A list over over 150 renowned doctors and scientists requested the World Health Organization to postpone or move the Rio Olympics due to the ongoing Zika outbreak:

[O]ur greater concern is for global health. The Brazilian strain of Zika virus harms health in ways that science has not observed before. An unnecessary risk is posed when 500,000 foreign tourists from all countries attend the Games, potentially acquire that strain, and return home to places where it can become endemic. Should that happen to poor, as-yet unaffected places (e.g., most of South Asia and Africa) the suffering can be great. It is unethical to run the risk, just for Games that could proceed anyway, if postponed and/or moved.  (continue)

However, the World Heath Organization has rejected the request as noted by the BBC:

The World Health Organization (WHO) has rejected a call to move or postpone this summer’s Rio Olympic Games over the Zika outbreak.

It said this would “not significantly alter” the spread of the virus, which is linked to serious birth defects. (link)

However, it appears the W.H.O and I.O.C have not defined “significantly alter”.
In addition to the anticipated violence, and probability of a less than hospitable indigenous rapey-minded population, a foreign visitor to the Olympics now has to worry about contracting an almost unavoidable blood borne pathogen.