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Medical Forum / Diseases and Disorders / AIDS / November 2006Pregnancy and False Positive HIV Tests
Here is why pregnant women test false positive on HIV tests. And why tests that rely on blood from pregnant women are singularly unreliable. Like all the surveys that 'show' that 30%, 50%, etc. of women in Botswana, Swaziland, etc. are 'HIV positive'. Apparently the placenta did it. " The nature and/or potential function of these particles/proteins has not yet been fully defined." " Remember that 'HIV tests' do not really test for HIV, but for proteins that are presumed to be unique to HIV. From the NIH: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?itool=abstractplus&db=pubmed&cmd=R etrieve&dopt=abstrac tplus&list_uids=7473433 "Expression of intact endogenous retroviruses by normal placental villous trophoblast and immuno-crossreactivity of villous trophoblast with anti-retroviral antisera have been documented. The nature and/or potential function of these particles/proteins has not yet been fully defined." Expression of endogenous HIV-1 crossreactive antigens within normal human extravillous trophoblast cells. Alex a ?crit : > Here is why pregnant women test false positive on HIV tests. > [quoted text clipped - 23 lines] > Expression of endogenous HIV-1 crossreactive antigens within > normal human extravillous trophoblast cells. Alex, it is of use to nothing, they have their agenda. You can demonstrate them by a+b that they are delirious, they have the power and take advantage of it. Thank you in any cases for the link. > Here is why pregnant women test false positive on HIV tests. > [quoted text clipped - 4 lines] > > Apparently the placenta did it. Alex - I told you about this 6 years ago!!! http://groups.google.com/group/misc.health.aids/msg/135f320fc95ac5a6 Cheers Bennett > > Here is why pregnant women test false positive on HIV tests. > > [quoted text clipped - 12 lines] > > Bennett And David Canzi specifically refuted Alex in this thread. http://groups.google.com/group/misc.health.aids/browse_frm/thread/792015eaa29c86c2/ Testing pregant women with a single ELISA does not give false positives at anywhere near 30-50%. You would think that even if Alex has memory problems that he would at least do a google search to check the last time somebody refuted his argument. Chris Noble ... > You would think that even if Alex has memory problems that he would at > least do a google search to check the last time somebody refuted his > argument. > > Chris Noble Don't you know that a lie, repeated often enough, becomes the truth? Maybe that is not the way it works in science and other versions of reality, but that is the way it works in AIDS denial and many forms of politics. > ... > > You would think that even if Alex has memory problems that he would at [quoted text clipped - 7 lines] > reality, but that is the way it works in AIDS denial and many forms of > politics. Or maybe Google's experience in China has allowed them to develop a variety of Denialist options that allows evolution "rethinkers", HIV "rethinkers", germ theory of disease "rethinkers" to surf the internet without being exposed to any information that might conflict with their worldview. Chris Noble > ... > > You would think that even if Alex has memory problems that he would at [quoted text clipped - 7 lines] > reality, but that is the way it works in AIDS denial and many forms of > politics. Or maybe Google's experience in China has allowed them to develop a variety of Denialist options that allows evolution "rethinkers", HIV "rethinkers", germ theory of disease "rethinkers" to surf the internet without being exposed to any information that might conflict with their worldview. Chris Noble > And David Canzi specifically refuted Alex in this thread. > [quoted text clipped - 8 lines] > > Chris Noble Actually, the explanation is very simple. You are confusing positives and false positives. Among pregnant women in the west, Positive ELISA tests are extremely rare. However, if you look at how many test positive, and then STAY positive after confirmation tests are carried out, False Positives are THE NORM. Then, you must have a clear explanation of why these 25%, 33% infection rates disappear as soon as testing involves non-pregnant girls in Africa. Or to be specific, why infection rates go from 32.5% to 6% in Swaziland. If there are any real infections at all. Also, don't count out the effect of environmental pollution, but that is for another thread. Alex UNICEF DHS IN SWAZILAND MBABANE, 27 August (PLUSNEWS) - A dramatically lower number of Swazi teenage girls are being infected by HIV than was previously estimated, suggesting a turning point in the battle against HIV/AIDS in a country with the world's highest HIV infection rates. The findings in the report, 'A Baseline Study on HIV Risk Factors', commissioned by the UN Childrens' Fund (UNICEF) are derived from interviews and blood tests of over 1,000 Swazis in two rural areas and revealed that only six percent of girls aged from 15 to 19 were found to be HIV-positive, with most of the HIV infections occurring among