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Introduction
Previous research focusing on migrant workers in Sub-Saharan Africa has shown high HIV-1 prevalence and incidence. 1-3 In Zambia, a sparsely populated country in Southern Africa with a general population HIV-1 prevalence of 14.3% (16.1% among women and 12.3% among men) in 2007, migrant workers play a critical role in meeting production demands for many commercial and agricultural industries. 4 It is important to understand the extent of HIV-1 infection and the associated risk factors among this high-risk population in order to understand the driving forces of the epidemic and to prevent further spread of HIV-1 among migrant workers and their sexual contacts.
Historically, male seasonal workers have migrated from rural Western Zambia to Southern Zambia to work at large sugar estates during the annual 9-month harvesting season. Rural Western Zambia has high rates of syphilis, 5 which is a correlate of HIV-1 infection among women attending Zambian antenatal clinics. 6 Multiple studies have also demonstrated a strong association between HIV-1 infection and concurrent herpes simplex virus type 2 (HSV-2) infection 7 ; ongoing research to understand the biological mechanism for this association has identified important physiological and immunological changes. 8-10 We present results from a prospective cohort study of HIV-1 prevalence and observed incidence and associated risk factors among male migrant and non-migrant farm workers at a large sugar estate in Southern Zambia.
Materials and methods
Study setting and participants
The sugar estate, located in a transitional rural-urban town along a main transportation corridor in Zambia, employs ~2000 permanent workers year-round and 4000 migrant and non-migrant seasonal workers for the 9-month cane harvesting season. Nearly all migrant seasonal employees are male. Farm workers were eligible to participate if they were male, aged 18 years or older, and a seasonal employee (~1900 workers). Permanent and female farm workers were not eligible to participate. Participants were asked if they had moved to work at the sugar estate during the 2006 season to establish their migratory status. Eligible migrant seasonal workers consisted primarily of cane cutters (~900) originally from rural and remote areas of Zambia. Cane cutters are provided with shared housing, daily meals and a higher salary than other farm workers because of their physically demanding work and long hours. Non-migrant workers consisted of...