For special purposes, it is possible to use tests in a different ways to get additional information on what is happening to the epidemic.

A good example of this is the development of 'detuned' ELISA tests to identify people who have only recently become infected with HIV.

This makes use of the observation that in the early stages of HIV infection relatively low levels of antibodies are present, which increase in quantity and quality (binding strength) over a period of months.

By taking a very sensitive test and making it less so, then using both tests on a part of each sample, it is possible to find some people who test positive on the sensitive test but negative on the less sensitive 'detuned' one. Complex maths then allow an estimate to be made of the proportion of people in a population who have seroconverted within the last year - the incidence of HIV.

This might help to identify populations where transmission is at its peak, to target HIV prevention efforts, such as help with partner notification where they are most likely to be useful.

If these tests can be validated, they might even be used to identify people whose immune system is relatively undamaged by HIV, who might benefit from early antiretroviral treatment to preserve that immune response and immunotherapy to turn it to their advantage.