I'm interested in this as well as far as the risk for a top. I've fucked guys who claimed they were negative, though I'm well aware that some are probably lying (not accusing them, but I'm aware they exist). Haven't gone as far as fucking poz undetectable guys, but I'm interested in doing this potentially and crossing the border (consciously). Would be nice to have someone to take the plunge with me.
I know this is ultra technical, but it probably doesn't hurt to apply some statistical analyses to this. According to the CDC, the relative risk for a top getting infected by a bottom who is positive (this is an average- and assuming not poz undetectable- poz undetectable guys have significantly lower viral loads than those who are unmedicated) is 6.5/10000, for a one-time exposure. You can assume a binomial distribution model for this, where you can determine the probability of an event occurring after multiple events. In this case, it's getting infected, so let's assume a 1 time success rate (of getting infected) out of 1000 trials or exposures.
The formula for this requires some lengthy mathematics (simple for a guy who's familiar with factorials and whatnot- the formula's in Wikipedia), but we can simplify it to 1000*(6.5/10000)*(1-6.5/10000)^(1000-1). This comes down to roughly 0.339, or having a 34% probability of becoming HIV positive.
In simple English, if you fuck (as a top) 1000 times with HIV positive guys (assuming not on meds, as opposed to those on meds), you have a 34% chance. If you fuck 500 times, you have a 23.5% chance. 400 times- 20%. 300 times-16%. 200 times- 11%. 100 times- 6%. 10 times- 0.65%.
Now, I'm not saying that this is an accurate model, but I thought some number crunching would give somewhat of a picture.
