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Current Trends Human T-Lymphotropic Virus Type I Screening in Volunteer Blood Donors -- United States, 1989

On November 29, 1988, the Food and Drug Administration (FDA) issued recommendations to screen all whole blood donations in the United States for human T-lymphotropic virus type I (HTLV-I) (1). This report summarizes results of the first 13 months of screening (December 1988 through December 1989) by the American Red Cross (ARC) and the Council of Community Blood Centers (CCBC).

HTLV-I was the first human retrovirus discovered. The virus is endemic primarily in southwestern Japan and the Caribbean but also is endemic in parts of sub-Saharan Africa and Central and South America (2). HTLV-I is transmitted by blood transfusion and contaminated needles, by sexual contact, and from mother to child through breastfeeding. The virus is associated with two diseases: a hematologic malignancy known as adult T-cell leukemia/lymphoma and a degenerative neurologic disease named HTLV-I-associated myelopathy or tropical spastic paraparesis (2). The latter disease has been associated with blood transfusion (3).

Human T-lymphotropic virus type II (HTLV-II), the second human retrovirus discovered, is closely related to HTLV-I and is presumably transmitted via the same mechanisms. Recent reports suggest that HTLV-II is present in intravenous-drug users (IVDUs) (4,5). HTLV-II has not been consistently associated with any diseases.

In 1988, the FDA licensed enzyme-linked immunoassays (EIAs) as screening tests for antibody to HTLV-I (1). Repeatably reactive specimens are confirmed by investigational Western blot and radioimmunoprecipitation assays. Serum specimens demonstrating reactivity against HTLV-I gag p24 and env gp46 or gp68 are considered seropositive. Because serologic tests, including the confirmatory assays, do not distinguish between antibodies to HTLV-I and HTLV-II, seropositivity to HTLV-I is frequently referred to as seropositivity to HTLV-I/II. Additional tests, such as polymerase chain reaction (PCR) and synthetic peptide assays (6), are required to differentiate the two viral infections.

Of 6.4 million donations screened by the ARC from January 1 through December 31, 1989 (data for the first month of screening are unavailable), 4225 (0.066%) were repeatably reactive by EIA, and 902 (0.014%) (approximately 21% of repeatably reactive specimens) were confirmed as seropositive for HTLV-I/II (Table 1, page 921). Of 2.8 million donations screened by blood banks affiliated with the CCBC from December 1, 1988, through December 31, 1989, 5005 (0.18%) were repeatably reactive by EIA, and 604 (0.021%) (approximately 12% of repeatably reactive specimens) were confirmed as seropositive. Seropositivity rates by region varied considerably but were highest in the Pacific region (Alaska, California, Hawaii, Oregon, and Washington) in both the ARC and the CCBC systems (Figure 1, page 922).

More detailed data regarding HTLV-I/II-seropositive donors have been compiled by the ARC (ARC, unpublished data). Among 485 seropositive donors, the percentages of black females (33%), black males (10%), Hispanic females (9%), Hispanic males (6%), Asian females (2%), and Asian males (2%) were all higher than the estimated proportion of these groups in the overall ARC donor population (4%, 6%, 2%, 2%, less than 0.5%, and less than 0.5%, respectively). In addition, possible risk factors for HTLV-I/II seropositivity included a history of IV-drug use (20% of males, 4% of females), sexual contact with an IVDU (2% of males, 29% of females), birth in or sexual contact with a person from the Caribbean (23% of males, 17% of females), birth in or sexual contact with a person from Japan (13% of males, 6% of females), and a history of blood transfusion (13% of males, 11% of females). With the exception of history of blood transfusion, which was more prevalent in seropositive than in seronegative donors, frequencies of these other potential risk factors in the overall donor population, or in a suitable control group, are unavailable.

PCR studies were performed on peripheral blood mononuclear cells from the first 136 HTLV-I/II-seropositive ARC blood donors available (ARC, unpublished data): 56 (41%) were confirmed to be infected with HTLV-I, 57 (42%) with HTLV-II, and three (2%) with both viruses. In 20 (15%) donors, no evidence of HTLV-I or HTLV-II infection was detected. In general, HTLV-I infection correlated with being from or having had sexual contact with persons from the Caribbean or Japan; HTLV-II infection correlated with history of IV-drug use or history of sexual contact with an IVDU. About half of the infected donors reporting a history of blood transfusion as a risk factor were infected with HTLV-I, and about half with HTLV-II. Reported by: AE Williams, PhD, CT Fang, PhD, MT Sullivan, MS, American Red Cross, Rockville, Maryland. J Starkey, Council of Community Blood Centers, District of Columbia. AI Chernoff, MD, American Association of Blood Banks, Arlington, Virginia. JS Epstein, MD, TP Gross, MD, Laboratory of Retrovirology, Div of Transfusion Science, Center for Biologics Evaluation and Research, Food and Drug Administration, Rockville, Maryland. Retrovirus Diseases Br, Div of Viral and Rickettsial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Of approximately 13 million units of blood donated in the United States each year, about half are donated through the ARC and about one quarter through blood banks affiliated with the CCBC. The remainder are donated through community and hospital blood banks. Therefore, the findings in this report reflect approximately three quarters of the blood donated in the United States.

