 quintillion (9.22 x 1018, strictly 263). That’s a lot of rice!
(If geometric progressions fascinate you, what is the total number of grains of rice on the 64 squares of the chessboard? The answer, maybe surprisingly, is double the number on the 64th square minus one grain i.e. around 18.44 quintillion or more accurately, 264 – 1. That’s an even bigger bag of rice!)
If you are interested to see what the R-Naught figures are for a variety of infectious viruses, look at Wikipedia’s article here. Airborne measles has the highest R-Naught at somewhere between 12 and 18. Don’t go anywhere near someone with measles unless you have been vaccinated.
Contagion is a great movie and I recommend it to you but please resist the urge to scratch your nose, pick your teeth, or rub your eyes, or, alternatively, rub your eyes, scratch your teeth, or pick your nose while watching.