Tuesday, August 7, 2012
Someone who has posted helpful and perceptive comments on this blog in the past has suggested that I am too much of a 'doubting Thomas' about 'treatment as prevention' as a strategy. So it's worth setting out some of the reasons for my skepticism. Treatment as prevention calls for putting anyone found to be HIV positive on antiretrovirals (ARV) immediately, rather than waiting until they have reached a clinical stage at which these drugs are currently considered appropriate.
Actually, there are too many arguments against treatment as prevention for me to do justice to in a short blog post. So I'll try to keep to arguments that do not require levels of in-depth technical knowledge that I cannot claim to have.
The various stages of HIV infection will be familiar to those who have spent a little time reading up on the subject. The first stage, which only lasts for a few weeks, may pass unnoticed. People going through the primary stage can be very infectious but it is unlikely that they will have any reason to take a HIV test and even if they do, the result may not be positive.
The second stage is said to last for an average of 10 years and during this time HIV positive people are not usually very infectious, which is not to say that they are not infectious at all. But if their HIV status is confirmed, there are tests that can be carried out to gauge the progression of the virus throughout this stage.
At the third stage, the symptomatic stage, various opportunistic infections emerge. Those who receive and respond to treatment in time remain asymptomatic. If they don't receive treatment or if they don't respond to treatment, HIV leads to AIDS, the fourth stage of infection. Those whose CD4 cell count and viral load are being monitored are more likely to receive ARVs in time.
So where does treatment as prevention come in? It's unlikely to have much impact on people going through the first stage as most infections will not have been detected. Those going through the second stage already have a low viral load, so it is both unnecessary and harmful to put them on a lifelong course of drugs; unnecessary because most will not be very infectious and many of those who know their status will already be taking precautions to avoid infection; harmful because there are short and long term side effects relating to ARV treatment and, perhaps more importantly, because resistance to first line ARVs is often just a matter of time, especially in resource poor countries, where monitoring and other resources are poor.
The time for treatment as prevention has generally passed once people go from the second to the third stage because ARVs would already be appropriate by then. Having said that, people in resource poor countries may have to wait a long time to receive treatment and many will die, either despite the treatment or because they never receive treatment. Some developing countries are only able to treat a minority of those who have reached the appropriate clinical stage for treatment and many have only managed to test a minority of HIV positive people.
So even if resource poor countries were to be granted the health services they need to provide HIV positive people with the treatment and care they need, it's not clear where a strategy like treatment as prevention would fit in. On top of that, it's not even clear that putting more people on treatment would be a good thing, unless they have already reached the appropriate stage of infection.
An early version of the treatment as prevention strategy was called 'test all, treat all' (and various other things) because it advocated the regular testing of everyone (or about 80%) in a population and the immediate treatment of those found to be HIV positive. But the emphasis on testing everyone at regular intervals may have been quite a stumbling block. Has any country achieved universal testing, let alone persuaded a large percentage of the population to return for re-testing every year or so?
I am all for treatment, so I would like to see the millions of HIV positive Africans receiving it when it is appropriate. But the consequences of trying to treat everyone, regardless of what stage of infection they have reached, are not well understood. To the extent that they are understood, they are very serious; treatment as prevention is a clear commercial imperative, but it has not been demonstrated to be beneficial in countries with serious HIV epidemics.
As for other arguments against treatment as prevention, there are plenty of articles and blogs on the subject. There's one on some of the problems that such a strategy may have in Zambia if it is scaled up. Dr Joseph Sonnabend has discussed the subject on several occasions. And it has even been debated by people for whom commercial imperatives may be expected to hold considerable sway. There is even solid evidence that there are viable alternatives to HIV prevention strategies such as treatment as prevention that would have a far greater impact on broader health issues than HIV alone.
My critic concludes that treatment as prevention is worth investigating, and I agree. Just as long as those investigating it do not see their task as one of manufacturing evidence for the benefits of doling out very expensive and potentially toxic drugs to as many people as possible. We need to find ways of preventing HIV infection in those who will otherwise soon be seen as potential recipients of treatment as prevention, rather than waiting for them to be infected and then jumping in to 'prevent' any further infections.
Perhaps primary prevention has not been very successful because we have been concentrating on the wrong risks, obsessing about the sexual risks rather than acknowledging that not all HIV is sexually transmitted. Treatment as prevention simply propagates the myth that 80% or more of HIV transmission in African countries is sexually transmitted. We need to find out more about who is being infected and how, rather than assuming that we already know. There may then be a role for expensive and limited strategies like treatment as prevention. But we haven't got there yet.
[For more about non-sexual HIV transmission, see the Don't Get Stuck With HIV site.]