The 2 groups are the recently infected and the people who have clinical aids. The 1 in 2500 figure was one I had read and swore by. I belive it applies to people who have past the initial high viral load whose bodies are still strong and suppressing the virus. Only since my infection did I really start looking and reading. I found sites, medical sites which quoted that figure and then asked the retorical question, if HIV is so hard to catch why is it still around. They then answered it by explaing about viral load in newly infected people and people in the later stage, aids. Not sure how they worked it out but the figures I found said the chances of contracting the virus increased by between 26 and 50 times. That brings the 1 in 2500 down to a sobering 1 in 50.
Luck plays its part in all of this, mine ran out sometime in the past 12 months, been doing it over 20 years. Life is for living and you have to be yourself and enjoy it. I may have possibly done things differently had I seen the worst possible scenario odds though, hard to say in hindsight.