A WAY of rapidly tracking the spread of HIV will allow health workers to focus prevention campaigns on people and in places where the risk of infection is highest. Such a method has been sought for many years.
鈥淭his is a significant advance,鈥� says Roy Anderson, an epidemiologist at Imperial College, London, who wants the UK to start using the method. 鈥淚t鈥檚 very useful in tracking trends.鈥�
With existing antibody tests you can work out how many people in a population are infected at any one time. But until now only a series of these tests could reveal how fast the virus is spreading and in which groups it is spreading most rapidly. This kind of tracking is laborious and usually takes at least a year.
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鈥淚f we are to stop the epidemic we need to have a better understanding of where, why and how transmissions are occurring,鈥� says Bharat Parekh of the US Centers for Disease Control (CDC) in Atlanta, Georgia, who has developed a new antibody test based on existing techniques. Known as the BED-capture enzyme immunoassay, it can reveal not only if someone is HIV-positive, but also if they have been recently infected.
The test measures the fraction of total blood antibodies that target HIV, which is known to gradually rise in the two years after infection. In practice, a cut-off point is chosen to allow health workers to distinguish between people who have been infected for under six months, or for longer. This means a single round of testing can reveal how many people are infected and how many new infections there have been in the past six months.
Trials of the BED-CEIA test in Ethiopia produced results that tallied with those of conventional studies that had taken three years to complete. It has also been tried in Cambodia, Thailand and Africa.
The tracking method will be used to direct a national AIDS prevention programme for the first time, when Cambodian health officials meet later this month to discuss the results of BED-CEIA tests on thousands of stored blood samples collected between 1999 and 2002. The unpublished figures reveal that in most areas new HIV cases have been falling, which may be due to condom promotion campaigns. But in the west of the country, which borders Thailand, infection rates among women tested at pregnancy clinics have more than trebled.
Vonthanak Saphonn of the Cambodian health ministry who carried out the study, speculates this is because there is more migration in that area. 鈥淎 large mobile population may play an important role in driving this epidemic,鈥� he says.
The CDC is now looking for commercial partners to scale up manufacture of the test. A similar kind of test was developed by the CDC in the late 1990s, and validated by large trials. But it involved a lengthy dilution process that was judged impractical, especially for developing countries.
