No one demands that sampling cups be treated, since people recognize that such treatment of cups will not have any impact on the expansive river. In the same way, identifying and treating persons who are found to be positive in sentinel surveillance programs will have little impact on HIV in the community. For doing such anonymous surveillance testing, saliva is an especially useful medium. Dr. Chan in his Singapore posting focused on testing done at the individual level. So there are really two purposes for diagnostic testing, one being medical and the other being public health.
Early detection is important for both.
Testing schemes have to be developed that warn HIV persons early that they are carrying the virus, and need to do something about it. Typically people first have to be screened, and then those who screen positive are given additional tests that confirm the diagnosis. Such screening and confirmatory testing can be done in the same medical setting, offering counseling and care along with testing. Here the name of the patient is known to the doctor, but the diagnosis is treated as confidential to preserve the integrity of the doctor-patient relationship. When doctors see their patients often, they can include HIV testing as a routine component of their physical examination.