Researchers first identified and described Acquired Immune Deficiency Syndrome (AIDS) in 1981. Since that time, more than 70,000 Americans have been diagnosed with the disease, which has no known cure.

As of July 31, more than 39,000 people in the United States had died from AIDS and AIDS-related conditions, according to the Atlanta-based Centers for Disease Control (CDC).

The CDC estimates that by 1991, as many as 10 million people in this country will be infected with the AIDS-causing Human Immuno-deficiency Virus (HIV) (also known until recently as HTLV-III and LAV). Researchers estimate a large proportion of them will develop the disease.

The complexity of the virus makes progress toward a cure extremely difficult, though doctors can often treat related illnesses. Some drugs, notably AZT, have been shown to slow the progress of AIDS or its related symptoms.

The AIDS virus is carried only by bodily fluids; it spreads chiefly through sexual contact or contact with contaminated blood, as with transfusions or shared intravenous drug needles. HIV spreads only from semen to blood, vaginal fluid to blood or blood to blood. The virus does not survive long outside these fluids and cannot be transported via food, air or surfaces such as toilet seats.

Latex condoms decrease the risk of exposure to HIV if used properly; spermicidal foams can also kill the virus. Water-based lubricants make condoms less likely to break.

Other forms of sex that do not involve the exchange of body fluids reduce the risk of transmitting AIDS. Though small amounts of the AIDS virus have been found in saliva, there is little evidence that the disease is spread through that medium.

Earlier in the history of the disease, hemophiliacs and other frequent users of the blood pool were particularly vulnerable because donors were not screened for HIV. But in 1985 the Red Cross developed a simple antibody test that virtually stopped contaminated blood from entering the pool. There is no risk in donating blood when equipment is sterile and needles are not re-used.

Health officials say their chief problem is to show people the dangers of AIDS and at the same time convince them that voluntary precautions can hold it at bay.

Ignorance about how AIDS is spread--for instance, the belief that it "selects" hosts among specific communities or ethnic groups--has in many cases hurt efforts to teach people precautions, health officials say.

And in study after study, large percentages of the public--particularly young people--also appear to have misunderstood the AIDS threat.

A recent survey showed only 3 percent of Massachusetts 16- to 19-year-olds began using condoms or abstained from sex because of AIDS--although those are the two most effective means of reducing risk. The others said they mostly became "more selective of their partners" and "careful."

Health educators say these last measures fail to address the fact that the AIDS virus is often spread via healthy carriers.

The disease is difficult to track because after the virus enters the body, antibodies may not form for three to six months--making it impossible to detect the disease in recently infected persons.

Further, symptoms may not develop until five to seven years after infection. This long, varying time period is known as the "latency" or "incubation" period. Not all those infected by HIV develop symptoms, but all who carry the virus may infect others.

This hidden spread of AIDS means that college-aged students may be another group at risk, some have suggested.

According to AIDS Education and Outreach (AEO) Directors Kevin G. Volpp '89 and Tia E. Martinez '90, college students as a whole are still among the most sexually experimental groups in society--but only a few college-aged people have been sexually active long enough for the disease to show its effects on them.

Some experts have also suggested that the rise of a new, deadly sexually-transmitted disease may force Americans to redefine old ideas about sexuality. A new definition, some say, may imply a committment to monogamy and a greater emphasis on "safer and safer" sex.