older girls. "This is the first time we have had data from a scientifically accurate survey of randomly selected households. It confirms some trends we had suspected, but which were belied by previous HIV estimates," said Dr Alan Brody, country representative for UNICEF. "This is different from anything that has been seen before. The conventional wisdom is that many more girls were infected," he told PlusNews. The study was prompted by the results of the government's 2002 sero-surveillance study, which estimated that 32.5 percent of teenage girls between the ages of 15 and 19 were HIV-positive. http://www.plusnews.org/AIDSReport.ASP?ReportID=3819&SelectRegion=Southern_Afric a&SelectCountry=SWAZ ILAND [Wow, now we're getting to the meat of things. Of 26 positive Rapid ELISAs, only 26 REMAINED positive after Western Blot testing. So much for false positives being 'extremely rare'. You see the key is, that you compare the number of false positives to the total number of positives, not the total number of people who were tested, most of whom in the West test negative. This would put the number of False Positives among positive testing pregnant women at a whopping 62.3% and the percentage of True Positives 37.7%. It doesn't need to be repeated that confirmation tests in surveys in Swaziland are NEVER carried out - Alex] http://cat.inist.fr/?aModele=afficheN&cpsidt=16551024 RESULTS: A total of 69 patients had a positive rapid HIV-ELISA out of 9,781 deliveries. Of those, 26 were confirmed as HIV infected by Western blot (overall HIV prevalence: 0.27%, ELISA-positive predictive value: 37.7%). http://womenshealth.about.com/cs/aidshiv/a/aidshivwomen_2.htm A reactive test may give a false positive reading to anyone with kidney or renal failure, to a woman that has had multiple pregnancies, anyone receiving the influenza vaccine, or to anyone that has received gamma globulin. http://www.dmt123.com/qa/pregnancy_false_positive_hiv_ask_851-dmt123.html Can pregnancy cause a false-positive HIV test result? Question I am pregnant, and I just had an HIV test done. To my horror, it came back positive. As I was commiserating with my girlfriend, she said that she heard that being pregnant could cause a false positive result. Is this true? Answer Yes, pregnancy can occasionally cause a false positive HIV antibody test. Thank you for your question. [Comment - notice that this says nothing about ELISA only tests, which is what we are talking about in surveys, including in Swaziland; it most likely refers to results from multiple tests, including Western Blot, or some calculation that takes into account all tests in a huge survey, most of which are negative in the West - Alex] http://www.sogc.org/health/pregnancy-hiv_e.asp Although it is extremely rare (about 1 out of every 20,000 tests,) a test may give a false-positive result.. A false-positive test says you are infected when you are not. If there are any doubts, you can be retested. [So much for false positives being 'extremely rare', and this is in a non-tropical, well to do environment - Alex] http://findarticles.com/p/articles/mi_m0838/is_120/ai_107894045 One out of 14 previously pregnant women given the OraQuick Rapid HIV-1 Antibody Test, which the CDC is promoting, showed false positive results. (6, 7) http://www.thebody.com/Forums/AIDS/Women/Archive/WomenInfected/Q141298.html HIV False + & Pregnancy Sep 2, 2002 I was recently tested for HIV in January 2002 with the result being negative. I hadn't slept with anyone in over 9 months. I then became intimate with someone else 6 months later and almost immediately became pregnant which led to a routine test for the HIV virus. After just two months of being with this individual I received a HIV positive test. The Westeren Blot has not been administered yet. I am to have it done in a few more months. However, my question is, would a test come up positive in just 2 months and what causes a pregnant womans test to come back as a false positive. The antigens or antibodies that can possible become active in pregnant able to reproduce at a faster rate than in someone recently infected. Please, please respond as I am depressed beyond belief. Response from Dr. Aberg Prgenancy may cause a false positive screening test called an Elisa. The western blot should have been done on the same specimen and the results back relatively soon unless there was not enough blood sample to be tested. Has your partner been tested? If he is the only one you have had sex with since your last negative test and he is negative, then that may help ease your mind. If your doctor and you are concerned that you just acquired HIV, then you should have a HIV viral load measured and antibody testing in follow up. You can have false positive HIV viral loads but the amount of virus is usually much lower than one would expect in primary infection. Best to do repeat Elisa and if positive, western blot testing. