AIDS testing

Reposted from the old TfK.

Two recent comments on the 25th anniversary of AIDS took up a similar call, one in the New England Journal of Medicine, the other from Scienceblogger Tara Smith.

Both essentially argue for the broadening of HIV testing in American society. The NEJM piece largely recycles the history of debates about testing for HIV in the general population, and state limitations on what testing can be mandated. Tara explains:

Currently, the testing paradigm in most areas is patient-instituted, and involves the three C’s: consent, confidentiality, and counseling (generally before and after the test). If HIV testing were increased, a concern is that the quality of counseling could decrease, due to the lesser availability of trained professionals to discuss the implications of the test with patients. This could leave individuals whose test came back positive for HIV floundering, unsure what to do next, how to receive treatment or protect their loved ones from infection (or discuss that possibility with them), and unversed in dealing with the stigma that may follow a diagnosis of infection with HIV.

For these reasons, it’s unlikely that any kind of universal testing will occur anytime soon.

When it was found that prenatal treatment with anti-retrovirals could decrease the chance of mother to child transmission, some states instituted mandatory pre-natal screening, but even that didn’t spread. The stigma of HIV/AIDS is too great, and before the disease could be controlled effectively the testing was too close to a death sentence to make it mandatory.


As the NEJM points out, this sort of exceptionalism is no longer merited in an age where treatment for HIV/AIDS can extend lives for decades after an early diagnosis.

There’s another case for change, one that is as true now as it was 25 years ago. Controlling the spread of the disease requires the standard tracing of sexual partners that’s commonplace with syphilis and other STDs. Such mandatory screenings, matched with appropriate treatment and counseling before and after, could drastically cut the spread of HIV in society.

There is, however, a good argument against universal mandatory screening – excess false positives. In the course of an unrelated discourse a while back, I explained it as follows:

If you pick a random person off the street and test for HIV, a positive result is most likely not an undiagnosed case of HIV, but a false positive. For instance, the standard ELISA test used for HIV gives a false positive only 1 in 67 times. There are 300 million people in the US, and about a million are HIV+. If we tested everyone, we’d get 4.5 million false positives, meaning that the chances of someone with a positive test result actually being sick would be less than 1 in 5.

There are two things that make the testing that actually happens more accurate. First, every positive ELISA is verified with a second test, one that is more expensive and complex. ELISA catches 99.7% of true HIV+ cases, and sweeps up some extra. The second test weeds out that extra part. Average cost is held down by only testing likely cases.

The second thing that makes ELISA accurate is that it’s not mandatory. We don’t apply it at random, it’s applied to people who think they are at risk. The fraction of HIV+ people among those who engage in risky activity is greater than the proportion of HIV+ people in the population at large, so the number of false positives decreases.

In the comments to that post, I was asked about Washington, DC’s program to test every resident of the District. I replied:

The argument there is that, since 1 in 50 DC residents have AIDS, even more are HIV+. Even with a 1.5% false positive rate, your odds of actually being HIV+ given a test result remain high when the rate of infection in the population may well be above 3%. In a sense, the argument would be that living in DC is itself a risk factor.

Nationally, the infection rate is around 0.76%. At that rate, a positive test result is twice as likely to be a false positive as a real positive. At five times that infection rate, the odds are better than 2:1 that a positive result is an actual infection.

Mandatory testing will leave a lot of people in fear and confusion, unless the testing is done with tremendous care and and careful explanations. Telling 3 million people they might be infected when they aren’t will cause mass panic, and to no good end. We need an end to exceptionalism, but not through universal screening. Universal screening itself would be exceptional. What we need is to treat HIV like other STDs, remove the veil of secrecy enough to implement effective partner notification and testing. The ACLU has listed some serious privacy and effectiveness concerns with such programs, but also suggests ways that programs of partner tracking could be made more effective.