In a perfect world, that’s probably true. But here comes a reality check: It’s completely possible for have more than one STD at a time. What’s more, if you already have just one other untreated STD, you are up to 10 times more likely to have HIV. That’s why we always recommend getting checked for STDs, and sooner rather than later.

Reference: http://knowyo.org/the-myths/std-myths