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An MUHC team evaluates a new saliva-based HIV test to speed up detection

May 06, 2008

The usual waiting period for the results of a HIV test can seem like an eternity, especially in emergency situations where results are needed immediately. Also it requires a blood sample, which is invasive and often painful. Recognizing the urgent need for a faster and less invasive diagnostic method, Dr. Nitika Pant Pai, from Marina Klein's research team at the MUHC has just finished testing a new saliva-based test that gives results in approximately 20 minutes! She describes her findings in an article that will appear in the May 6th, 2008 issue of PLoS Medicine (Public Library of Science, an open access publication).

To overcome the barriers associated with blood collection, which is off-putting for many patients, this new test is based on oral mucosal transudate (OMT), a fluid that is secreted at the base of the gums before it becomes saliva. In fact, the level of antibodies in OMT is comparable to that of blood plasma, making it an excellent sample.

To test this innovative technique under real world conditions, especially in vulnerable pregnant women, Dr. Pant Pai carried out clinical trials in the labor ward of the Mahatma Gandhi Institute of Medical Sciences, Sevagram, Maharastra, India. "In such cases, it is vital to determine the HIV status of the mother very quickly to prevent transmission to the child during delivery. Many Indian women do not receive prenatal care and therefore do not get tested for HIV during pregnancy. Testing in the labor ward is the last chance to prevent HIV transmission to the newborn baby. Also Indian patients often refuse blood collection, while saliva collection poses no problem," explained Dr. Pant Pai.

This is the kind of situation when this innovative test reveals all its potential. In the study, 1222 mothers were tested for HIV in the labor ward using both saliva and blood samples. The results from both kinds of tests corresponded in 100 percent of cases. In addition, use of the saliva test in the labor ward helped identified several HIV infected women who were unaware of the HIV status. These women received treatments to reduce the chance of HIV infection in the newborn babies. This is an incredible piece of evidence for the accuracy and ease of execution of this new oral test.

The underlying method, called immunochromatography, is the same as for pregnancy tests. This technique aggregates the antibodies contained in the sample of oral mucosal transudate with the antigens (molecules recognized as enemy by the immune system) contained in the test. The OMT is simply collected on a stick, which is also similar to the one used in a pregnancy test, and then placed in a small tube containing a special solution. Between 20 and 40 minutes later a purple line will appear at the top of the stick if the result is positive.

"Rapid saliva tests are not in use yet in Canada, as they are met here with a lot of skepticism," Dr. Pant Pai acknowledged. "However, their efficacy has now been demonstrated for all subtypes of HIV-1 and HIV-2." These tests could become highly useful for vulnerable or at-risk people who are not always given adequate medical follow-up. A rapid, low-cost test would therefore reduce the number of patients who are unaware of their HIV status.

Long-term, this research will hopefully pave the way to a more widespread use of rapid oral fluid HIV tests to prevent mother to child transmission of the HIV virus. It may also pave the way for an over-the-counter test for home use.

McGill University Health Centre