Recently there has been much controversy over the exact or near exact rate of HIV infection in Papua New Guinea. Just about every HIV/AIDS prevalence study done in PNG has come out with a different result or estimate for the number of people in PNG infected with the HIV virus.
For example, a researcher based in Australia gave an estimate of the number of people in PNG infected with the HIV virus to be very high. This study was later criticised by other researchers from the PNGIMR, saying the study used mathematical models to come to those values, therefore it is NOT a true reflection of the rate of HIV/AIDS in PNG. Furthermore, there were other technical aspects of the study found to be inconsistent with standard practise.
I have been doing some reading over this very issue and wnt to share with you what is known about the HIV tests that are done in PNG. Unfortunately, the PNG public is not away of this.
How reliable is the HIV test done at the Port Moresby General Hospital?
The HIV test is done in a two stage process. Firstly, there is a screening test, called an ELISA test. At the Port Moresby General Hospital, it is known by its trade name – ImmunoComb. This is just a screening test. If you are positive, than there is a confirmatory test, called Western Blot.
The ELISA test can be positive EVEN if you are not infected with the HIV virus. These are called false positives. For every population, we need to know the false positive rate for any laboratory test. Do we know the false positive rate for the ImmunoComb HIV test kit used at PMGH? The answer is – NO WE DON’T. No study as been done, as far as I know anyway.
Now for the Western Blot test. The confirmatory test for HIV. This test is similar to the strip test that is done to check urine or the strip tests used to detect pregnancy. In this test, we check for 4 protein molecules that are supposed to be unique to the HIV virus. If the four protein molecules are present, 4 bands appear on the strip. Now the controversy is that, the criteria for saying whether you are HIV positive or not depends on the appearance of the bands. And this criteria varies from country to country.
For example, some countries in Africa use only 2 bands, some states in USA use 2 bands while some states use 3 bands to confirm that a peron is infected with the HIV virus. In Australia, you have to have all 4 bands to be confirmed HIV positive. What is the criteria for PNG? Two bands as in Africa or 4 bands or 3 bands? I don’t know.
I am pointing this out because, a major cause of the very high rate of HIV infection in PNG might be largely contributed by a rate of false positives in the screening test – ImmunoComb.
You might be asking, and what would make the screening test positive? The causes of false positives in the HIV ELISA test is almost endless. Some common examples are:
- Common cold
- Rheumatoid arthritis
- Tetanus vaccination
- Hepatitis vaccination
- Herpes Simplex I & II
- Kidney failure
- Other naturally occurring antibodies
So it seems the list is almost endless. And most likely as more studies are done, the list of causes of false positives will continue to grow.
So if this is already know, why are we continuing to use them anyway? Good question. I will leave that for you to answer.