Testing window Periods

[15 dollars well spent]

Dear Dr HHH,
It is nice to see expert opinions based on research rather than the usual 'copy and pasted' facts on HIV Testing on several government sponsored web sites.
I have been tested negative for HIV antibodies just a bit over 12 weeks following possible exposure (through heterosexual intercourse). I come from the UK and the person I was with had several unprotected sexual encounters with partners overseas (mostly Europe). Naturally I was a bit concerned when I later discovered this.
You will notice on a lot of sites the following copied and pasted statement: "Most people develop detectable HIV antibodies within 6 to 12 weeks of infection. In very rare cases, it can take up to 6 months. It is exceedingly rare for someone to take longer than 6 months to develop antibodies."
Do these rare cases really exist and are they documented or is this just wish-wash based on lawsuit paranaoia? And if they do really exist how come you are so confident that a test 6 weeks after exposure should suffice. Has there really been a case of someone testing positive for HIV only after (say 5 months) but was tested negative (say 6 weeks after exposure)? It is quite interesting to notice that on almost all these sites including this one there are disclaimers. But what are the real case facts? I sincerely apologies in advance if you had answered a similar question before but please be rest assured that I had read almost every post on this site and did not find anything on this subject.

[H. Hunter Handsfield, M.D.]

You correctly cite the expert party line.  However, to my knowledge, the supposed rare cases of delayed seroconversion beyond 3 months were never clearly proved.  You have to understand that the only way to know if such cases exist depend entirely on infected persons' histories of when and where they were exposed.  The vast majority of infected people have multiple potential exosures, but may firmly believe that a particular source was the only possible time and place of possible infection--but may be wrong.  There just isn't that much precision on time to seroconversion. To the extent there might be rare cases of such prolonged delays, to my knowlege this has not been documented with the HIV tests developed within the past several years.  At a meeting of ~300 HIV/AIDS specialists that I attended last November, the moderator asked for a show of hands of providers who had seen even a single patient, tested within the past 5 years, who had a seroconversion delay beyond 3 months.  Not one hand was raised.

There just isn't all that much precision available.  To know the exact risk of delayed seroconversion, a study would have to be done of several hundred (maybe thousands) of people exposed only once at a particular time; and they would have to be tested regularly (e.g., once a week) for 6 months.  That kind of research never will be done.  (In theory, of course you could do a study in which people were intentionally exposed, then followed regularly to measure time to seroconversion.  But of course that study woudl be ethically impossible.)

Bottom line:  We'll never know precise statistics on the potential for very rare late seroconversion (beyond 3 months); and any data we ever will have would have to be based on fallible human memory, not precise data.  Twenty years from now we will not really know more about this than we do now.  What we can say with confidence is that seroconversion later than 6-8 weeks is uncommon to rare with modern tests, and is so rare beyond 3 months that it can be disregarded.

Sorry for the vague answers--but the science is vague.  Best wishes--

HHH, MD

[15 dollars well spent]

Dear Doctor Handsfield,

Last question - a spanner in the works for you, I am interested purely for educational reasons (I should have studied medicine and especially immunology).

Scenario: A person has been contaminated with the HIV Virus on the 1st of June for one reason or another. A few days later he gets a viral infection (say the common flu, that many people around him have been experiencing of late) and takes say 4 to 5 weeks to shake off. Now my question, if the immune system is busy fighting off the flu virus, I would assume that it is weakened and therefore unable to produce antibodies to the HIV virus before the 6 weeks testing period.

Be straight with me Doctor, is this the dumbest question you have heard? Just interested to see if this is a factor that could delay seroconversion.

All the best

[H. Hunter Handsfield, M.D.]

Please take any further discussion over to the HIV support forum.

Thanks--  HHH, MD

[15 dollars well spent]

With all due respect nerviouskid you didn't quite understand my question and although I appreciate your response (which is probably right) - I was hoping someone like Dr Handsfield could answer this question since he has studied immunology and has published numerous articles on the subject. The case I make is that HIV had nothing to do with another flu-like illness caused by a random virus, the immune system would attack the virus and slowly get weakened and interested to know where it can produce detectable antibodies by the first few weeks (assuming the person has been ill with another virus for a long period).

[H. Hunter Handsfield, M.D.]

15D:  There is no evidence that such an event would delay HIV seroconversion.  The immune system is perfectly capable of responding simultaneously to many such exposures.

NK:  Thanks for the thanks.  Glad it helped.

But I think that's enough for this thread.  Take care--

[nerviouskid]

Your response: "That's reassuring, but most people would want still greater reassurance."

You hit it perfectly with your explaination.  That was very informative in addition to the questions answered to the original poster regarding Window period and testing timeframes.  This was a good thread for knowledge.  Thanks again.

15 Dollars - I think even if you were down with a flu or some kind of other viral infection, I assume logically that HIV has absolutely nothing to do with with it since it is such an isolated disease.  One would still develop antibodies for HIV if infected and testing at 6-8 weeks would be warrented.  

[15 dollars well spent]

Dear Dr Handsfield,

Thank you very much for your prompt reply. For scientific reasons, I can think of a few people we can do tests on so we can get a definitive answer, so its not entirely unethical to do so :). Obviously I'm thinking of political figures, lets face it, no innocent lives would be at risk and its for the better of mankind.

I know you can't joke with this so I thank you so much for your interesting feedback and bid you an excellent day.

Regards,

Nick

[H. Hunter Handsfield, M.D.]

Like peekawho said.  Read through the archives and/or search for "time to positive HIV test".

I know it is confusing, so the point bears repeating; and it is pertinent to 15dollars' question.  My risk assessments are based on the overall situation, not test performance alone.  The test works the same regardless of the level of risk.  

Consider someone whose risk of catching HIV was, say, 1 in 100,000, which probably is typical for most exposure questions on this forum. A test with 99% accuracy (e.g., at 6-8 weeks) converts that person's chance of having HIV from 1 in 100,000 to 1 in 10 million, i.e. zero for practical purposes.  Even the world's most anxious person should, in theory, be totally reassured by such a result.

However, if someone's risk is higher to start with, say 1 chance in 100, as for receptive anal sex with a known infected person, then the same negative result at 6-8 weeks still leave a 1 in 10,000 chance the person caught HIV.  That's reassuring, but most people would want still greater reassurance.  So that person requires later testing, e.g. at 3 months.

Same test at 6-8 weeks but different interpretation, based on the overall risk assessment.

Got it?

[peekawho]

He's explained this numerous times.  

[nerviouskid]

Hello Dr. H, I just want to say that, that was a good response to 15 dollars' question on window period and testing.  However, this is not intended as a thread jump, but more in sync with the question on seroconversion between a high and low risk individuals.  Correct me if I am wrong, but is it not true that sometimes you do ask the patients who post here to test out to 12 to 13 weeks if they belong to very high risk exposure (such as unprotected anal)?  I am not sure but would need some clarification in terms of seroconversion time between single heterosexual exposure vs. homosexual incidents.  Your feedback on this testing and window period is much appreciated.  

I gather that typically 8 weeks should be conclusive for all parties, whether high risk or low risk, but I am not sure why the suggestion of 12 to 13 weeks is mandatory in some cases.  Is it to suggest ease the mind more than anything else?

Thanks again.