Transmission of human immunodeficiency virus (HIV) by blood transfusions screened as negative for HIV antibody

Immunological features of human immunodeficiency virus disease

Infection with the human immunodeficiency viruses results in a profound immunosuppression responsible for most of the clinical features of AIDS. The virus devastates the immune system because its main target is the T4 lymphocyte, which is the key component for generating and regulating the immune response. The cellular receptor for HIV, the membrane glycoprotein CD4, is found mainly on the surface of this major subpopulation of T lymphocytes and also on many other cell types such as those of the monocyte/macrophage series. HIV can destroy CD4 cells by direct virus cytotoxicity and indirectly through the host response against HIV-infected cells or gp120-targeted cells. Cells of the macrophage lineage are generally not destroyed but serve as a reservoir of virus. HIV also causes functional impairment in T cells, B cells and monocytes. The virus can exist in latent or chronic form. The mechanisms of cellular destruction, viral persistence and conversion to a productive infection are being studied vigorously. Host factors that may affect clinical outcome and immunological markers that may predict progression of HIV disease are presently delineated. Prolonged serological latency may follow infection with HIV. Protective humoral and cell-mediated immune responses to HIV are either poor or not sustained. Recent results on HIV-specific cytotoxic T lymphocytes are of great interest. These cytotoxic cells, particularly those directed to gp120 targets, probably contribute to cellular damage. A central question regarding immunity to HIV is its beneficial versus deleterious effects, particularly in regard to the eventual development of an AIDS vaccine.

Efficacy and safety of predeposit blood autodonation in 500 cases of myocardial revascularization

Since 1985 all patients scheduled for coronary artery bypass grafting have been evaluated for admission to a program of predeposited blood autodonation. From a total of 816 consecutive patients, 505 were admitted to the program (group 1). The other 311 (group 2) were excluded on the basis of one or more of the following criteria: 1) emergency surgical indication, 2) hemoglobin less than 12 g/dl, or 3) uncontrolled angina or clinically manifest cardiac failure. Postoperative use of homologous blood products was required by 16% of the group 1 and 44% of the group 2 patients (p less than 0.001). Altogether 597 patients (73%) had no contact with homologous blood products. There was no intergroup difference in the incidence of postoperative complications. Non-A, non-B hepatitis developed in three group 1 and four group 2 patients. Its incidence was 0.9% among all discharged patients and 3.2% of the homologous blood recipients. The findings emphasize the safety and value of the autodonation with predeposit program in significantly reducing the requirement for homologous blood in coronary artery bypass grafting.

Current status of clinical laboratory tests for the human immunodeficiency virus

The predictive values of positive and negative test results for human immunodeficiency virus (HIV) antibody are extremely high in laboratories that have good quality control and high performance standards and use licensed FDA-approved enzyme immunoassay (EIA) and Western blot standardized tests. With a carefully designed protocol, the false-positive rate of combined EIA and Western blot has been reported to be as low as 1 in 10(5). When results of HIV confirmatory antibody tests are indeterminate, other tests such as culture and nucleotide probe methods for HIV DNA or RNA may help resolve false-reactive screening EIA tests. Improvements are constantly in progress for HIV laboratory tests with the use of recombinant DNA-derived antigens and synthetic polypeptides. With the use of new-generation synthetic polypeptide antigens, specific assays to identify HIV-1 and HIV-2 have been developed. Recently, assays for the HIV regulatory gene products have been studied for their predictive potential. Antibodies to nef protein, a regulator of HIV-1 replication, may be an early indicator of HIV infection.

Blood-product usage in cardiac surgery

Many patients undergo cardiac surgery with preexisting congenital and acquired coagulation defects. Almost all of these can be recognized and corrected preoperatively. CPB itself induces a variety of abnormalities of coagulation, affecting plasma proteins, platelets, and the fibrinolytic system. These abnormalities do not always cause clinically significant bleeding. When they do, logical laboratory assessment and blood-component usage can usually correct the defect. The use of blood products is associated with allergic, viral, and hemolytic risks. Exciting advances have been made in the use of synthetic alternatives to blood products. Both DDAVP and aprotinin seem promising in this respect, but more investigation is needed into the mechanisms of action and possible thrombotic complications of these drugs. In the future, anesthesiologists and surgeons may look forward to more safe and effective therapy of bleeding in cardiac surgical patients.

