|Blood Safety and AIDS - UNAIDS Point of View (UNAIDS, 1997, 8 p.)|
The human immunodeficiency virus (HIV) is efficiently transmitted through blood transfusions. The probability of becoming infected through a transfusion of blood tainted with HIV is estimated at over 90%. (In contrast, risk through a single act of sexual intercourse ranges from a few percent to less than one percent.) And the dose of HIV in a single blood transfusion is so large that an adult infected in this way may quickly develop AIDS - on average within three to five years (two years in children).
Blood transfusions save millions of lives each year, but in places where a safe blood supply is not guaranteed, those receiving transfused blood have an increased risk of being infected with HIV.
Other diseases - such as hepatitis B, hepatitis C and syphilis - can be transmitted through transfusions. Blood transfusions can also transmit certain diseases found in tropical regions, including Chagas disease and malaria.
From whole blood, components that can be separated - such as red cells and plasma - are also widely used. Plasma products may be shared internationally, while whole blood and red cells, with a short shelf-life, are usually used nationally.
The process of testing blood to see if it contains infectious agents capable of being transmitted to those who receive the blood is known as screening. In the case of HIV, there are several types of tests.
The majority of these licensed tests detect the presence of antibodies to HIV, not the virus itself. Although anti-HIV tests, as they are known, are very sensitive, there is a window period. This is the period between the onset of infection with HIV and the appearance of detectable antibodies to the virus. In the case of the most sensitive anti-HIV tests currently recommended, the window period is about three weeks. This period may be longer if less sensitive tests are used. This means that if a unit of blood is donated by a donor within the first 21 days of becoming infected, his or her blood may give a false negative result.
Tests also exist that detect the virus itself; they are called HIV antigen tests. It is sometimes possible to detect HIV antigen during the window period if by coincidence the blood donor happens to be tested during the short peak of high levels of circulating virus particles. Although in theory the HIV antigen test can shorten the window period by an additional six days, its use is of limited value and there still remains a window of one to two weeks.
For example, out of over 6 million donated blood samples screened using HIV antigen tests in the United States of America, at an estimated additional cost of at least US$ 50 million, only a single HIV-infected sample was detected by the antigen test that was not also found by the ordinary anti-HIV test.
Several studies have shown that careful selection of low-risk donors is a more efficient way of minimizing the risk of transfusion-related infections than testing for HIV antigen. In addition, a well-functioning quality assurance programme will reduce the possibility of false-negative results resulting from technical errors. In most settings, HIV p24 antigen testing of the blood supply is not cost-effective and is not recommended by WHO.
The cornerstone of a safe and adequate supply of blood and blood products is the recruitment, selection and retention of voluntary, non-remunerated donors. Recruiting donors is not safe, practical or cost-effective unless one ensures that they are from population groups with the lowest risk of infection. However, any information obtained during the recruitment and selection of donors is strictly confidential. It must never be used as a basis for stigmatization or discrimination in the community.
Dr Jean Emmanuel, Chief, Blood Safety Unit, World Health Organization