HTLV-I/II seropositivity in units donated to the ARC and the CCBC was 0.014% and 0.021%, respectively. These rates are similar to those for human immunodeficiency virus (HIV) (7) and are only about 10% of those for hepatitis C virus (8), suggesting that the prevalence of HTLV-I/II infection in the U.S. population is low. Decreased HTLV-I/II seropositivity rates in both the ARC and the CCBC systems, particularly in the last quarter of 1989 (Table 1), reflect the exclusion of blood donors who test positive.

Differences in HTLV-I/II seropositivity between the ARC and the CCBC systems (Table 1) and both within and between regions (Figure 1) probably reflect characteristics of the specific populations included in each system. Both systems report the highest rates from the Pacific region; for the CCBC, this observation reflects in part the inclusion of Hawaii, which has a substantial number of Japanese-American blood donors.

Findings from the ARC suggest that females and blacks, Hispanics, and Asians are more likely to be HTLV-I/II-seropositive than males and whites, respectively. Potential risk factors for seropositivity also include Japanese and Caribbean ancestry, history of sexual contact with persons from Japan and the Caribbean, IV-drug use, and history of sexual contact with an IVDU. Such risk factors are consistent with current knowledge concerning HTLV-I and HTLV-II, but the prevalence of these possible risk factors in the overall donor population is unknown.

Because of the low prevalence of HTLV-I/II seropositivity in the blood donor population, the positive predictive value of a repeatably reactive screening test (i.e., the percentage of reactive tests that confirm as HTLV-I/II-seropositive) is low in both blood systems, emphasizing the need for confirmatory testing of EIA-reactive specimens (9). Therefore, persons should not be informed that they are infected with HTLV-I/II unless screening-test reactivity is confirmed by supplemental tests (1,10). The reasons for reactive screening tests in specimens that do not confirm as HTLV-I/II-seropositive are unknown; in rare cases, repeat testing of these specimens, or testing of specimens obtained later from the same person, demonstrate seropositivity for HTLV-I/II. Cross-reactivity with HIV does not occur when licensed screening tests are performed properly.

The limited PCR data suggest that approximately half of HTLV-I/II-seropositive donors are infected with HTLV-I, and half with HTLV-II. Based on PCR analysis, a low percentage of seropositive donors were not infected with either virus. Although this finding could indicate that these donors are not infected, it more likely reflects limitations of the sensitivity of the technique, because fewer than one in 100,000 cells may be infected with HTLV-I and HTLV-II in asymptomatically infected persons (CDC, unpublished data). A serologic test capable of differentiating HTLV-I from HTLV-II would be helpful for counseling purposes, since HTLV-II has not been consistently associated with any diseases. Peptide assays that distinguish between antibodies to HTLV-I and HTLV-II are under investigation (6).

Since tests for distinguishing HTLV-I from HTLV-II are not routinely available, blood donors and others confirmed to be seropositive for HTLV-I/II are counseled as though they were infected with HTLV-I. In addition to being informed of HTLV-I disease associations, they should be counseled not to donate blood or other organs, not to share needles, and not to breastfeed infants. Counseling regarding sexual behavior must be individualized and should take into account such factors as number of sex partners, age and serologic status of a monogamous sex partner, and the likelihood that an infected sex partner will develop disease if infected (10).


  1. CDC. Licensure of screening tests for antibody to human

T-lymphotropic virus type I. MMWR 1988;37:736-40,745-7.

2. Blattner WA. Retroviruses. In: Evans AS, ed. Viral infections of humans: epidemiology and control. 3rd ed. New York: Plenum Medical Book Co., 1989.

3. Osame M, Janssen R, Kubota H, et al. Nationwide survey of HTLV-I-associated myelopathy in Japan: association with blood transfusion. Ann Neurol 1990;28:50-6.

4. Lee H, Swanson P, Shorty VS, Zack JA, Rosenblatt JD, Chen ISY. High rate of HTLV-II infection in seropositive IV drug abusers in New Orleans. Science 1989;244:471-5.

5. Kwok S, Gallo D, Hanson C, McKinney N, Poiesz B, Sninsky JJ. High prevalence of HTLV-II among intravenous drug abusers: PCR confirmation and typing. AIDS Res Hum Retroviruses 1990;6:561-5.

6. Lippka JJ, Bui K, Reyes GR, et al. Determination of a unique and immunodominant epitope of human T cell lymphotropic virus type I. J Infect Dis 1990;162:353-7.

7. CDC. National HIV seroprevalence surveys--summary of results: data from serosurveillance activities through 1989. Atlanta: US Department of Health and Human Services, Public Health Service, 1990; DHHS publication no. (CDC)HIV/CID/9-90/006:16-20.

8. Menitove JE, Richards WA, Destree M. Early US experience with anti-HCV kit in blood donors (Letter). Lancet 1990;336:244-5.

9. Khabbaz RF, Hartley TM, Lairmore MD, Kaplan JE. Epidemiologic assessment of screening tests for antibody to human T-lymphotropic virus type I (HTLV-I). Am J Public Health 1990;80:190-2. 10. Kaplan JE, Khabbaz RF. HTLV-I: newest addition to blood donor screening. Am Fam Physician 1989;40:189-95.

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