Exposure of patients to human immunodeficiency virus through the transfusion of blood components that test antibody-negative

The risk of transmission of the human immunodeficiency virus to recipients of blood transfusions exists chiefly during the period between the time a donor is infected and the time he or she has a positive blood test for HIV antibodies. Estimating the chance that blood will be donated during this period is an effective way to define the risk of HIV infection from transfusion. Using this approach, and employing data from over 17 million American Red Cross blood donations, we estimate that during 1987 the most likely number of units of blood infected with undetected HIV that were transfused was 131 (range, 67 to 227). For a patient, the odds of contracting HIV infection were 1:153,000 per unit transfused. A patient who received the average transfusion (5.4 units) had odds of 1:28,000. The risk has been decreasing by more than 30 percent a year. We estimate that donor-recruitment practices plus careful education and screening are eliminating 49 of every 50 donors likely to be HIV-positive and that testing is 92 to 97 percent effective, for a combined effectiveness of 99.9 percent. The risk of undetected infectious units can probably be further reduced by transfusing fewer units and units from fewer donors, recruiting more women and fewer men as new donors, and encouraging more frequent donations from donors who have been tested repeatedly.

Clinical implications of positive tests for antibodies to human immunodeficiency virus type 1 in asymptomatic blood donors

Of 693,000 volunteer blood donors in Washington, D.C., who were screened for infection with human immunodeficiency virus type 1 (HIV-1) from July 1985 through December 1988, 284 tested positive on both enzyme immunoassay and Western blot assay. To determine the clinical importance of confirmed positive test results in asymptomatic blood donors, we followed 156 donors with positive Western blot assays and 80 donors with positive enzyme immunoassays but negative or indeterminate Western blots at 6-month intervals for a mean of 28 months. As compared with Western blot-negative persons, those with positive Western blots were significantly more likely to be black, male, and first-time donors and to have a history of venereal disease, generalized lymphadenopathy on examination, CD4-cell counts lower than 0.4 x 10(9) per liter, IgG levels higher than 18 g per liter, and antibody to hepatitis B core antigen on initial evaluation. In 17 (11 percent) of the Western blot-positive donors, the disease progressed to Class IV (symptomatic disease), according to the Centers for Disease Control system. CD4 counts below 0.2 x 10(9) per liter, IgA levels above 4 g per liter, abnormal proliferative responses to tetanus toxoid, and positive viral cultures were the strongest predictors of disease progression. Among the 80 donors with repeatedly reactive assay results but either negative or indeterminate Western blot assays, there was no evidence of HIV exposure in their histories, physical examinations, or laboratory evaluations, and manifestations of HIV infection developed in none of them. We conclude that a small number of persons with HIV infection continue to donate blood, despite attempts to exclude them, but that donors who test positive on enzyme immunoassay but persistently negative or indeterminate on Western blot assay probably do not represent a risk for the transmission of HIV.

The natural history of transfusion-associated infection with human immunodeficiency virus. Factors influencing the rate of progression to disease

