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False-Positive Serologic Tests for Human T-Cell Lymphotropic Virus Type I Among Blood Donors Following Influenza Vaccination, 1992

From October 31 through December 15, 1991, 10 blood donors to the American Red Cross Blood Services, Badger Region (ARCBS) *, were found to have false-positive screening enzyme-linked immunosorbent assays (ELISAs) for antibodies to two or more of the following viruses: human immunodeficiency virus type 1 (HIV-1), human T-cell lymphotrophic virus type 1 (HTLV-I), and hepatitis C virus (HCV) (1). An investigation by the Division of Health, Wisconsin Department of Health and Social Services (WDOH), and the ARCBS indicated that the risk for false-positive reactivity was associated with antecedent receipt of influenza vaccine formulated for the 1991-92 season (1). In March 1992, the ARCBS began use of newly available ELISAs for anti-HIV (HIVAB, HIV-1/HIV-2 (rDNA) EIA {Abbott Laboratories, ** Abbott Park, Illinois}) and anti-HCV (HCV 2.0 ELISA {Ortho Diagnostic Systems, Raritan, New Jersey}), while continuing to test with the ELISA for anti-HTLV-I {HTLV-I ELISA (Abbott Laboratories) used in 1991. From January 1 through October 13, 1992, the ARCBS identified 19 blood donors with repeatedly reactive ELISAs for HTLV-I. However, from October 14 through November 10, 15 false-positive ELISAs for HTLV-I were reported by the ARCBS to the WDOH. As a result of this increase, the ARCBS conducted a case-control study to assess the relation between influenza vaccination and testing positive for HTLV-I. This report summarizes the results of the study.

A case-donor was defined as a donor of blood to the ARCBS during the study period who had repeatedly reactive ELISAs for HTLV-I on a single donated specimen that were unconfirmed for anti-HTLV-I on supplemental assays including Western blot (WB) assay. During the study period, there were 15 case-donors; anti-HTLV-I WB assay was negative for 11 and indeterminate for four. No case-donor had a reactive ELISA for HIV-1 or HCV. Thirty control-donors who had been randomly selected from donors of blood during the study interval were seronegative for all viral serologic tests.

During November 20 through November 23, 1992, the 15 case-donors and 30 control-donors were interviewed regarding receipt of influenza, tetanus, measles- mumps-rubella, hepatitis B, rubella (single antigen), poliomyelitus, and pneumococcal vaccines during the 12 months before their donation of blood during the study interval. Donors acknowledging receipt of a vaccine were questioned regarding date of vaccination. Twelve case-donors reported they had been vaccinated against influenza before index donation, compared with two control-donors (odds ratio=56; 95% confidence interval {CI}=6-704). Among the 12 case-donors who had received influenza vaccine, 11 had negative WB assays for HTLV-I, and the mean time between influenza vaccination and blood donation was 15 days (range: 5-26 days). The intervals for the two control-donors who received influenza vaccine were 15 and 20 days.

Review of 397 blood-donation records randomly sampled from records of the 12,221 donors of blood to the ARCBS during the study period indicated that 15 (3.8% {95% CI=2.0%-5.7%}) blood donors reported antecedent receipt of influenza vaccination during the 12 months before blood donation. Based on these findings, an estimated 244-696 persons who donated blood during the study period may have been vaccinated against influenza before blood donation. Because 12 case-donors received influenza vaccination this season before blood donation, an estimated 1.7% (12 of 696) to 4.9% (12 of 244) of blood donors who recently received influenza vaccination before blood donation will have false-positive ELISAs for HTLV-I.

Reported by: BS Zarvan, AJ Hibbard, MD, G Becker, MD, American Red Cross Blood Services, Badger Region, Madison; JP Davis, MD, State Epidemiologist, Div of Health, Wisconsin Dept of Health and Social Svcs. Epidemiology Activity, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: The findings in this report indicate that false-positive ELISA reactivity for antibody to HTLV-I among blood donors in the Badger Region was associated with antecedent receipt of 1992-93 influenza virus vaccine (IVV). When July/August was compared with October/November, the proportion of blood donors with false-positive HTLV-I antibody screening tests more than doubled (0.032% to 0.083%) (American Red Cross National Reference Laboratory for Infectious Diseases, unpublished data, 1992). Because review of blood-donation records underestimates the actual number of blood donors vaccinated against influenza, the findings in this report probably overestimate the actual incidence of false-positive ELISAs for HTLV-I among influenza vaccine recipients.

The association between recent IVV and temporary false-positive ELISAs for antibodies to multiple viruses was first described in 1991 (1). Because IVVs are sterile suspensions, there is no risk of contracting any viral infection from these vaccines (2). The false-positive reactivity for antibodies to HIV, HTLV-I, and hepatitis C in association with influenza vaccination observed in 1991 has been attributed to serum immunoglobin M (IgM) (which is not specific for these viruses) binding to and cross-reacting with test kit components (3).

In early 1992, ELISA test kits for HIV and hepatitis C used in blood banks were replaced by new kits that appear to reduce -- and may eliminate -- nonspecific IgM cross-reactivity. However, similar changes have not yet been implemented for HTLV-I test kits. Consequently, although there was no recurrence of a seasonal increase of multiple false-positive viral screening tests among blood donors in the Badger Region in the fall of 1992, the findings in this report suggest a small percentage of blood donors who were recently vaccinated against influenza had false-positive anti-HTLV-I screening tests during the 1992-93 influenza season.

In accordance with an American Red Cross directive, Red Cross blood centers in the United States notify a blood donor with a repeatedly reactive ELISA for HTLV-I antibody and an indeterminate or positive WB assay. These donors are indefinitely deferred from blood donation. Blood components from a donor who has a repeatedly reactive ELISA for HTLV-I antibody and a negative WB assay are discarded, but the donor remains eligible for future blood donation if subsequently donated blood is negative by the anti-HTLV-I ELISA. If any subsequent blood donation is ELISA-reactive for HTLV-I antibody, the blood donor is notified and indefinitely deferred from blood donation regardless of the WB assay result. Because the duration of false HTLV-I reactivity following influenza vaccination is likely to be less than 4 months, the risk of false reactivity occurring during subsequent blood donations is less likely. Efforts to decrease the false HTLV-I reactivity for influenza-vaccinated donors are under way.


  1. MacKenzie W, Davis JP, Peterson DE, Hibbard AJ, Becker G, Zarvan

BS. Multiple false-positive serologic tests for HIV, HTLV-I, and hepatitis C following influenza vaccination, 1991. JAMA 1992;268:1015-7.

2. ACIP. Prevention and control of influenza. MMWR 1992;41(no. RR-9).

3. Stramer SL, Dillender MJ, Pendy LM, Holzer TJ, Abbott Laboratories. False positive EIA reactivity in multiple blood bank screening assays is due to non-specific binding of IgM {Abstract no. S111}. Transfusion 1992;32(suppl):30S.

  • An area comprising approximately 2.5 million persons residing in parts of Illinois, Iowa, Michigan, Minnesota, and Wisconsin. ** Use of trade names and commercial sources is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.

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