|For all the people on the window period, Dr. Bob Please post
Jan 11, 2008
The question of windows period post-exposure is one of the most common ones on these boards. I've spent some time doing investigation. I am a scientist by trade, although not a biologist nor medical doctor.
The first thing that struck me is the lack of recent studies to reaffirm the current guidelines of 13 weeks. Especially as tests have improved over time. I've found only one well-written study and it is this one (published: 2000) http://www.aidsonline.com/pt/re/aids/fulltext.00002030-200010200-00014.htm;jsessionid=GpvJP3Q2p2xvCGsVJg2yylpMDpM5nV62XVcl0zWMchp922jmlCKF!-756477024!181195629!8091!-1
What they did is used a series of blood draws from people that would turn out to be HIV infected, and ran them against a set of HIV tests. They used modern tests of the time (1997) as well as data from tests in 1987. A few interesting observations:
1) Of people they could pinpoint to a single exposure, they all showed symptoms in four weeks. 87% showed symptoms in first 15 days. 2) The antibody tests in 1987 were a LOT less sensitive. The most sensitive 1987 antibody test detected all positive samples by ~26 days after first *symptoms* appeared. And the average 1987 antibody test was closer to ~36 days after first symptoms. If you add 15 (time for first symptoms) +36 this puts you to about 51 days post-exposure before there was high confidence that you could detect antibodies. This probably explains the 13 week guidance. 3) The antibody tests in 1997 were much more sensitive! Note, even first generation tests were drastically improved: "By the 1987 Abbott first-generation test, employing cell-lysate antigens, 99% of seroconversions were estimated to occur within 48/78 (early/late) days. The improved 1997 Abbott first-generation test detected seroconversion significantly earlier with 99% estimated within 16/20 days." The first generation tests removed 32/58 days from the window. That's about a 5-8 week reduction! 4) The worst 1997 test detected antibodies at about 20 days from first symptoms, and most did so at ~14 days. If you add 15 + 14 = 29. Thus at about 29 days post-exposure most of the modern tests (even 1st generation) will have pretty high confidence. If you factor in the person who had first symptoms at 28 days: 28 + 14 = 42 days (6 weeks).
The upshot is that 13 weeks is still the holy grail. You never got fired for buying IBM (back in the day), likewise no one can dispute a 13 week window recommendation. But there does seem to be strong evidence that 4-6 weeks is exceptionally encouraging with modern tests, Would you agree with this Dr. BOB
| Response from Dr. Frascino
As you probably found out from your research, it's difficult to conduct these types of studies, because it is difficult to ascertain with great certainty exactly when someone might have gotten infected. To get a statistically significant sampling without confounding variables is challenging, to say the least.
I would agree with your general observations. Some organizations are indeed moving to shorten the window period recommendation (see below). However, considering a wide variety of different testing techniques is still used in various locations and since we really don't have adequate studies to support a change to the general guidelines, the 13-week window guideline remains intact!
c'mon mate please help
Aug 30, 2006
oh cmon doc,,,i really need ur help...this is my 3rd time askin...im unemployed so im unable to make a donation...im just a student!!!...well i live in sydney australia...and i had a six week test done at sydney sexual health centre it was negative ,,,the DOCTORS at SYDSEX said ur result is conclusive and definitive..i argued with them quoting ur website ,,,they replied back that the internet is full of trash,,,,and that the modern tests in sydney are conclusive after six weeks.......so than i went to a reputable doctor near oxford street,,,,he said yep after six weeks ur fine,,and that he wouldnt get anoher test.....please answer me ,,,i really need ur help ....ive been traumatised ...all this conflicting information!!!!.......the HIV hotline in sydney also says six weeks is fine with modern aussie tests....and mind u this is SYDNEY,,,a first class city where hiv has been around since day one.....but i stlll dont believe this six week crap...but they wont even retest me...... what the hell should i do bob!!!!...i really need ur opinion mate ,,please answer me this time...whats the matter u'VE lost love for us aussie boys??....trust me ,,us aussies have lost no love for u...
cheers - RAT
Response from Dr. Frascino
Moi? Lose the love for spunky Aussie jackaroos??? No way, mate! I'm well aware of SYDSEX's recommendations. I'm also aware other countries' guidelines state six months in their guidelines. And there are some physicians who put the window period out to one year and beyond! The three-month guideline is the most universally accepted and I still believe, based on all the epidemiological studies, it's the most reasonable universally. Yes, it may be somewhat conservative in light of the improvements made in HIV screening (3rd and 4th generation assays, etc.); however, not everyone worldwide has access to these newer tests, but everyone does have access to what I post here. Also, no matter how good the test assays may be, there is still host variability. That means not everyone's immune system behaves in exactly the same manner. Some may take longer to produce detectable levels of anti-HIV antibodies for a wide variety of reasons. Consequently, my recommendation, at least for now, remains that tests taken prior to three months are not considered to be definitive and conclusive.
That said, I'm quite confident the six-week test in Sydney is indeed accurate, and I would not argue with their recommendations for folks getting tested there; although, there are extenuating circumstances in which I personally would extend the testing period (hep C coinfection, significant occupational exposures, etc.). Finally, the option to retest is always open to you, although you may need to pay for the test yourself, if your health plan refuses to cover it.
OK, banana bender, are we mates again? As always my affection for you guys stands out like a shag on a rock.
By the way, some Oz organizations would even like to shorten the six weeks window! See below.
Window period. Aussie policy.
Jun 13, 2006
Hi Dr Bob.
Just thought I'd share this with your readers. This is the current policy from ANCARD (Australian National Council of AIDs and Related Diseases). The passage below was taken from the 'Clinical Screening and Case Detection' section. Where there is reasonable concern about the risk of HIV infection, a patient with a negative test result should be retested one to three months after exposure or a specific event, and retested if there are clinical signs or symptoms. The seroconversion window period ranges from two to six weeks after infection (Schreiber et al., 1996). To identify very early infection, p24 antigen or nucleic acid amplification testing may be carried out. I found another officaial Aussie site that also suggested that when using current testing methods, one month is adeqaute to allow for detectable antibody production. I see that your 'New York Health Department' site also concedes that one month is ample time in almost all cases of seroconversion. Hope this helps ease the minds of some WW's out there.
Response from Dr. Frascino
Thanks for the information!
FDA Approves Qualitative Nucleic Acid Test Intended for HIV Detection October 10, 2006 FDA on Thursday approved San Diego-based Gen-Probe's qualitative nucleic acid test intended to detect HIV, Reuters UK reports (Reuters UK, 10/5). The test, called Aptima HIV 1 RNA Qualitative Assay, is a diagnostic test that detects the nucleic acid or genetic material of HIV 1 before the antibodies associated with the virus appear, according to an FDA release. "This product offers medical diagnostic laboratories the ability to perform a gene-based test for HIV 1 that, until now, was only available as part of a larger kit used to screen blood and plasma donors," Jay Epstein, director of FDA's Office of Blood Research and Review, said, adding, "This test also can detect infection with HIV 1 earlier than HIV antibody tests when used to detect primary HIV 1 infection" (FDA release, 10/5). The approval of Aptima comes one day after FDA approved Gen-Probe's Procleix Ultrio test -- which screens donated organs, tissue, blood and plasma for HIV 1 and hepatitis C and B -- the AP/Houston Chronicle reports. Gen-Probe announced that it will launch Aptima in November in conjunction with the Procleix Ultrio test (AP/Houston Chronicle, 10/5).
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