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstra ctPlus&list_uids=962 9106&itool=pubmed_AbstractPlus New, third-generation HIV tests have reduced false-positive rates and thus diminished the harm of screening. > > And David Canzi specifically refuted Alex in this thread. > > [quoted text clipped - 14 lines] > rare. However, if you look at how many test positive, and then STAY > positive after confirmation tests are carried out, False Positives are THE NORM. Now you are confusing specificity with positive predictive value. > Then, you must have a clear explanation of why these 25%, 33% infection > rates disappear as soon as testing involves non-pregnant girls in Africa. There are many reasons why seroprevalence statistics from pregant women may overestimate seroprevalence in non-pregnant girls. What I find interesting is that seroprevalence based on antenatal scrrening has increased over time. The first national antenatal survey in South Africa found a prevalence of only 0.8%. This has increased dramatically over time. Why? > Or to be specific, why infection rates go from 32.5% to 6% in Swaziland. > If there are any real infections at all. > > Also, don't count out the effect of environmental pollution, but that is > for another thread. Environmental pollution causes false positives on HIV tests? Chris Noble > > Actually, the explanation is very simple. You are confusing positives > > and false positives. [quoted text clipped - 3 lines] > > Now you are confusing specificity with positive predictive value. No I'm not. Please check again, I said 'if you look at how many test positive'. Most of those who test positive on ELISA are false positive (they don't stay positive after confirmation testing with Western blot. In Africa, you just have a lot more people who test positive. I never understood why it is presumed why there are only huge numbers of false positives ELISAs when very few people out of the total survey test positive on ELISA, than when many people in a survey test positive on ELISA. What I would like to see, is a survey that uses both ELISA for screening purposes, and Western Blot to confirm positive ELISAs. What is happening right now, is that DHS surveys only use Western Blot on ELISAs that seem neither positive nor negative. So if you know of a DHS type survey in Africa, that uses Western Blot as a confirmation test, that would be great. > > Then, you must have a clear explanation of why these 25%, 33% infection > > rates disappear as soon as testing involves non-pregnant girls in Africa. > > There are many reasons why seroprevalence statistics from pregant women > may overestimate seroprevalence in non-pregnant girls. Not according to UNAIDS, who for years have used ELISA tests of pregnant women as a direct proxy for national infection rates. Which is why you ended up with the 33.4% of (adult) Swazis are HIV positive yarns. (Source: Adult HIV prevalence (%), 2003 33.4) http://www.hivinsite.org/global?page=cr09-wz-00 So, the HIV Insite, which still shills the UNAIDS (political) line, still claims that 33.4% of adults in Swaziland (15-49 years of age) are HIV positive. This of course coincides approximately with the belief that 32.5% of pregant women in Swaziland were HIV positive. (Source: http://www.plusnews.org/AIDSReport.ASP?ReportID=3819& SelectRegion=Southern_Africa&SelectCountry=SWAZILAND ) What you see here, and this is the criminal part, is the direct translation of results from pregant women, to the entire (adult) population. And that was always unscientific, and anti-scientific, even if you believe that the tests are accurate, that HIV causes AIDS, etc. You can believe all of that, but still, just as someone with a vague background in surveys and statistics, know that you cannot simply extrapolate the results from pregnant women at antenatal clinics, to everyone in the population. And that is where I think UNAIDS is criminally negligent. > What I find interesting is that seroprevalence based on antenatal > scrrening has increased over time. The first national antenatal survey > in South Africa found a prevalence of only 0.8%. This has increased > dramatically over time. Why? What year was that? If it was during apartheid, did they only screen white pregnant women? Please include the source. > > Or to be specific, why infection rates go from 32.5% to 6% in Swaziland. > > If there are any real infections at all. [quoted text clipped - 3 lines] > > Environmental pollution causes false positives on HIV tests? Depends on what makes the already extremely sensitive ELISA HIV test make positive. Whether that is exposure to DDT, copper, mercury, etc. I don't know. What I do know, is that environmental exposure to banned pesticides, pollution, industrial spills etc. is much greater in Africa than in Oxford, just to mention one place. Alex > > > Actually, the explanation is very simple. You are confusing positives > > > and false positives. [quoted text clipped - 7 lines] > Most of those who test positive on ELISA are false positive (they don't stay > positive after confirmation testing with Western blot. This is true of any test applied to a low prevalence population. In a low prevalence population even highly specific tests can have a low positive predictive value. All positives resulting from testing a group of men with a pregnancy test will be false positives. > In Africa, you just have a lot more