There are now almost 40 million people living with HIV infection, the majority in developing regions of the world. In some sub-Saharan African countries, such as Swaziland and Botswana, infection levels in young adults (15-49 years) is estimated at over 25%. Transmission is mainly through heterosexual sex. Consequences for the working population are immense if those infected with HIV become sick and die without treatment. Not only are there social and economic consequences but transmission generally occurs when people are asymptomatic or do not know that they are infected, so it is very difficult to effect change in attitudes and behaviours to prevent spread. It is essential to invest in treatment for people already infected and recent work shows that people on antiretroviral therapy will be much less likely to pass on the disease. www.unaids.org AIDS Epidemic update 2007.