We are roughly eight weeks away from the Olympic Games and a number of people are starting to conclude that the possibility of contracting Zika virus is not worth the risk. The latest is anchor Savannah Guthrie of the Today show, who is pregnant.
I imagine that the decision to avoid Brazil probably did not keep Ms. Guthrie up at night. She is a big-wig over at NBC and, with that status has the ability to call some of her own shots with no repercussions.
But, what if you are struggling with the same decision without the clout that Ms. Guthrie is afforded? What if you are lower down on the work totem pole, and cannot opt out of work commitments without suffering consequences, while at the same time wanting to start a family in the near future? Or, imagine being an athlete who has trained his/her whole life for this opportunity?
How can you find out how likely are you to be infected by Zika if you are one of the half million visitors traveling to the Olympics?
This is a very tough question, but, one that health officials are trying to address. The World Health Organization's Emergency Committee on Zika has scheduled a June 14 meeting to reassess data and review their prior recommendations. But, what type of data are used to estimate the risk?
A new study in Epidemiology and Infection has calculated the risk of contracting Zika. This is how researchers did it:
First, they needed to know (1) the total mosquito population size, and (2) the biting rate of those mosquitoes. With this information in hand, they could then calculate the average number of bites that one person could expect during their time in Brazil. This is called the "man-biting rate" or MBR. Once they had the MBR, they calculated the probability of being bitten by an Aedes aegypti mosquito, during the time spent at the Olympics, to be 3.5 percent (about a 1-in-30 chance).
However, not everyone who gets bitten by a mosquito contracts Zika. So, if you factor into this equation, on top of the probability of being bitten, the virus' "force of infection" — the risk that a susceptible person will become infected with the virus — the risk is reduced to 1 in 31,250. Therefore, getting Zika at the Olympics is less likely than actually becoming an Olympian (as the odds of becoming a professional athlete are 1 in 22,000).
With an estimated 500,000 tourists expected in Brazil for the Olympics, this means, according to the researchers, that the total number of new cases of Zika virus infections will be 16.
What the end result of those 16 new cases will be is even more difficult to predict. Each of those people will travel back to their country and may, or may not, pass it on to others, depending on multiple different factors (ie. whether or not they have unprotected sex.)
So, even though the numbers say that Savannah Guthrie would, almost certainly, not contract Zika while in Brazil, I don't blame her for opting out. She is 44 years old — an age when pregnancy is risky enough, without adding Zika virus to the mix. But, for others who find themselves in a similar quandary as Ms. Guthrie, and cannot opt out as easily, the good news is that the numbers are in their favor.