I definitely believe this was deliberate - false positives are rare, especially with modern tests. If there is a false positive, you will do a repeat test and a confirmatory test on the same sample - there is no need to inform the patient, unless there was something wrong with the sample and you need to get more blood. If this was a doctor, his behaviour was totally unethical and would go against all standards of care we would have in the UK
Well it's perhaps slightly more complicated that that. It comes down to questions of sensitivity and specificity (as it does with Luminol and TMB....)
HIV tests are almost always a two-part test. The first test is almost always the ELISA test. This test is relatively cheap to administer, and gives quick results. And it has two important characteristics: high sensitivity and low specificity. This essentially means that if the person being tested does have HIV, this test will almost always come back positive (high sensitivity), but if the test comes back positive, it may be for reasons other than that the person being tested has HIV (low specificity).
In other words, a negative ELISA test means that the patient almost certainly is not HIV+. Therefore, if the ELISA test comes up negative, the person is told that they do not have HIV, and no further testing is necessary (apart from perhaps another test later in time, to allow for incubation periods). However, if the ELISA test comes back positive, then this means that the person
might be HIV+.
It's at this point (positive ELISA test) that two things happen: firstly, the patient is usually told that they
might be HIV+, but that there is a significant chance that the ELISA test is giving a false positive; and secondly, the second test - the Western Blot test - is performed. This test is the perfect complement to ELISA, as it has low sensitivity and high specificity (the opposite to ELISA).
What this means in practice is that if the person tests positive with ELISA and negative with Western Blot, they almost certainly
are not HIV+. But if the person tests positive with both ELISA and Western Blot, then they almost certainly
are HIV+. (And of course if they test negative with ELISA, they are almost certainly not HIV+, and no Western Blot test is performed).
So what does this all mean in relation to Knox? It means that she had the ELISA test performed on her blood first. Personally, I suspect that she
did come back positive with ELISA (it's very possible that the fact that she carried herpes simplex (via a cold sore) might have produced a false positive). But Knox was in a low-risk group for HIV, and it's the low-risk groups that have the highest proportion of false positives.
Therefore, what Knox should have been told - if indeed the ELISA test came back positive, was that she'd tested positive with the first test but that there was a good possibility that it was a false positive, and that only the second test would truly tell whether she was indeed HIV+. In other words, she most definitely should not have been frightened or told in any way that she was HIV+.
If Knox's account is to be believed (and, given her known actions (diary entries etc), I'd say there's little reason to disbelieve her here), then it appears that the authorities might have acted way outside accepted protocols - and WHO guidelines - in how they dealt with a positive ELISA test in a low-risk-group individual. It appears that they put the fear of God into Knox by implying that she really was most likely HIV+, and it also appears that they may have used the situation as a device for getting Knox to divulge her sexual history. Personally (again), I wonder whether they hoped Knox was going to list Guede in her sexual partners.....?
