Performance evaluation of Espline HTLV-I/II, a newly developed rapid immunochromatographic antibody test for different diagnostic situations

ABSTRACT Antibody screening tests for human T-cell leukemia virus type 1 (HTLV-1) are performed based on methods such as chemiluminescent enzyme immunoassay (CLEIA), chemiluminescence immunoassay (CLIA), electrochemiluminescence immunoassay, and particle agglutination (PA). Espline HTLV-I/II, a commercially available, easy-to-use, and rapid immunochromatographic antibody test (IC), was developed for situations where expensive instruments and laboratory equipment are not available. In this report, we compared the performance of IC with the above existing tests using diverse samples derived from asymptomatic HTLV-1 carriers and patients with HTLV-1-associated diseases in collaboration with 11 Japanese institutes. We found that IC detected HTLV-1 infection in all samples from HTLV-1-associated diseases, including adult T-cell leukemia, HTLV-1-associated myelopathy, and HTLV-1 uveitis (200/200). The sensitivity of IC compared with CLIA, CLEIA, and PA was 99.2% (363/366), 100% (241/241), and 100% (47/47), respectively, and the specificity was 99.4% (994/1000), 100% (60/60), and 100% (40/40), respectively. The positive and negative predictive values of IC were 99.7% [95% confidence interval (CI): 99.12–99.92] and 99.5% (95% CI: 98.82–99.75), respectively. However, IC had difficulty in correctly judging samples that were diagnosed as seroreactive in other first screening tests but negative by a confirmatory test; for example, of 612 confirmed negative samples that were CLIA seroreactive, 332 samples were IC positive. These results confirmed that IC has sufficient sensitivity and specificity as a screening test for HTLV-1, although, like the other screening tests, it also requires a confirmatory test to determine HTLV-1 infection correctly. IMPORTANCE The World Health Organization estimated that 5–10 million people are infected with human T-cell leukemia virus type 1 (HTLV-1). This number is likely to be underestimated because reliable endemic data are available for only approximately 1.5 billion people worldwide. The point-of-care test is a powerful tool for the easy and quick detection of infections without the requirement for expensive instruments and laboratory equipment. Espline HTLV-I/II, a newly developed rapid immunochromatographic antibody test that was evaluated in this study, might significantly advance our understanding of the global epidemiology of HTLV-1 infection.