Brief Answer:
It can happen that she may test negative- detailed explanations below

Detailed Answer:
Hello and welcome to "Ask a Doctor" service,

There are several factors that determine the risk of HIV transmission. Males are less likely to get the infection compared to women and anal intercourse is riskier than vaginal intercourse. Uncircumcised men are more at risk than circumcised ones. If the woman had her periods or had other concomitant sexually transmitted disease the risk of contracting HIV is increased as well.

The average transmission rate in males is around 0.04% per vaginal intercourse, which means that 4 in 10.000 men having unprotected vaginal intercourse with infected women will contract the infection. Thus, the risk for you to have gotten the infection during that episode of unprotected intercourse is quite low (even though it is a present risk). Blood transfusion, mother to child transmission, needle sharing and receptive anal intercourse consist of the highest rates or transmission.

As for your wife, if you were infected, her risk of contracting HIV is twice as much (8 in 10.000) but still is very low for each vaginal encounter (0.08%). If she receives anal intercourse her risk of contracting HIV increases more than 10 times (it is 1.32% per every anal intercourse). Her risk of contracting HIV from you also depends on the presence of other sexually transmitted diseases, if she has intercourse while on her periods and how often she has intercourse.

It is difficult to calculate an exact percentage, the only exact percentage is that the risk for her to contract HIV if you are infected is 0.08% for each vaginal intercourse and 1.32% in case of anal intercourse, thus regular unprotected intercourse increases the risk and may make it considerable but there is still some chance that she may remain uninfected even if you are infected (and so she may still test negative). She may also test negative if she is recently infected (HIV takes a while to be detected in blood) so she will need to repeat the test in some weeks (depending on the test she had she may need to repeat it again in 3-6 months).


I hope this answers your query and is helpful to you. I remain at your disposal in case further medical assistance is needed.

Regards,
Dr. Antoneta Zotaj,
General and Family Physician

---

Brief Answer:
It is not common but it is possible

Detailed Answer:
Hello and welcome back,

I understand it seems strange that one episode sometimes transmits the infection while numerous encounters don't. As said,vthe risk with one vaginal encounter for men is only 0.04%, this unfortunately, is still not 0.
As for a woman the risk is 0.08% for each vaginal encounter. So if she had intercourse dayly for two years, her risk of contracting the infection is around 60%.
We should not forget this are probability numbers and many times are different from the reality. It is difficult to know who falls in the 0.04% (getting the infection) and who in the 99.06% of those not getting the infection.
As for if this is common, that one episode transmits the infection while several episodes don't- I would say no, it is not common, but it is possible.

I hope this answers your query. I remain at your disposal in case further medical assistance is needed.

Kind regards,
Dr. Antoneta Zotaj, General and Family Physician

---