people who test positive. I never understood > why it is presumed why there are only huge numbers of false positives ELISAs > when very few people out of the total survey test positive on ELISA, than when > many people in a survey test positive on ELISA. If a test is 99.9% specific and you test 1000 people then you would expect 1 false positive. If you get 300 testing positive it is very unlikely that a significant proportion would be false positives. > What I would like to see, is a survey that uses both ELISA for screening > purposes, and Western Blot to confirm positive ELISAs. [quoted text clipped - 4 lines] > So if you know of a DHS type survey in Africa, that uses Western Blot > as a confirmation test, that would be great. Some surveys have used multiple ELISAs of different contructions. These protocols are comparable to ELISA + WB. > > > Then, you must have a clear explanation of why these 25%, 33% infection > > > rates disappear as soon as testing involves non-pregnant girls in Africa. [quoted text clipped - 5 lines] > ELISA tests of pregnant women as a direct proxy for > national infection rates. Nobody simply equates the HIV prevalence from antenatal clinics to the general population. Statistical models are used. The final figure is an *estimate* with a confidence interval. The true figure may be substantially lower but still way too big to deny. > Which is why you ended up with the 33.4% of (adult) Swazis are HIV positive yarns. > [quoted text clipped - 35 lines] > > Please include the source. http://www.doh.gov.za/docs/reports/2002/hiv-syphilis.pdf The first survey was in 1990. The data is from women attending antenatal clinics and if anything undersample white women. > > > Or to be specific, why infection rates go from 32.5% to 6% in Swaziland. > > > If there are any real infections at all. [quoted text clipped - 7 lines] > HIV test make positive. Whether that is exposure to DDT, > copper, mercury, etc. I don't know. Well, the last three words are true. > What I do know, is that environmental exposure to banned > pesticides, pollution, industrial spills etc. is much greater in > Africa than in Oxford, just to mention one place. These pollutants are definitely major health risks but it is hard to see how they could possibly have an effect on HIV tests. Chris Noble > > > > Actually, the explanation is very simple. You are confusing positives > > > > and false positives. [quoted text clipped - 11 lines] > low prevalence population even highly specific tests can have a low > positive predictive value. That is just a restatement, not an explanation. > All positives resulting from testing a group > of men with a pregnancy test will be false positives. What exactly is the low frequency of pregnant men in that survey population? Could it be zero? So perhaps you are saying that the ELISA HIV test is irrelevant to the testing of HIV, like a pregnancy test is irrelevant to men? Seriously though, if a test is truly 99% specific and sensitive, then it shouldn't matter what the prevalence in the test population is. The ppv should be exactly the same. Unless there are factors that influence false positive results, and that differ from population to population. > > In Africa, you just have a lot more people who test positive. I never understood > > why it is presumed why there are only huge numbers of false positives ELISAs [quoted text clipped - 3 lines] > If a test is 99.9% specific and you test 1000 people then you would > expect 1 false positive. I'm not talking about specificity (false positives out of all uninfected people) or sensitivity, I am talking about positive predictive value, which looks at who tests false positive out of all positive tests. > If you get 300 testing positive it is very unlikely that a significant > proportion would be false positives. And if out 10,000 people, and 69 test positive? Because that is the example we're dealing with. And of course, the numer of false positives wasn't 1, or 10, but 40. Also, you are presuming that specificity is a constant. However, shouldn't specificity be directly related to the very factor that makes false positives false positives? If you test 10,000 ordinary citizens, shouldn't the specificity of a test be different than when you test 10,000 pregnant women? If you say that pregnancy is a factor in causing false positive results, then the number of false positives should change with whatever subpopulation you test? And if that is true for pregnant women, what happens when you shift your testing population to an entirely different continent? > > What I would like to see, is a survey that uses both ELISA for screening > > purposes, and Western Blot to confirm positive ELISAs. [quoted text clipped - 7 lines] > Some surveys have used multiple ELISAs of different contructions. These > protocols are comparable to ELISA + WB. They're not the same. And the FDA doesn't approve anything of the sort for diagnosis if HIV/AIDS in the US. The CDC only used Western Blot in cases where ELISA results are 'anomalous' (their word). What they do not do, is use Western Blot as a confirmation test for positive ELISAs, which is required for diagnosis