Background: In the early years of the worldwide pandemic, there were no reported cases of acquired immunodeficiency syndrome in Lesotho, a small, mountainous country in South Africa. Since 1986, when the first case of acquired immunodeficiency syndrome was identified, reported diagnoses have risen precipitously. The initiation of the Lesotho Highlands Water Project has resulted in the influx of a migrant workforce of predominantly single males into a relatively isolated, mountainous area where human immunodeficiency virus (HIV) was previously unknown. Objective: To ascertain the HIV seroprevalence among a cohort of laborers at the Katse Dam construction site in Bokong, Lesotho. Methods: During the 5-week study period in late 1992, construction workers (age range, 15 to 59 years) who were first-time clinic users for any chief complaint were randomly selected for serological study. Surveillance complied with the Lesotho National AIDS Control Programme guidelines, which required unlinked, anonymous testing. Serum samples were screened by an enzyme-linked immunosorbent assay; the results were confirmed by the Western blot technique. Results: Unlinked, anonymous HIV testing of 486 persons revealed a seroprevalence of 5.3% (26/486; 95% confidence interval, 3.3% to 7.3%). These data contrasted with a 0.8% seroprevalence in a similar age group in nearby villages that surrounded the construction project. Conclusions: Lesotho, in the early phase of the HIV/ acquired immunodeficiency syndrome epidemic in Africa in the 1980s, was seemingly protected by its relative isolation. Grave concern is now warranted as the country is destined to experience a rapid rise in HIV seroprevalence. Increased surveillance, health education opportunities, and aggressive prevention activities at the Katse Dam construction site are imperative to arrest the spread of HIV from construction workers to nearby villagers. © 1995, American Medical Association. All rights reserved.

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HIV Seroprevalence Human immunodeficiency virus infection risk Population Surveillance immigration human Cohort Studies priority journal screening South Africa Occupations Adolescent male female serodiagnosis prevalence Article Support, Non-U.S. Gov't adult health education seroepidemiology Sex Distribution age distribution Transients and Migrants Enzyme-Linked Immunosorbent Assay Middle Age