Odds of infection?

I have read some strange statistics that say the Odds of catching HIV from a one-off, unprotected encounter with an HIV-positive person is somewhere between 1/500 to 1/1000..is this accurate?

[Dr Jose]

It all depends on the specific type of encounter. If you are a man having penetrative vaginal intercourse with an HIV positive woman, the risk of one single encounter, unprotected would be around 0.1% (1 in 1000). However if you are a man or a woman, receiving anal sex, unprotected, by an HIV positive man, the risk is much higher, around 3% (1 in 33).
Best wishes,
Jose

Thanks for this. One further question, are there any other factors? I mean, if the act only laster 30 seconds, and neither party climaxed, does this make any difference?

[Dr Jose]

Yes, of course, but that is much more difficult to calculate.
All the best,
Jose