In the summer of 1981, the first AIDS cases, although they weren't called that then, were reported in San Francisco. Young men were presenting with rare diseases typical of immune suppression, and they were dying. Although no one knew it at the time, these first cases of AIDS signal that for many years before, HIV had been spreading unchecked through the population of men who have sex with men in San Francisco, and in fact most corners of the world. The people investigating the outbreak tried to work out what the risk factors were, and the film and a band played on tells that story. The 1980's saw the number of deaths due to AIDS grow and grow. The HIV virus was then characterized and a test for HIV was developed. So blood samples were tested. It became clear HIV was everywhere and already reaching very high levels, among in particular women that sold sex in parts of East Africa. The peak number of deaths at two million per year have been likened to 18 Jumbo jets full of passengers crashing every single day. But from the late 1990's, we saw the introduction of a life-prolonging treatment and from there, reductions in the number of deaths in high income settings. As it's been rolled out elsewhere, since about 2003, we've seen AIDS deaths decrease there as well. I'll talk more about HIV treatment in the next lecture. HIV incidence, which is the rate of new infections, has also overall stabilized since the mid 1990's. At a global level, you can see a gradual decline in HIV incidence, but of course, we'll want incidence to be much lower, and that's what that doc shows. That's the UN AIDS target for new infections by 2020. We'll look at targets later on too. So here is how the world looks today for HIV prevalence, just the proportion of adults living with HIV. You can see the epidemic has hotspots in South America, Asia, Eastern Europe, and here the epidemics has had to be concentrated, because it's mostly people that have a high risk for HIV in this key populations that are affected. But the epicenter of the epidemic is Africa. But Africa has a lot of variation within it too. In West Africa, the epidemic is mostly among sex workers. But the epidemics in East and Southern Africa are different. There are sometimes called generalized epidemics. Here the spread of HIV is so great that it seems that everyone has a risk of becoming infected. You'll explore this data in more depth yourself. But for now, remember that these global trends obscure three important points. First, that there is substantial variation in HIV prevalence within countries. New data show the countries tend to have hotspots at cities or road intersections. This is because the behaviors that support HIV transmission can be tied to places more strongly than say the behaviors that support influenza transmission. Second, if you're in a key population, you have a high risk of infection whereever you are. These maps of HIV prevalence show that for the case of sex workers and men who have sex with men. Third, you can't see it, but there have been success stories, HIV incidence has been substantially reduced in several settings. Look at these graphs from Uganda and Thailand. In each case, we are seeing reductions in HIV incidence. In the case of Uganda, which has a generalized epidemic, we think that people came to have fewer sexual partners, which reduced HIV transmission. In this graph, you can see HIV prevalence among young women in a clinic in West Uganda reducing over time, which must have been due to reduce risk for infection. There was a broad public health campaign, and it also seems that people were acutely aware of the risk of HIV from having seen so many of their friends, neighbors, and family members die of AIDS. In Thailand, which has a construct epidemic and higher risk of transmission among, from, and to sex workers, there was a program introduced whereby sex workers had to use condoms much more, which we think led to less transmission. Here you can see HIV prevalence among military conscripts in successive cohorts reducing, which must be indicative of HIV infection risk reducing over time. Now, in fact, these reductions have not always been maintained, but they still give us important clues into how the tide can be turned against HIV more decisively at a global scale, and you'll be focusing on that in the next lecture. In summary, the HIV epidemic came from nothing in the early 1980's to exact a terrible toll on human life in AIDS deaths. AIDS deaths have reduced, thanks to the treatment although needs to be done. But HIV incidence has broadly settled at quite a high level. So next, we shall look at treatment and then prevention in much more detail.