Patients infected by the human immunodeficiency virus (HIV) as a result of blood transfusions are unique in that their dates of infection are well defined and their medical conditions before infection are known. To characterize the natural history of transfusion-associated HIV infection, we studied 694 recipients of blood from 112 donors in whom AIDS later developed and from 31 donors later found to be positive for HIV antibody. Of the recipients tested, 85 were seronegative, 116 were seropositive, and 19 had AIDS. Of 101 HIV-seropositive recipients followed for a median of 55 months after infection, 54 had Centers for Disease Control Class IV disease, including 43 with AIDS. Life-table analysis suggested that AIDS will develop in 49 percent of infected recipients (95 percent confidence limits, 36 to 62 percent) within seven years after infection. As compared with recipients without AIDS, the 43 recipients with AIDS had received more transfusions at the time of infection (median, 21 vs. 7; P = 0.01). HIV-infected blood donors in whom AIDS developed were grouped according to whether AIDS developed within 29 months (the median) after donation (Group 1) or 29 or more months after donation (Group 2). As compared with the 31 recipients of blood from Group 2 blood donors, the 31 recipients of blood from Group 1 donors were more likely to have AIDS four years after infection (49 percent vs. 4 percent; P = 0.005) and illnesses resembling acute retroviral syndrome (14 of 24 vs. 5 of 22; P = 0.03). We conclude that most recipients of HIV-infected blood become seropositive, that AIDS develops in about half these recipients within seven years, and that the risk may be higher when AIDS develops in the blood donor soon after donation.

Detection of HIV genome in HIV antibody negative men

The presence of the human immunodeficiency virus (HIV) genome was investigated by applying in situ hybridisation techniques to peripheral blood mononuclear cells (PBMCs). Twenty asymptomatic anti-HIV seronegative homosexual men were the subjects of our study. The cells were hybridised with: (1) an SP 64 plasmid containing the nine-kilobase SstI-SstI viral insert from the lambda BH 10 recombinant clone; this can recognise both viral RNA and proviral DNA, and (2) with a pA01 plasmid containing HBV DNA genome. The DNA probes were modified by inserting an antigenic sulfone group in the cytosine moieties and the visualisation was performed by a double antibody immunohistochemical reaction. In two subjects both the HIV genome and HBV DNA were detected whereas another two subjects were positive for HBV DNA and for the HIV genome respectively. Thus people who are seronegative for anti-HIV specific antibodies may be infected with HIV.

Acquired immunodeficiency syndrome: more than a health-related dilemma

Many legal issues will affect the health care worker during the AIDS pandemic. These issues are now beginning to be contested in our courts. It is certain that their numbers will continue to grow in the foreseeable future. As local, state, and federal governments design and implement new laws concerning PWA, mechanisms for surveillance, and control of AIDS, new issues are sure to arise. These will undoubtedly involve persons concerned with providing service to those afflicted with this illness. The direction of health care research has already been altered by AIDS. Societal relationships have been affected, as evidenced by the increasing number of legal charges filed when the question of HIV infection involves a patient, student, employee, or other citizen. Inevitably, the health care worker who has contact with PWA will be asked to participate in the mechanisms of the resulting legal contests. If the case reports cited above are an indication of the legal struggles ahead, appearance as a witness to provide scientific information as well as information about the care and treatment afforded PWA will be required of health care workers with increasing frequency.

Duration of human immunodeficiency virus infection before detection of antibody

To estimate the duration and frequency of the period of HIV infection without detectable antibody, modelling techniques were applied to results of detection of HIV DNA by means of the polymerase chain reaction (PCR) and to data from cases in published reports. PCR was carried out with gag and env region primers on samples from 27 homosexual and 12 haemophilic men for whom stored samples were available from before and after seroconversion; serum was also tested for p24 antigen by antigen-capture enzyme immunoassay. HIV DNA was detectable before seroconversion in 4 men; in all 4 PCR was positive only in the seronegative sample taken closest to the time of seroconversion. In 3 men antigen was detected before seroconversion; in each case HIV DNA was also detected. By a Markov model, the time from infection with HIV (as assessed by detection of HIV DNA) to first detection of HIV antibody was estimated to be 2.4 (SE 2.1) months for the median individual. Modelling of cases of HIV infection with known exposure in published reports gave a median estimate of 2.1 (0.1) months from exposure to antibody detection, and 95% of cases would be expected to seroconvert within 5.8 (0.6) months. HIV infection for longer than 6 months without detectable antibody seems uncommon.

