Background: Since 1988, all blood donations in the United States have been screened for antibodies to human T-lymphotropic virus type I (HTLV-I). However, the sensitivity of current serologic tests for the detection of HTLV type II (HTLV-II) antibodies and the diagnostic utility of direct tests for HTLV-I and -II using polymerase chain reaction (PCR) are poorly defined.
Study design and methods: Five hundred sixty-nine HTLV-I- or -II-seropositive and 687 age- and sex-matched seronegative samples from a high-risk population at an inner-city emergency department were selected. All samples were tested with four HTLV enzyme immunoassays (EIAs), one Western blot assay and one type-specific Western blot assay, one HTLV type-specific EIA, and a research HTLV-I/II PCR kit.
Results: Sensitivity of the various EIAs ranged from 95.1 to 99.5 percent, and specificity ranged from 97.2 to 99.4 percent. PCR performed in duplicate without selective retesting had lower sensitivity (85.1 %) and specificity (88.0%). However, PCR detected 20 (3.2%) HTLV-I-positive and 47 (7.5%) HTLV-II-positive samples among the 627 samples that were negative in all EIAs. The type-specific EIA and PCR assay had the highest rate of concordance in classifying samples as either HTLV-I or II, with the type-specific EIA and type-specific Western blot having the next highest rates of concordance.
Conclusion: In this sample set from a population at high risk for HTLV-II, screening with HTLV-I/II PCR had lower sensitivity and specificity than that with EIAs. However, 4.1 to 10.8 percent of samples were PCR positive but seronegative for HTLV-I or -II, and their true infection status remains undetermined.