ph0enixrising

Lots of misinformation here about HIV detection, etc.  As someone who was an HIV educator back home, here are a few facts:

1) If you have a "scare", ie. there was a possible exposure for whatever reason, you should immediately go to a clinic (Pulse, Red Cross, etc.-- your regular doctor may have it as well, depending on the clinic) to get PeP (post-exposure prophylaxis).  This is a pill that contains the same 3 meds in the most common HIV anti-viral medication for those who are HIV+ and should be taken for 28 days.  For this to be effective, you should start within 72 hours of exposure, but sooner is better. Be aware, however, that PeP is not 100% effective.

2) As for when HIV testing can detect the virus, it depends on the type of test:  

Anti-body tests (the most common type) do not actually check for the virus itself but for whether or not your body has created antibodies to fight the virus.  Since it can take up to 3 months for there to be enough antibodies in your bloodstream to be detected, these tests may give false negatives if taken early one (older anti-body tests were not as sensitive, so in the past it could take up to 6 months).  

The two most commonly used tests that detect HIV directly are the p24 antigen test and the HIV nucleic acid amplification test (NAAT). The p24 tests for certain proteins and can give accurate results around 3-4 weeks post exposure.  The NAAT tests for actual dna of the HIV virus and can give accurate results in 7-14 days post exposure.  These tests are more expensive however, so they are not as commonly used.

3) As to getting HIV from a single time with a bar girl (or with anyone for that matter):
On the one hand, it is more difficult that many people think to contract HIV.  The virus is actually very weak outside the body and can be killed with just soap and water.  For someone to become infected, there must be exposure to infected bodily fluids via an "entrance way" into the body/blood stream. 

On the other hand, any small scratch/nick on the skin can be that entrance way. This means that, you probably won't get HIV from a 1 time dalliance... but, it IS possible.  The insertive partner in any sexual encounter is less likely to become infected than the receptive partner... since the normal friction that occurs during intercourse can cause micro-abrasions inside the vagina/anus thus providing "entrance ways" for the virus.  However, any scratch, nick, or cut (even those that are too small to notice) that may be on the penis (or any other body part) can also be an entrance way.

4) With HIV, undetectable=untransmittable.  In other words, even if a person is HIV+, if they are taking their anti-viral meds so that the virus is suppressed and no longer detectable in the bloodstream (anti-bodies will still be detectable however), then that person cannot transmit HIV to another person. 

5) For those who are HIV+, due to the advancements in treatment, as long as one takes their meds, then it's really no different than any other chronic condition (such as diabetes).  With a few minor changes in lifestyle (not drinking too much, getting exercise, etc) the person live a long, healthy life and is far more likely to die of something like heart disease than anything HIV related.

Sorry for the long post... used to be a volunteer counselor/educator for a clinic, so this is kind of the automated answer I used to have to explain to people all the time.