History and size of HIV/ADS - a global perspective: Prof Michael Adler

Professor Michael Adler MD FRCP FFPHM Professor of GU Medicine/STDs, University College Medical School, London

AIDS was first recognised, even though not called this, in 1981, when clusters of cases of Pneumocystis carinii pneumonia and Kaposi's sarcoma were reported in the USA. HIV was discovered in 1983 at the same time as the first cases of this infection were seen in Europe.

In 1984, a new antibody test was developed that allowed for more detailed epidemiological descriptions of the epidemic.

Transmission of the virus

Globally, approximately 80% of all HIV infection is transmitted through sexual intercourse, vaginal intercourse being the commonest way that the virus is spread. Other common routes of transmission are from mother to child in the womb, at birth and through breast milk, through contaminated blood, injecting drug use and sharing of needles and equipment.

Size of the problem

The World Health Organisation estimated that, at the end of 1997, there were 30.6 million adults and children living with HIV/AIDS. The majority of these are in Sub-Saharan Africa (20.8 million) and South and South-East Asia (6.8 million). The WHO also estimated that, during 1997, 5.8 million new HIV infections occurred - approximately 16,000 per day - and that deaths due to HIV and AIDS were approximately 2.3 million.

The epidemiology varies considerably between the developed and developing world, but also within the developed world. So in Sub-Saharan Africa and South and South-East Asia, for example, the main mode of transmission is through heterosexual intercourse, whereas in the USA and UK it is through homosexual intercourse. In some other European countries, such as Italy and Spain, HIV is most commonly transmitted by the sharing of injecting equipment by intravenous drug users.

Rates of infection in certain risk groups in the developing world are high, so in some countries, for example, the level of infection in prostitutes can reach 80% and in other groups that are not necessarily high risk, such as women attending antenatal clinics, the rates may be as high as 35-40%. Currently, in the UK, there are 15,000 cases of AIDS and approximately 30,000 of HIV infection.

The epidemic in the UK, as mentioned previously, has been seen mainly in homosexual men, so that 70% of the cases of AIDS have occurred in this particular group, 15% as a result of heterosexual intercourse and 7% as a result of sharing needles and equipment.

The UK epidemic is slowly changing, with proportionally more infections occurring amongst heterosexuals. The level of infection in pregnant women is low, but in certain parts of central London is just under 0.5%.

Factors associated with the spread of HIV

Interventions to reduce transmission between adults

In the developed world there is now a well-established therapy that can cut down vertical transmission considerably. However, it is expensive and therefore not freely available in the developing world.