Thank you for your post and welcome to our forum. I will try to answer each of your questions here below:
1.) That is correct. However HIV RNA is already detectable at 7 days with a high level of reliability of around 99%.
2.) Our lab gives us figures of an accuracy of 99% at 7 days.
3.) We follow UK guidelines. At 7 days, it has an estimated reliability of 99%, which increases with time and after 10 days, this would be over 99%. If we combine this with a relatively low risk sexual encounter like yours, we could consider a negative result to be conclusive. However current UK guidelines would still recommend a follow-up HIV Duo test affter 4 weeks, even though in practical terms this might not be necessary.
4.) The estimated risk of a heterosexual man having unprotected vaginal intercourse with a known HIV positive woman is less than 1 in 1,000. If the status of the lady is unknown and this is in the UK, this will be less than 1 in 1 million as there are only about 40,000 women who are positive in this country.