Minimizing the use of homologous blood products during repair of abdominal aortic aneurysms

The recent threat of post-transfusion AIDS and increased awareness of blood-related hepatitis have compelled surgeons to minimize the use of homologous blood products during aortic aneurysm repair. Reducing or eliminating homologous blood transfusion can be achieved by aggressive attention to three aspects of patient care: (1) routine use of autologous transfusion; (2) careful surgical technique, emphasizing the minimum dissection needed to expose the aneurysm adequately; and (3) a higher threshold for use of any blood products. In a prospective study of 100 consecutive aortic reconstructions, 80 per cent of patients undergoing aneurysm repair received only their own blood during hospitalization. Routine intraoperative autologous red-cell salvage has also conserved the bank blood supply by reducing usage of homologous blood by 75 per cent. The key to minimizing homologous blood requirements for aneurysm repair has been the development of rapid cell-washing autotransfusion devices.

HIV genome in peripheral blood mononuclear cells of seronegative regular sexual partners of HIV-infected subjects

We have investigated the presence of the human immunodeficiency virus (HIV) by using in situ hybridization on peripheral blood mononuclear cells (PBMCs) from seronegative regular sexual partners of HIV-infected subjects. The cells were hybridized with a 9 kilobase (kb) Sstl-Sstl lambda BH 10 probe, which was able to recognize both viral mRNA and proviral cDNA. Labeling was done by chemical insertion of an antigenic sulfone group in cytosine moieties and was visualized by a double-antibody immunohistochemical reaction. In all the subjects studied, the HIV genome was present. The HIV infected cells showed morphological aspects consistent with that of lymphocytes and monocytes. Our data suggest that the anti-HIV seronegative individuals who are regular sexual partners of HIV-infected subjects may be HIV-infected.

Antigen detection for human immunodeficiency virus

The recent development of enzyme immunoassay procedures for the direct determination of human immunodeficiency virus (HIV) antigens has been of significant benefit in both clinical and research applications. The historical development of HIV antigen assays as well as their current and future applications for use in the clinical microbiology laboratory are reviewed. A detailed description of selected commercially available assays is presented, and a comparison is made of various parameters, including sensitivity, specificity, and cost. The use of the HIV antigen assay as an alternative to the reverse transcriptase assay in virus culture applications is also discussed. In addition, the diagnostic and prognostic utility of the HIV antigen assay is considered for various patient groups, including neonatal, high-risk asymptomatic, seronegative, and seropositive patient populations. The use of the HIV antigen assay as an adjunct to anti-HIV antibody testing, as well as its utility in assessing the therapeutic efficacy of antiviral drug therapy, is discussed. The biology of HIV antigen expression and modulation of anti-HIV antibody titers during infection are also discussed in terms of two possible models.

Statistical analysis of the stages of HIV infection using a Markov model

We use a staged Markov model to estimate the distribution and mean length of the incubation period for acquired immunodeficiency syndrome (AIDS) from a cohort of 603 human immunodeficiency virus (HIV) infected individuals who have been followed through various stages of infection. The model partitions the infected period into four progressive stages: (1) infected but antibody-negative; (2) antibody-positive but asymptomatic; (3) pre-AIDS symptoms and/or abnormal haematologic indicator; and (4) clinical AIDS. We also model a fifth stage: death due to AIDS. The estimated mean (median) waiting times in each stage of infection are stage 1, 2.2 (1.5) months; stage 2, 52.6 (36.5) months; stage 3, 62.9 (43.6) months; and stage 4, 23.6(16.3) months. We estimate the mean AIDS incubation period (from infection to development of clinical AIDS) as 9.8 years with a 95 per cent confidence interval of [8.4, 11.2] years. The paper also considers the estimated density function of the AIDS incubation period and the estimated survival functions for individuals in each stage of infection. This work represents one of the most complete statistical descriptions to date of the natural history of HIV infection.

