Anti-HIV positivity in Thailand: the usefulness of another ELISA test kit and Western blot as confirmatory tests.

Sera from 47 individuals repeatedly reactive in one screening ELISA system (designated as ELISA-A) for antibodies against human immunodeficiency virus (HIV) were evaluated by a second ELISA system (designated as ELISA-B) as well as by the Western blot technique. Both ELISA systems and the Western blot were positive in all of the 14 patients with clinical diagnoses of AIDS and AIDS-related persistent generalized lymphadenopathy (PGL). Of the 7 asymptomatic gays whose sera were repeatedly reactive in ELISA-A, 5 were also reactive in ELISA-B and these were the ones with positive Western blot tests. Eight and 17 ELISA-A reactive individuals were uncovered during a survey of 2,699 female prostitutes and 15,210 potential workers for Saudi Arabia respectively. All of these 25 individuals were ELISA-B and Western blot negative, an indication of false-positive reactivity with ELISA-A. Our studies indicate that the prevalence of HIV infection among the general Thai population is still low, and that the specificity of two ELISA test kits for anti-HIV may differ considerably. We concluded that evaluation of test kits should include studies in tropical countries where ecological conditions, climate and background endemic disease patterns are different than in the countries producing the diagnostic systems. Such studies are needed to identify the most sensitive and specific kits for worldwide application. We did discover that concordant positivity of two different ELISA test kits served as a reliable and inexpensive confirmatory test for anti-HIV.

Prevalence of HTLV-III/LAV antibody in selected populations in Thailand.

Antibody to the human T-lymphotropic virus, type III/lymphadenopathy-associated virus (HTLV-III/LAV) by ELISA test was detected in one (1%) of 101 male homosexual prostitutes (confidence limit 95%:0.03-5.4%, in two (2%) of 100 thalassemia patients, and in none (C.L. 95%:0-3.6%) of 100 female prostitutes, 99 parenteral drug abusers, 100 male VD patients, 100 consecutive blood donors in serum collected from February through June 1985. Serum from the positive homosexual subject was strongly positive on repeated ELISA testing, and was also positive by Western Blot test. The two thalassemia patients, who were repeatedly weakly-positive by ELISA, were negative by Western Blot test and presumed to be false positive reactors. Prevalence of HTLV-III/LAV virus in sexually-active homosexuals in Thailand in 1985 appears to be similar to the 1% rate among homosexuals in San Francisco in 1978 at the start of the AIDS epidemic there.