of individual patients, in the US. > > > There are many reasons why seroprevalence statistics from pregant women > > > may overestimate seroprevalence in non-pregnant girls. [quoted text clipped - 7 lines] > *estimate* with a confidence interval. The true figure may be > substantially lower but still way too big to deny. Yes they did and do. Notice again the presumed 32.5% of HIV prevalence among pregnant Swazi women at antenatal clinics, and the 33.4% national prevalence among adults (15-49 years). > > Which is why you ended up with the 33.4% of (adult) Swazis are HIV positive yarns. > > [quoted text clipped - 38 lines] > http://www.doh.gov.za/docs/reports/2002/hiv-syphilis.pdf > The first survey was in 1990. A lot of changes happened between 1990 and 2002. There was a lot of urbanisation (meaning a lot of people from the countryside were able to move to the cities). If you look at the chart (figure 1) much closer, you will see that the significant changes were between 1992 and 1998. From 1998 to 2002, the numbers pretty much stayed the same. So what happened between 1992 and 1998? Well, the so-called independent homelands were dismanteled and became officially part of South Africa. We had this discussion before, when William Makgoba used very similar data to claim that South Africa was being decimated by an AIDS epidemic. That was back in 2000, when the population was under 44.8 million (2001), while it is 47.4 million today (mid-year estimate 2006). See much of the arguments recounted in the article: NOT-SO-YOUNG, NOT-SO-GIFTED AND DEAD WRONG! http://www.virusmyth.net/aids/news/noseweek.htm > > Depends on what makes the already extremely sensitive ELISA > > HIV test make positive. Whether that is exposure to DDT, > > copper, mercury, etc. I don't know. > > Well, the last three words are true. And neither do you know. > > What I do know, is that environmental exposure to banned > > pesticides, pollution, industrial spills etc. is much greater in > > Africa than in Oxford, just to mention one place. > > These pollutants are definitely major health risks but it is hard to > see how they could possibly have an effect on HIV tests. So what does have an effect on HIV tests, and how? What exactly is it that makes a false positive ELISA from a pregnant woman false positive? What protein? What antibody? Alex Just to recap: Specificity = (True Negatives)/(True Negatives + False Positives) Sensitivity = (True Positives)/(True Positives + False Negatives) Positive Predictive Value = (True Positives)/(True Positives + False Positives) Negative Predictive Value = (True Negatives)/(True Negatives + False Negatives) > > > > > Actually, the explanation is very simple. You are confusing positives > > > > > and false positives. [quoted text clipped - 19 lines] > What exactly is the low frequency of pregnant men in that > survey population? Could it be zero? That is exactly my point. > So perhaps you are saying that the ELISA HIV test is irrelevant > to the testing of HIV, like a pregnancy test is irrelevant to men? No. We can safely say that men are not pregant without giving them a pregnancy test. The same is not true for women even in low prevalence populations. > Seriously though, if a test is truly 99% specific and sensitive, then > it shouldn't matter what the prevalence in the test population is. > The ppv should be exactly the same. No. You obviously do not understand what the term means. http://en.wikipedia.org/wiki/Positive_predictive_value PPV is a function of prevalence! > Unless there are factors that influence false positive results, > and that differ from population to population. [quoted text clipped - 29 lines] > And if that is true for pregnant women, what happens when you shift > your testing population to an entirely different continent? As we saw from the famous "Voevodin letter" the false positive rate froma a single ELISA is only marginally higher in pregant women. It is within the realms of possibility that the false positive rate in pregnant women is higher in Africa but the assertion needs evidence rather than ad hoc reasoning. Personally, the reason why I find this scenario extremely unlikely is that the seroprevalence of women attending antenatal clinics in South Africa in 1990 was less than 1%. You need to provide a rational explanation for why the false positive rate in preganant wome should increase dramatically over time. Ad hoc explanations that ultimately stem from your initial assertion that they are false positives do not count. > > > What I would like to see, is a survey that uses both ELISA for screening > > > purposes, and Western Blot to confirm positive ELISAs. [quoted text clipped - 15 lines] > Blot as a confirmation test for positive ELISAs, which is required > for diagnosis of individual patients, in the US. Can you provide some evidence for this statement. > > > > There are many reasons why seroprevalence statistics from pregant women > > > > may overestimate seroprevalence in non-pregnant girls. [quoted text clipped - 11 lines] > among pregnant Swazi women at antenatal clinics, and the 33.4% > national prevalence among adults (15-49 years). Can you