Background: HIV took off rapidly in Zimbabwe during the 1980s. Yet, between 1998 and 2003, as the economy faltered, HIV prevalence declined abruptly and without clear explanation.
Methods: We reviewed epidemiological, behavioural, and economic data over three decades to understand changes in economic conditions, migrant labour and sex work that may account for observed fluctuations in Zimbabwe's HIV epidemic. Potential biases related to changing epidemic paradigms and data sources were examined.
Results: Early studies describe rural poverty, male migrant labour and sex work as conditions facilitating HIV/sexually transmitted infection (STI) transmission. By the mid-1990s, as Zimbabwe's epidemic became more generalized, research focus shifted to general population household surveys. Yet, less than half as many men than women were found at home during surveys in the 1990s, increasing to 80% during the years of economic decline. Other studies suggest that male demand for sex work fell abruptly as migrant workers were laid off, picking up again when the economy rebounded after 2009. Numbers of clients reported by sex workers, and their STI rates, followed similar patterns reaching a nadir in the early 2000s. Studies from 2009 describe a return to more active sex work, linked to increasing client demand, as well as a revitalized programme reaching sex workers.
Conclusion: The importance of the downturn in migrant labour and resultant changes in sex work may be underestimated as drivers of Zimbabwe's rapid HIV incidence and prevalence declines. Household surveys underrepresent populations at the highest risk of HIV/STI acquisition and transmission, and these biases vary with changing economic conditions.