Since 1981, when the first case of AIDS was reported in the United States, AIDS has spread all over the world and has become a major public health problem in several countries. An estimated 23 million people worldwide are reported to be living with the HIV infection. All of them will develop AIDS within the next ten years. About eighty thousand people worldwide are estimated to be infected with the HIV infection per day.

Ninety per cent of people with HIV infections are in the developing world, and of these the majority are in Sub-Saharan Africa. As per the estimates of the World Health Organisation, about thirty to forty million people all over the world will be infected by HIV by the next year and of these eight to ten million people will develop AIDS.

The first AIDS case in India was reported in 1986 from Chennai. Since then there has been a rapid spread of HIV infection all over the country. By March 1998, the National AIDS Control Organisation had reported that a total of seventy-one thousand four hundred people were having HIV infection from among 3.2 million people who were tested for it. During the same period, a total of five thousand one hundred forty-five people had been reported to have had developed AIDS. Of these, about eighty per cent were males and twenty per cent females. Almost eighty-nine per cent people with AIDS were in the age group of fifteen to forty-four years, which are the most economically productive years for any individual.

Maharashtra has reported the maximum number of HIV infections followed by Tamil Nadu and Manipur. Sentinel Surveillance reports from various parts of the country have shown varied rates of HIV infection. Sentinel surveillance involves (a) choosing a limited number of population groups and sites where these groups can be accessed and (b) testing a sample of individuals in these sites on a systematic basis, such as once in a year. Normally, sentinel groups are those where blood samples are routinely collected for some specific blood tests. During the period when the surveillance is planned, HIV testing is done for the sentinel groups in addition to the blood tests routinely done for them. This type of surveillance ensures that the blood tests can be done conveniently and anonymously. Thus, the names of the people who were tested for HIV infection are not recorded.

In India, the sentinel groups are (a)     people attending special clinics for sexually transmitted diseases, (b)     intravenous drug users and (c) pregnant women consulting with a doctor for routine check-up. The first two groups are high-risk groups for HIV and therefore give an early warning to an approaching epidemic. Epidemic is the term used for a condition where a significantly large number of people are affected with the same health problem at the same time. The pregnant women represent a general population, which is typically at lower risk, and indicates how much the epidemic has spread beyond the high-risk groups. Sentinel surveillance has indicated that 4.6 per cent to 36 per cent people attending

sexually transmitted diseases' clinics, 32 per cent to 85.6 per cent people using intravenous drugs and 0.5 per cent to 4.25 per cent pregnant women have HIV infection.