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Spread of AIDS
Sunday, February 1, 2009/ 12:53 AM
Spread of AIDS
HIV is spread sexually, through contaminated blood, and from mother to child. The virus is present in semen, both as free virus and in infected cells, and in vaginal secretions of infected people, and can be transmitted by either homosexual or heterosexual intercourse. The probability of a woman becoming infected during unprotected vaginal intercourse with an infected male is estimated at less than 1/50. The risk of a man becoming infected during heterosexual intercourse is less. The risk is much higher if genital lesions resulting from sexually transmitted diseases are present. The risk of infection is also much higher during receptive anal intercourse. The use of condoms reduces the risk of transmission considerably.
The virus can also be spread by means of contaminated blood, whether through blood transfusions, the use of contaminated products by haemophiliacs, by needle stick in health care workers, the sharing of needles by injecting drug users, or via tattoo needles. Blood transfusion was an important source of infection before the development of test for the virus and remains a problem in developing countries where blood tests may not be regularly available. Similarly, many hemophiliacs became infected before the development of blood tests. Use of blood tests and screening of donors for risk factors have greatly reduced the risk of transmission of HIV through blood products in developed countries. However, transmission among drug users remains an important source of infection.
Untreated, infected women transmit the virus to a newborn child about one-fourth of the time. Transmission can occur during delivery or during breast feeding. The use of anti-HIV drugs has reduced transmission to infants in countries where the drugs are available.
At the end of 1999, an estimated 43 million people were living with HIV/AIDS, with about 1 million of those in North America. The cumulative death toll from AIDS since the beginning of the epidemic reached 20 million in the first half of 2000. More than 5 million new infections occurred worldwide in 1999, and about 5.4 million people died of AIDS that year. In the absence of treatment, virtually all infected people go on to develop AIDS and die within 2 years of the appearance of the symptoms of AIDS.
At the end of 1999, an estimated 43 million people were living with HIV/AIDS, with about 1 million of those in North America. The cumulative death toll from AIDS since the beginning of the epidemic reached 20 million in the first half of 2000. More than 5 million new infections occurred worldwide in 1999, and about 5.4 million people died of AIDS that year. In the absence of treatment, virtually all infected people go on to develop AIDS and die within 2 years of the appearance of the symptoms of AIDS.
The focus of HIV infection is sub-Saharan African, where25 million people, or more than 5% of the population, are thought to be infected and where medical care is still primitive. In the 15 years from 1984 to 1999, the number of HIV infections increased dramatically. The extent of the problem is illustrated by the fact that in some large cities in sub-Sahara Africa, an estimated 20-40% of adults may be infected. The spread of HIV has resulted in a marked decrease in life expectancy, which has reversed a long period of increasing life expectancy as health care standards have improved. In other areas of the world, HIV continues to spread but has not reached the extreme levels found in parts of Africa.
In Latin America and in southern and southeast Asia, about 0.6% of the population is infected. In North America, western Europe, and Australia, estimates are that 0.3% of the population is infected. In North America, HIV has been spread primarily through homosexual contacts and by sharing needles by drug users who inject drugs, but the frequency of heterosexual transmission is increasing. In developing countries, heterosexual contact is the primary mode of transmission.
In the United States, the number of newly diagnosed cases of AIDS, especially in white homosexual men, has dropped because awareness of the disease has led to the more frequent use of condoms and a lowered incidence of multiple sex partners, and because more effective drug therapies have been introduced.
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