Of course its low, but its still something that needs to be considered as more and more commercial organizations gain the ability to launch things into our solar system. Obviously an organization like SpaceX has a commercial focus rather than a scientific one like NASA. The more stuff gets launched by more people the more likely of contamination from something.

Between SpaceX, Blue Origin or any other space travel initiatives that end up succeeding we are going to end up with a lot more stuff in space which isn't necessarily going to be friendly to scientific efforts as in the past.