HIV is known to be transmissible by blood, blood components, or plasma derivatives. The risk of contracting HIV infection from blood transfusion has been greatly reduced in the United States by implementing stringent criteria for donor acceptance, HIV antibody screening, and new methods of virus inactivation in coagulation factor concentrates. There are additional human retroviruses, however, that may pose a threat to the safety of the nation's blood supply.
The human T-cell lymphotropic retroviruses share many properties, including a preferred tropism for certain lymphocytes and similar modes of transmission. They also differ significantly from each other and on this basis are divided into two distinct groups: the human T-cell lymphocytropic viruses (HTLVs) and the human immunodeficiency viruses (HIVs). HTLV-I, a transforming virus, is the prototype of the first group (HTLVs). It is associated with adult T-cell leukemia (ATL) and is thought to be involved in a central nervous system disorder referred to as tropical spastic paraparesis. This group also includes HTLV-II, which is associated with a T-cell malignancy different from ATL. A newly isolated human retrovirus, termed HTLV-V, may be the etiologic agent of cutaneous T-cell lymphoma/leukemia, and may also be added to this group. HIV, previously known as HTLV-III or lymphadenopathy virus (LAV), a nontransforming virus, causes acquired immunodeficiency syndrome (AIDS) and is the prototype of the second group (HIVs). New members of this group of nontransforming human retroviruses were isolated from individuals in different countries of Africa. LAV-2, also referred to as HIV-2, was isolated from two AIDS patients in Africa, and the first case of AIDS in the United States caused by HIV-2 was reported in January, 1988. A third member of this group, HIV-3, was detected in Africa.
Although the HTLV family of retroviruses is distinct from the HIV family, both groups of viruses infect human T4 (CD4) lymphocytes preferentially and alter the host's T-cell functions. Whereas HTLV-I or HTLV-II primarily induce transformation and proliferation of T Lymphocytes and cause T-cell lymphoma/leukemia in humans, HIV and HIV-2 induce T-cell cytopathology that leads to depletion of CD4 cells.
The spread of HIV by blood transfusion represents a highly efficient mode of transmission. Blood components from donors with antibody to HIV have been shown to transmit the virus with frequencies of greater than 90 percent. Packed red blood cells, platelets, or fresh frozen plasma are all equally effective in transmitting the virus to recipients. It is highly likely, therefore, that recipients who receive blood from donors with antibody to HIV will themselves become infected with the virus. Fortunately, the likelihood of such an occurrence in the United States is now rare due to the implementation of screening procedures and other safeguards. When the study was initiated in 1989, there was a growing concern, however, that human retroviruses other than HIV might threaten the safety of the United States blood supply.
Blood donors were asked to participate in this multicenter study. Seropositive donors were notified of test results, counseled, and invited to join the follow-up study. Data collected during the first interview included such items as possible exposures to persons with retroviral infection, sexual preferences and contacts, marital history, intravenous drug use, occupation, travel, knowledge of AIDS and routes of HIV transmission. At subsequent visits a blood specimen was collected for laboratory testing and an assessment made of changes in behavior to reduce the risk of virus transmission.
To calculate incidence and prevalence rates, each center identified the appropriate study population for analysis purposes in collaboration with the coordinating center. For prevalence calculations, the study population consisted of donors at all centers who indicated that they had never donated blood previously. To calculate incidence, the study population consisted of donors who had donated previously in the same center. The incidence of retroviral infections was assessed annually in years three through five. Clinical follow-up of all subjects concluded 48 months after the beginning of enrollment. A blood profile for each center was required to calculate denominator values for incidence and prevalence determinations. The blood profile, or donor demographic characterization consisted of information regarding total donor volume with respect to donation status; new or repeat donor, and if repeat, the time of last donation; age; sex; and race.
An adjunct to the study was the development of repositories of plasma and cell samples from infected donors and negative controls collected at the same time. A potential byproduct of these repositories will be the ability in future years to retrospectively search the REDS frozen repository file for new retroviruses which may appear in the United States population.