Prevalence of antibodies to human T cell leukaemia/lymphoma virus in blood donors in north London.

OBJECTIVES: To determine the prevalence of antibodies to the human T cell leukaemia/lymphoma viruses (HTLV-I and HTLV-II) in blood donors in north London in order to assess the economic impact and the logistic effects that routine screening would have on the blood supply. DESIGN: All donations collected by the north London blood transfusion centre between January 1991 and June 1991 were screened for antibodies to HTLV-I and HTLV-II by modified, improved Fujirebio gel particle agglutination test. Positive samples were titrated and retested as necessary. SUBJECTS: 96,720 unpaid volunteers, who gave 105,730 consecutive donations of blood and plasma. SETTING: North London blood transfusion centre. MAIN OUTCOME MEASURE: Observed numbers of donors confirmed to be seropositive for HTLV by reference laboratories. RESULTS: Of 2622 (2.5%) initially reactive samples, 414 (0.4% of all samples) gave a titre of > or = 1 in 16 on the modified agglutination test. Thirty five of the 414 serum samples yielded positive results on one of two enzyme linked immunosorbent assays (ELISA (Cambridge Biotech and Abbot)), and none of these results were confirmed by either reference laboratory. Five samples yielded positive results on both ELISAs and all five of these were confirmed to contain antibodies to HTLV. One of the five contained antibodies to HTLV-II and the others antibodies to HTLV-I. Four seropositive donors were white women whose only risk factor for infection was sexual contact. The fifth (positive for antibodies to HTLV-II) was an Anglo-Caribbean man who admitted to previous misuse of intravenous drugs. CONCLUSION: The prevalence of antibodies to HTLV in blood donors in north London was one in 19,344 (0.005%). Up to 100 donors a year might be identified in the United Kingdom as being infected with HTLV, although prevalence in different regions may vary considerably.

Is there a wastage of resources due to non-specificity of anti-HIV ELISAs?

A library of anti-HIV ELISA 'grey-area' and repeatably reactive samples sent for confirmatory testing, were retested using a second technique, the modified (Fujirebio Gelatin Particle) agglutination test (MAT). On testing 224 grey-area reactive samples, only four were found to be reactive with this second test. On retesting a further 259 ELISA repeatably reactive samples, of which only 33 were confirmed to be anti-HIV-1, only 45 were reactive by MAT; these included the 33 confirmed as positive samples, thereby reducing the false-positive from 226 to 12. The introduction of this second technique supported our decision to cease the referral of grey-area samples. It also demonstrated the high prevalence of non-specificity of repeatable reactivity associated with some of the most specific ELISA kits currently available.

Anti-HIV-1: extended validation of a modified gelatin particle agglutination assay, and its use with an image analyser.

Modification of a commercial gelatin particle agglutination assay for anti-HIV-1 (MAT) has increased sensitivity, reduced reaction time and lowered the cost by 90%. We tested over 10,000 blood donations in parallel with the ELISA currently in use, and found the modified test to be highly sensitive and to enhance cost-effectiveness as it substantially reduces false-positive rates. The patterns of agglutination are clearly reproducible and readable by the naked eye and/or Image Analyzer, which provides objectivity and hard-copy documentation of results.