provide the references to the actual study and the methods used. You have simply pulled out two figures from different sources and implied a connection. > > > Which is why you ended up with the 33.4% of (adult) Swazis are HIV positive yarns. > > > [quoted text clipped - 76 lines] > > So what does have an effect on HIV tests, and how? It depends on the test. Antibodies to other retroviruses. > What exactly is it that makes a false positive ELISA from a pregnant > woman false positive? What protein? What antibody? Probably the expression of a HERV. I don't know which proteins generate antibodies that cross react with HIV antigens. Chris Noble "Chris Noble" <ChrisJNoble@hotmail.com> wrote in message > These pollutants are definitely major health risks but it is hard to > see how they could possibly have an effect on HIV tests. That's because you use your brain. Others, like Alex, don't use theirs so they come up with all sorts of drivel. -- Moira de Swardt posting from Johannesburg, South Africa Remove the dot in my address to find me at home. > "Chris Noble" <ChrisJNoble@hotmail.com> wrote in message > [quoted text clipped - 4 lines] > That's because you use your brain. Others, like Alex, don't use > theirs so they come up with all sorts of drivel. Oh pray tell, Moira, how is Chris 'using his brain' when he states it is 'hard to see how they could possibly have an effect on HIV tests'? Are the facts know what, and especially HOW, unknown factors are responsible for false positives when using the HIV ELISA test? Time to use YOUR brain, Moira. Alex "Alex" <avdeelen.REMOFETHIS1@wanadoo.nl> wrote in message > Oh pray tell, Moira, how is Chris 'using his brain' when he > states it is 'hard to see how they could possibly have an effect > on HIV tests'? Because it is hard to see how they could possibly have an effect on HIV tests unless one is daft or stupid. > Are the facts know what, and especially HOW, unknown > factors are responsible for false positives when using the > HIV ELISA test? While false positives to the ELISA certainly exist, there are very few false positives even to the ELISA. No-one in South Africa is *diagnosed* with an ELISA, a situation which has existed since almost the beginning although ELISA tests were used for statistical purposes. > Time to use YOUR brain, Moira. I've been using it since the beginning, but I'm not a denialist. -- Moira de Swardt posting from Johannesburg, South Africa Remove the dot in my address to find me at home. > > (CNob:Environmental pollution causes false positives on HIV tests?) > Depends on what makes the already extremely sensitive ELISA > HIV test make positive. Whether that is exposure to DDT, [quoted text clipped - 3 lines] > pesticides, pollution, industrial spills etc. is much greater in > Africa than in Oxford, just to mention one place. Your hypothesis seems to be that something which you claim is commoner in Africa (environmental pollution) is the cause of something else you claim is commoner in Africa (false positive HIV tests). Usually when someone proposes a hypothesis there is an underlying plausible explanation. What is yours? Do you have any reason to believe that pollution might lead to false positive serological tests? Please share the evidence with us, and we can decide for ourselves. Why do you think there is more pollution in Africa? It is a vast continent, largely unsullied by the industrialisation we have in the West. Sure, some localised spots are very contaminated because of local industries and toxic waste dumping. But in the 3rd world one is more likely to find widespread industrial pollution in countries like Brazil with their unusual mining methods. And if you really want to see bad pollution, go to countries like Estonia. Do they have high rates of false positive HIV tests? And why single out pollution as a cause anyway? Why not pick on something else common in Africa, like sunshine? > And why single out pollution as a cause anyway? Why not pick on > something else common in Africa, like sunshine? Heck, that might explain why the HIV prevalence rate in the UK is substantially lower than that in the US :o) Cheers Bennett Perhaps he subscribes to the theory: "Don't blame it on the sunshine, Don't blame it on the moonlight, Don't blame it on the good times, Blame it on the boogie." > Actually, the explanation is very simple. You are confusing positives > and false positives. > Among pregnant women in the west, Positive ELISA tests are extremely > rare. However, if you look at how many test positive, and then STAY > positive after confirmation tests are carried out, False Positives are THE NORM. Err, but by definition if the confirmation tests are negative, then the test is negative. A false positive would be a positive ELISA AND confirmation test, when in fact there was no HIV present. > Then, you must have a clear explanation of why these 25%, 33% infection > rates disappear as soon as testing involves non-pregnant girls in Africa. > > Or to be specific, why infection rates go from 32.5% to 6% in Swaziland. > If there are any real infections at all. The article you quote from gives you that answer. It's simply that