BELIEVE IT or not, nearly 80 per cent of people in low and middle income countries seem to be just unaware that they are infected with HIV.

Not that everyone in the developed countries is aware of his/her status. That about 2.5 lakh people living in the U.S. are ignorant of their HIV positive status indicates that not everything is fine with the current detection and prevention strategies.

Keeping this ignorance in mind the Atlanta based Centers for Disease Control and Prevention had last September recommended that all patients in all health-care settings be tested for HIV. Of course, the CDC had made it clear that the testing can be done only with the consent of the individual.

The guidelines

The WHO and UNAIDS have very recently come out with similar guidelines to expand access to HIV testing to ensure that more people are detected.

And by stating that, "many opportunities to diagnose and counsel individuals at health facilities are being missed," the world bodies have come out with revised guidelines to tackle the problem. They have recommended that the HIV testing strategy be changed from the current client-initiated to a provider-initiated one. And by doing so, the world bodies have shifted the onus of getting tested from the individuals to the health care provider.

They have categorised the testing based on the prevalence of the epidemic in a country.

Today, any individual who suspects he/she is infected with HIV has to approach the voluntary counselling and testing centres (VCTC) to get tested.

Increasing detection

While the provider-initiated strategy, which will be available at all health facilities, will greatly increase the detection rate, the option to opt-out gives the individuals the choice of refusing consent to being tested. The centres will also have a facility to counsel individuals.

The high rate of detection in pregnant women due to the availability of testing in nearly all health centres is a typical example.

Any effort to make available HIV testing in more if not all health settings in the developing countries makes it almost mandatory to rely on rapid HIV testing kits.

Rapid tests, besides providing immediate results, are cheaper and require less initial investment. The need for highly trained technicians does not exist.

The gold standard in HIV testing are ELISA and Western Blot. But these two require huge initial investments, are expensive and need highly trained personnel.

Rapid tests have another advantage as well. Since the results are known immediately, the need to come back to collect the results does not arise.

The CDC had recommended rapid tests for the same reason as it found that nearly 30 per cent who tested positive and about 39 per cent who tested negative for HIV did not turn up to collect their results.

But how reliable are the rapid test kits? A paper published in the recent issue of the British Medical Journal based on a study of 1,517 males in Uganda looked at the limitations of rapid test. It states that the specificity was low in the three rapid test kits that were used. Low specificity leads to more false positives.

False positives arise when the person tests positive even when he/she is not actually infected with HIV.

The limitations

But false positives when using rapid tests are not peculiar to Uganda. The authors report that high rates of false positives had come up even when they were done in the U.S. They conclude that the problem is not restricted to specific viral subtypes.

They caution that the interpretation of rapid test results is subjective and hence person dependent. The problem of false positive, according to the authors, was more due to over-interpretation of test results.

Samples that showed weak positive bands were interpreted as positives. Retesting showed that these samples ultimately turned out to be false positives.

That the specificity increased when the technicians became cautious in interpreting test results clearly shows that reading the rapid test results is person dependent.

"We in India do not have the problem as NACO guidelines stress on quality of test kits," said Supriya Sahu, Project Director, Tamil Nadu State AIDS Control Society.. "The sensitivity is 99.5 per cent and above and specificity is 98 per cent and above."

The authors of the study recommend retesting a batch of samples using ELISA and Western Blot "to maintain quality control in programmes using rapid tests."

Routine retesting

"We [in Tamil Nadu] do 100 per cent retesting of all samples that test positive and 3 per cent of negative samples," Ms. Sahu stressed. She noted that the negative samples were picked at random.

According to her, of the 10.4 lakh samples tested last year in the State, the number of positives was 33,069 and the number of samples that turned out to be false positives when retested was nil.

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