Evaluation of three enzyme immunoassays for HIV-1 antigen detection

Three enzyme immunoassay (EIA) methods for the detection of human immunodeficiency virus (HIV-1) were evaluated. Serum or plasma samples from 22 individuals seropositive for HIV-1 antibodies were tested with the Abbott, Coulter, and DuPont kits for presence of HIV-1 p24 antigen. Another 12 samples were tested with two kits only. Discordant results were obtained with 9 of 34 (26%) HIV-1-antibody-positive patient samples tested. Most of these discrepancies were found in samples containing less than 30 pg/ml of HIV-1 p24 core antigen. A sampling of sera from normal blood donors and patients with infectious or autoimmune diseases revealed a low level of false positive reactions, especially with sera containing antinuclear antibodies or rheumatoid factor. Noteworthy is the frequency of false positive reactions seen with the DuPont EIA for HIV-1 p24 antigen. 18/111 sera (16.2%) containing auto-antibodies tested positively with the DuPont HIV-1 p24 antigen EIA. The nonspecific nature of the test reactivity for 9/10 of these samples was confirmed using an HIV-1 p24 antigen inhibition assay. These findings are discussed in light of the need for HIV-1 antigen detection in the clinical laboratory and of other methods for HIV-1 detection: the polymerase chain reaction and measurements of reverse transcriptase activity.

Epidemiology of human immunodeficiency virus infection and acquired immunodeficiency syndrome

As of December 31, 1988, 82,764 cases of acquired immunodeficiency syndrome (AIDS) and more than 46,000 AIDS-related deaths had been reported in the United States. In 1987, AIDS deaths accounted for 9% of the total mortality among men 25 to 34 years of age. Projections suggest that the impact of human immunodeficiency virus (HIV) infection on morbidity and mortality in young adults and children will continue to increase, with an estimated 50,000 cases projected to be diagnosed in 1989. The mean latency period between infection and diagnosis of AIDS is estimated to be more than seven years, and 78% to 100% of persons infected with HIV are predicted to develop AIDS within 15 years of onset of infection. Rates of seroconversions have been decreasing since 1984 among cohorts of homosexual HIV-seronegative men, and the proportion of AIDS cases among homosexual men is decreasing. In contrast, the proportion of AIDS cases attributed to intravenous drug use is increasing, with 33% of AIDS cases reported in 1988 occurring among intravenous drug users, their sex partners, or children of women who are intravenous drug users or sex partners of intravenous drug users. Worldwide, the differences in the epidemiology of HIV infection and AIDS are primarily due to differences in the proportions of the modes of transmission and in the time in which HIV infection was introduced.

Safety and use of autologous blood donation during the third trimester of pregnancy

To examine autologous blood donation during the third trimester of pregnancy, records of 272 blood donors who donated by standard procedures were reviewed. The incidence of vasovagal reactions at autologous donation was 2.1% (7/341) versus 1.1% (1370/121,539) at homologous donation (p = 0.17). Follow-up was available for 199 of these donors and 10 additional donors with fetal monitoring. Infant morbidity and mortality rates were not higher than expected; 0.5% (1/214) was stillborn. Although 11% (24/209) of deliveries was associated with autologous transfusion, only 4.3% (9/209) would have had a hemoglobin level less than 8 gm/dl without transfusion. Patients with placenta previa had the highest incidence of transfusion, 83% (5/6). Transfusion incidence was higher for women donating within 1 week of delivery, 21% (8/38), versus 9.4% (16/171) for women donating earlier in pregnancy (p = 0.044). We recommend that donation be completed by 2 weeks before the estimated date of confinement to allow for recovery of red cell mass.

Health education and the AIDS epidemic

What is known about the biology of AIDS is reviewed, and the social factors which influence disease transmission and public attitudes are considered. After an evaluation of the methods available to control the epidemic, the reasons for the limited success of public health measures thus far undertaken are considered. The ethical debate on public health policy is analysed, and the need for a nationwide educational programme on AIDS is emphasised--one which is responsive to the rights and obligations of citizens in a democratic society.