the 32.5% of girls who were tested in the early years GREW OLDER. "Nevertheless, the new baseline survey found a 40 percent HIV-prevalence rate among older girls, from 19 years upwards, which matched the sero-surveillance study results." You don't help your case much Alex when you either fail to read the articles properly or (worse) are misrepresenting them on purpose. The seropositive rates dropped because kids stopped having unprotected sex (which would only work, of course, if they were preventing transmission of a sexually transmitted infection!) http://www.plusnews.org/AIDSReport.ASP?ReportID=3819&SelectRegion=Southern_Afric a&SelectCountry=SWAZILAND > http://womenshealth.about.com/cs/aidshiv/a/aidshivwomen_2.htm > A reactive test may give a false positive reading to anyone with kidney > or renal failure, to a woman that has had multiple pregnancies, anyone > receiving the influenza vaccine, or to anyone that has received gamma > globulin. Sadly the bit about the flu vaccine is probably wrong, and based upon one batch of one years vaccine from one company reacting with polystyrene beads in one type of HIV ELISA (no false positives occured as the WB's were all negative). One of the perils of believing everything you read from the web. The rest we already know - hell we had a case of a positive ELISA/negative WB from a pregnant woman in our ID clinic just a couple of weeks ago. No-one batted an eyelid - she was HIV-negative, simple as that. You're preaching to the choir. Cheers Bennett > > Actually, the explanation is very simple. You are confusing positives > > and false positives. [quoted text clipped - 4 lines] > Err, but by definition if the confirmation tests are negative, then the > test is negative. You mean when the confirmation test is negative, the result is negative. > A false positive would be a positive ELISA AND confirmation test, when > in fact there was no HIV present. In the context of this discussion, a false positive is a positive screening test, which is then refuted by a negative confirmation test. > > Then, you must have a clear explanation of why these 25%, 33% infection > > rates disappear as soon as testing involves non-pregnant girls in Africa. [quoted text clipped - 4 lines] > The article you quote from gives you that answer. It's simply that the > 32.5% of girls who were tested in the early years GREW OLDER. And this cured them of HIV? What happened, is that a different survey type was used, nothing more. The 32.5% is based on the Antenatal Clinic Survey, which tests about 200 or so pregnant women at antenatal clinics, which are usually in urban settings. On the other hand, the survey that showed that only 6% of girls tested positive, was part of a DHS survey, which routinely tests the blood of 10,000 statistically representative people. In other words, the test subjects are selected on their representativeness of the general population. And obviously, most of these girls who were tested weren't pregnant. That is the difference. Now if only HIV Insite would get clued up to this fact. Alex > > > Actually, the explanation is very simple. You are confusing positives > > > and false positives. [quoted text clipped - 6 lines] > > You mean when the confirmation test is negative, the result is negative. Correct. By 'test is negative' I meant 'the result of the test is negative'. > > A false positive would be a positive ELISA AND confirmation test, when > > in fact there was no HIV present. > > In the context of this discussion, a false positive is a positive screening test, > which is then refuted by a negative confirmation test. You can redefine concepts all you like to support your argument, but by definition a positive screen/negative confirmation is a negative result, not a false positive. The HIV test is a multi-step process. > > The article you quote from gives you that answer. It's simply that the > > 32.5% of girls who were tested in the early years GREW OLDER. > > And this cured them of HIV? No, read the bloody article. The 32.5% of girls UNDER 19 turned into the 35-40% of women OLDER than 19 in the more recent study. I quote: **** The study was prompted by the results of the government's 2002 sero-surveillance study, which estimated that 32.5 percent of teenage girls between the ages of 15 and 19 were HIV-positive. ...... Nevertheless, the new baseline survey found a 40 percent HIV-prevalence rate among older girls, from 19 years upwards, which matched the sero-surveillance study results. **** Tada! In summary - In 2002 32.5% of girls aged 15-19 were thought to be HIV+ (based on antenatal screening) In 2004 6% of girls aged 15-19 tested HIV+, with a big difference between 18 and 19 (i.e. mostly older kids). In 2002 AND 2004 women aged 19+ (whether antenatally screened or systematically studied) were just under 40% HIV+ So it doesn't take a degree in epidemiology to guess that most of the HIV burden in 2002 was in women who are now older than 19 years... In fact the current study put the 12-18 year old prevalence at only 4%. If the methods used in each study were so fundamentally flawed then why does the rate in women older than 19 stay roughly the