Although the odds of contracting an STD through daty is small, it isn't zero.  All the more reason to do your homework and try and stick to the ladies that do their homework and take care of themselves.  There are lots of Vegas Ladies that take excellent care of themselves including medical visits to make sure about their health.  Although not 100% fool proof you can often tell by reviews which ladies are more likely to contract something based on the things they do during an engagement.  Stick to the ladies that do everything covered and don't swallow anything as a rule of thumb to minimize the paranoia level.  And for God's sake don't go down on a bar crawler that's offering anything for $150.