Antibodies to the nef protein and to nef peptides in HIV-1-infected seronegative individuals

The silent period that follows infection by the human immunodeficiency virus (HIV-1) and precedes seroconversion remains a problem for the screening of blood supply, and knowledge about the mechanism involved in the maintenance of latency is only fragmentary. Using purified nef recombinant protein and six synthetic nef peptides, antibodies to the product of an HIV-1 regulatory gene, the negative regulatory factor (nef) involved in maintenance of proviral latency, were detected by Western blot and radioimmunoassay techniques in HIV-1-seronegative, viral antigen-negative, and virus culture-negative individuals at risk for HIV infection. This antibody response to nef was correlated in eight individuals with the detection of HIV-1 proviral DNA by oligonucleotide hybridization, following enzymatic amplification of HIV DNA in peripheral blood mononuclear cells. Such latent HIV infections have now been followed for up to 6 or 10 months in five individuals. In addition, retrospective and prospective analysis of HIV-1-seropositive individuals have shown (1) antibodies to nef preceding seroconversion, and (2) the persistence of antibodies to nef and of HIV-1 proviral DNA in a case of spontaneous complete HIV-1 seronegativation. Since DNA amplification cannot be currently considered for routine use, screening for anti-nef antibodies followed by confirmation by DNA amplification could represent a basis for new diagnostic strategies. Beyond their diagnostic implications, these findings, suggesting that regulatory genes of the HIV-1 provirus can be expressed prior to the initiation of virion synthesis, may also be applicable in the design of alternative vaccines against the acquired immunodeficiency syndrome.

Blood conservation in cardiac surgery. Preliminary results with an institutional commitment

To evaluate the effect of blood conservation in cardiac surgery, use of blood products was analyzed in patients undergoing CABG before and after implementation of blood conservation techniques. Age, sex, coronary anatomy, ejection fraction, cardiopulmonary bypass time, and the preoperative hematocrit, platelet count, and clotting studies were similar in both groups. Methods of blood conservation included autologous transfusion of blood withdrawn before bypass, autotransfusion of shed mediastinal blood, strict protocols for transfusion, and acceptance of normovolemic anemia. With blood conservation, 25.5% of patients received no transfusions and 54.9% received blood only. Significant reductions (p less than 0.001) were achieved in the transfusion of blood from 6.8 +/- 2.4 to 2.3 +/- 2.6 units per patient and of plasma from 2.5 +/- 2.2 to 0.6 +/- 2.0 units per patient. Reductions in the use of platelets and cryoprecipitate were substantial, although not significant. Total donor exposure was reduced significantly from 13.1 +/- 7.3 to 4.3 +/- 6.7 donors per patient. The postoperative hematocrit was significantly lower and remained so at discharge. However, 30 days later there was no difference. This reduction in transfusion requirements decreased costs and donor exposure.

Transmission of retroviruses by transfusion of screened blood in patients undergoing cardiac surgery

We determined the rates of seroconversion to human immunodeficiency virus type 1 (HIV-1) and human T-cell leukemia virus Type I (HTLV-I) in a cohort of patients receiving transfusions of blood components screened for antibody to HIV-1. Preoperative and postoperative serum samples were collected from 4163 adults undergoing cardiac surgery who received 36,282 transfusions of blood components. The postoperative samples from all patients were tested for serologic evidence of HIV-1 infection, and those that were positive were compared with the corresponding preoperative samples. One case of HIV-1 transmission by transfusion of screened blood components was identified; two preexisting HIV-1 infections were found. Samples from 2749 patients were tested similarly for serologic evidence of HTLV-I infection; these patients received 20,963 units of blood components. Five new cases and two preexisting cases of HTLV-I infection were detected. The observed risk of HIV-1 transmission by transfusion was 0.003 percent per unit; the risk of HTLV-I transmission was 0.024 percent per unit. We conclude that there is a very small risk of HTLV-I infection from transfused blood products that have been screened for antibodies to HIV-1, but that it is nearly 10-fold higher than the risk of HIV-1 infection.

