Hi,
If I'm correct there are at least 3 different tests for finding HIV antibodies. You might ask her doctor how strongly the test that showed her positive was. It is possible to get a false positive on one test, but if the others all show negative then it probably was a mix up at the lab or else the vial of blood sat somewhere to long before they could test it which caused a false reading. I had a viral load test that sat at an airport a couple of summers ago in the heat and the test came back showing a viral load of 600,000. I retook the test and it was undetectable. So mistakes can and do happen. Also, it is possible for the virus to be hiding in the bone marrow which can make it hard to find (this usually is with a recent exposure to the virus). Her doctor should have recommended her to test again in 6 months. Did they ask your mom when they did the blood work 4 months ago if they could test her for HIV? When blood work is done they will tell you that they are doing a complete blood test, but they have to have the persons permission to do an HIV test. Many people get confused by this and think that they've been tested for HIV when they have not.
Don't panic though, wait and see how the rest of the tests show up and get your mom to test again in 6 months just for some peace of mind. If she is in a high risk for exposure she should get tested every year as well.
The Viral Load test gives a quite accurate showing of how much active virus is in a persons blood. However, the amount of virus in the lymph nodes and brain (places where it can hide) can be much higher but not active in the blood. It is still under control in this case but you can still infect someone and you can still get sick if you stop your HIV medications or the virus becomes resistant to the medication.
I found out I was HIV+ in 1997 because I had been fighting Sinusitis all summer and treatment wasn't working. So the doctor asked me to have an HIV test. I did and it was positive (all 3 tests which they did at the same time) the test was positive without question they told me. When I had my first viral load test it was 200,000 so there was alot of virus in my body and that explains why they were so certain of me being positive, because they would have found high numbers of HIV antibodies in those 3 tests since my virus was so active. At the time I found out I was positive I had full blown AIDS. I didn't know that until a couple of weeks later when the viral load test came back. And my sinusitis wasn't just sinusitis but PCP so I was hospitalized for 8 days and then went through a month of chemo treatments to cure the PCP. I had my testing done though the local health dept., so I wouldn't have to pay for the tests.
It can take 10 or more years to develop AIDS. My doctor told me it takes at least five years in the worst case to develop AIDS in her opinion. During those years most people don't have any clue that they are HIV+ (that's why testing is important). Most folks don't get sick till they have full blown AIDS. You do get a mild flu like symptoms a few weeks to months after you get infected, but I like many didn't think anything of it. Of course, for me that happened in 1984, after that I wasn't sick except for colds till 1997. In 1984, everyone thought if you got AIDS it was fast and you didn't recover from any illnesses you developed and that you died quickly. It took a number of years for that to be found out. In 1984 HIV was a new term it had been called HTLV and there wasn't a true test for the antibodies. What they tested for was Hep., B antibodies because alot of people with Hep., B also would get and develop AIDS. This is why so many false tests were done back then. They figured it was a virus but they hadn't found the virus at that time.
I hope this answers your questions if not feel free to ask me more.
Mark