same? You're comparing apples and oranges. The 32.5% rate in the 2002 teenagers was an estimate anyway, not a direct measurement, but also the paper clearly states that there appears to have been a change around 2001 in sexual attitudes and behaviours, with a reduction in the rate of first-time sex prior to age 18. This quite possibly explains a change in seroprevalence, as you would expect dealing with an infectious (and not a ubiquitous environmental) cause of positive test results. Cheers Bennett And just another thing: > http://womenshealth.about.com/cs/aidshiv/a/aidshivwomen_2.htm > A reactive test may give a false positive reading to anyone with kidney > or renal failure, to a woman that has had multiple pregnancies, anyone > receiving the influenza vaccine, or to anyone that has received gamma > globulin. So what is it exactly, that is making an ELISA false positve under these circumstances, and how does it do that? Alex > And just another thing: > [quoted text clipped - 6 lines] > So what is it exactly, that is making an ELISA false positve > under these circumstances, and how does it do that? Renal failure - not sure about this one but some reports put it at ~5% prevalence in screening of dialysis patients. The only primary reference provided in the bible of all "false positive results" (Christine Johnson's article) was withdrawn by the authors about 6 months later. A literal handful of case reports and series exist in the literature. In those cases where the ELISA is positive but the WB is negative and the antigens are investigated, it appears to be cross-reactions to antigen-presenting proteins on white blood cells probably due to multiple blood transfusions. May not be as important today with the widespread usage of leukodepleted blood tranfusions but I don't think anyone has checked,. Pregnancy - under 1% with many modern tests but very race-dependant. Likely due to activation of endogenous RV's and antibody formation to them (we know this happens, I just don't know if anyone has proven that these particular antibodies cross-react with HIV ELISAs). Flu vaccine - one batch of one year's dose from one manufacturer reacted with some older ELISAs (in fact one component of the test kit, not any of the viral antigens in the test kit). It was probably due to weirdness in how that batch of vaccine was made. Not likely to be relevant today. IVIG (intravenous immune globulin) - simply put, massively high doses of non-specific antibodies will cause false positive results on many antibody tests, HIV included. The large amount of poorly-binding antibody looks similar to small amounts of highly-specific antibody. If you wait for the IVIG to leave the system the test results return to normal. Not really relevant. Any other questions? Cheers Bennett > > So what is it exactly, that is making an ELISA false positve > > under these circumstances, and how does it do that? [quoted text clipped - 34 lines] > > Bennett Sure, and thanks for the substantive answers. I was thinking of what makes these tests false positive on a basic level. http://www.biology.arizona.edu/immunology/activities/elisa/technique.html? According to this website, ELISA HIV antibody testing works as follows: 1) Partially purified, inactivated HIV antigens pre-coated onto an ELISA plate Patient serum which contains antibodies. 2) If the patient is HIV+, then this serum will contain antibodies to HIV, and those antibodies will bind to the HIV antigens on the plate. 3) Anti-human immunoglobulin coupled to an enzyme. This is the second antibody, and it binds to human antibodies. 4) Chromogen or substrate which changes color when cleaved by the enzyme attached to the second antibody. So my question is, what exactly goes wrong during this procedure, that a woman's pregancy can cause a false positive test result? What (if anything) is attaching to the HIV antigens to cause a false positive? Alex > So my question is, what exactly goes wrong during this procedure, > that a woman's pregancy can cause a false positive test result? What > (if anything) is attaching to the HIV antigens to cause a false positive? Sigh! You can lead a horse to water and all that... Read Bennett's post (#3) again...... Go to the explanation he gave you 6 years ago...... (http://groups.google.com/group/misc.health.aids/msg/135f320fc95ac5a6) If there are circulating antibodies to these retroviral fragments in maternal serum, then when an HIV ELISA is performed they may bind to one or more of the HIV antigens used in the assay, causing a biological false positive reaction. Also give this paper a read - it goes through many of the issues under discussion here. http://archfami.ama-assn.org/cgi/reprint/9/9/924.pdf You must appreciate that false positive results are rare, and not the norm, as denialists would have us believe. In this paper, you will see the false positive prevalence in 5 million blood donors was 0.0004% (1 in a quarter of a million). http://jama.ama-assn.org/cgi/reprint/280/12/1080?ijkey=2cd06a67709f4496110866e75 24d856c70a9f380 This also has good explanations about the PPV questions you have.
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