False positive antibody results against human T-cell lymphotropic virus in patients with severe acute respiratory syndrome

Taiwan suffered from the outbreak of severe acute respiratory syndrome (SARS) in 2003. Our laboratory performed a series of virology and serology tests for SARS patients admitted to our hospital. Cross-reactivity was found when testing for antibody against human T-cell lymphotropic virus (HTLV) in one patient with SARS. Therefore, antibodies against HTLV were examined in paired-sera from 26 SARS patients. ELISA and a neutralization test were used to measure anti-SARS antibodies. Seroconversion for antibody against SARS-CoV was observed in all patients. Surprisingly, with the use of ELISA for HTLV, sera for 13 patients were positive for HTLV (50%), and seroconversion for HTLV was also observed in 10 patients (38.5%). Western blot for HTLV on those 26 paired-sera from 13 HTLV-positive patients displayed 5 positive results for HTLV-I, 7 positive results for HTLV-II, 1 positive result for both HTLV-I and II, 9 negative results for either HTLV-I or HTLV-II, and 4 "indeterminate" results. The findings that antibody to HTLV can be detected in blood samples collected from SARS patients provide important information for safe handling of blood products. Without such knowledge, blood products can be discarded mistakenly even though they contain anti-SARS-CoV antibodies that may be potentially valuable for SARS therapy.