Human immunodeficiency virus and acquired immunodeficiency syndrome: correlation but not causation

AIDS is an acquired immunodeficiency syndrome defined by a severe depletion of T cells and over 20 conventional degenerative and neoplastic diseases. In the U.S. and Europe, AIDS correlates to 95% with risk factors, such as about 8 years of promiscuous male homosexuality, intravenous drug use, or hemophilia. Since AIDS also correlates with antibody to a retrovirus, confirmed in about 40% of American cases, it has been hypothesized that this virus causes AIDS by killing T cells. Consequently, the virus was termed human immunodeficiency virus (HIV), and antibody to HIV became part of the definition of AIDS. The hypothesis that HIV causes AIDS is examined in terms of Koch's postulates and epidemiological, biochemical, genetic, and evolutionary conditions of viral pathology. HIV does not fulfill Koch's postulates: (i) free virus is not detectable in most cases of AIDS; (ii) virus can only be isolated by reactivating virus in vitro from a few latently infected lymphocytes among millions of uninfected ones; (iii) pure HIV does not cause AIDS upon experimental infection of chimpanzees or accidental infection of healthy humans. Further, HIV violates classical conditions of viral pathology. (i) Epidemiological surveys indicate that the annual incidence of AIDS among antibody-positive persons varies from nearly 0 to over 10%, depending critically on nonviral risk factors. (ii) HIV is expressed in less than or equal to 1 of every 10(4) T cells it supposedly kills in AIDS, whereas about 5% of all T cells are regenerated during the 2 days it takes the virus to infect a cell. (iii) If HIV were the cause of AIDS, it would be the first virus to cause a disease only after the onset of antiviral immunity, as detected by a positive "AIDS test." (iv) AIDS follows the onset of antiviral immunity only after long and unpredictable asymptomatic intervals averaging 8 years, although HIV replicates within 1 to 2 days and induces immunity within 1 to 2 months. (v) HIV supposedly causes AIDS by killing T cells, although retroviruses can only replicate in viable cells. In fact, infected T cells grown in culture continue to divide. (vi) HIV is isogenic with all other retroviruses and does not express a late, AIDS-specific gene. (vii) If HIV were to cause AIDS, it would have a paradoxical, country-specific pathology, causing over 90% Pneumocystis pneumonia and Kaposi sarcoma in the U.S. but over 90% slim disease, fever, and diarrhea in Africa.(viii) It is highly improbable that within the last few years two viruses (HIV-1 and HIV-2) that are only 40% sequence-related would have evolved that could both cause the newly defined syndrome AIDS. Also, viruses are improbable that kill their only natural host with efficiencies of 50-100%, as is claimed for HIVs. It is concluded that HIV is not sufficient for AIDS and that it may not even be necessary for AIDS because its activity is just as low in symptomatic carriers as in asymptomatic carriers. The correlation between antibody to HIV and AIDS does not prove causation, because otherwise indistinguishable diseases are now set apart only on the basis of this antibody. I propose that AIDS is not a contagious syndrome caused by one conventional virus or microbe. No such virus or microbe would require almost a decade to cause primary disease, nor could it cause the diverse collection of AIDS diseases. Neither would its host range be as selective as that of AIDS, nor could it survive if it were as inefficiently transmitted as AIDS. Since AIDS is defined by new combinations of conventional diseases, it may be caused by new combinations of conventional pathogens, including acute viral or microbial infections and chronic drug use and malnutrition. The long and unpredictable intervals between infection with HIV and AIDS would then reflect the thresholds for these pathogenic factors to cause AIDS diseases, instead of an unlikely mechanism of HIV pathogenesis.

Protecting the blood supply

Prevention of the transmission of the acquired immunodeficiency syndrome (AIDS) by transfusion has been the most successful area of epidemiologic control of the disease. Only 2% of the more than 50,000 cases reported to the Centers for Disease Control (CDC) have been attributed to transfusion, and the vast majority of these patients were infected before the introduction of screening tests in April 1985. The overall prevention program involves donor education, adequate medical history, physical examination, and mechanisms that allow exclusion of individuals at risk in a confidential manner. The current screening tests for human immunodeficiency virus (HIV) antibodies are highly sensitive, and the Western blot confirmatory test is highly specific. The present program can be used as a model in screening for other viruses and diseases, and its success has stimulated current work in developing multiple-retrovirus screening tests to detect either several retroviruses simultaneously or elements that are common to all retroviruses.