How common is HTLV-III infection in the United States? [letter]

Fairly precise figures for the number of cases of the acquired immunodeficiency syndrome (AIDS) in the US are based on surveillance data gathered by the Centers for Disease Control. Since the presence of antibodies to human T-cell lymphotropic virus Type III (HTLV-III) is itself not a reportable condition and since little information is available on testing for HTLV-III antibody in the general population the number of residents of this country who have been infected with the virus is unknown. We suggest that the prevalence of this infection in the general US population as well as in identified subgroups may be estimated on the basis of existing data. The critical assumption in our calculations is that the ratio of the number of living patients with AIDS to the number of patients with HTLV-III is constant within different patient groups. To test this assumption we compared the number of living patients with AIDS with the estimated number of patients with HTLV-III in 2 well-studied populations--intravenous-drug abusers and hemophiliacs. The total estimate of hemophiliacs in this country is 14467 of whom at least 62% or 8970 may be assumed to be infected with HTLV-III according to Western blot electrophoresis. It is known that there are 31 living hemophiliacs with AIDS (Centers for Disease Control AIDS surveillance July 22 1985). Therefore for every living hemophiliac with AIDS there are approximately 289 hemophiliacs with HTLV-III. Similarly the total number of intravenous-drug abusers infected with HTLV-III in this country may be estimated to be 36% of 750000 or 270000. Since there are 923 living intravenous-drug abusers with AIDS it follows that for every intravenous-drug abuser with AIDS there are 293 abusers with antibodies to HTLV-III. A recent study revealed that this ratio was smaller in a group of homosexual men--1:30. However this group was selected on the basis of attendance at a clinic for sexually transmitted diseases and voluntary participation in the study and may not be representative of all homosexual men. If the ratio of living patients with AIDS to those with HTLV-III is approximately 1:3000 then the total number of US residents who are infected with HTLV-III can be estimated to be 1765470 (Table 1). This figure includes 64200 persons who do not belong to any identified risk group. Using currently available population data one can estimate that in the US adult population at no known risk for AIDS the prevalence of HTLV-III infection is 45/100000. A recent report from the American Red Cross indicates that the actual prevalence of HTLV-III infection calculated by screening more than 1 million units of donated blood in the general US population is 38/100000. We believe that the similarity of the calculated and actual prevalence figures supports the accuracy of our assumptions and calculations. (full text)