Migration is often the route through which people seek a wider world. There are economic, demographic, cultural, and social transitions associated with various forms of migration which have implications for the speed and nature of an epidemiological transition in the area affected by migration. The act of migration obviously exposes migrants to a different spatial environment, which in itself may be potentially beneficial or harmful. For example, migration may involve movement out of a malarial zone (a positive) to a slum area in a peri-urban settlement where the risk of airborne disease caused by pathogenic microbial agents is substantially higher (a negative). Migration can also involve a shift in social environment which may lead to changes in people’s behaviors and norms; this in turn may be associated with changes in diets and lifestyles. Of particular importance are changes that lead to increases in various risk factors, such as a more sedentary lifestyle and increased levels of smoking, alcohol use, and consumption of salt, sugar, and unhealthy oils and fats. In many cases migrants also experience increased stress from the disruption associated with leaving home.
To explore the connection between migration and epidemiological transitions, Mark Collinson offered an analysis of data from 1997–2008 from the Agincourt (Republic of South Africa) Health and Demographic Surveillance System. Significant levels of migration were reported, especially temporary labor migration among men and, increasingly, among women, Collinson said, and the average age of migrants appeared to be getting younger. Three types of migrants were considered in the analysis: one-way immigrants, short-duration labor migrants, and long-duration labor migrants. Even though the data covered only a fairly short time period, it was possible to observe changes in the causes of death in the Agincourt surveillance system. Communicable disease mortality and migration were both concentrated in the 25–49 age group. The most important age-and sex-related associations between migration and cause of death were seen between (1) one-way migrants (both sexes) and communicable disease; (2) short-duration female labor migrants or long-duration male labor migrants and communicable diseases; and (3) short-duration female labor migrants or long-duration male labor migrants and noncommunicable diseases.
The discussion during this session highlighted several general findings from an analysis of data collected by the International Network for the Demographic Evaluation of Populations and Their Health (INDEPTH) for Eastern and Southern Africa. The first was that high levels of circulation have exposed migrants to higher risks of HIV than would otherwise be the case. Second, return migration was said to be associated with higher adult mortality compared to that of local residents. Extant data suggest that rural households and health systems have an elevated burden of disease. Furthermore, given the intensity of population movements to and from INDEPTH sites, it is important to take migration into account in the formation of policies and programs. It was noted that
attrition from INDEPTH study populations is not random, which implies that migration affects the results obtained from surveillance-site data. Analysts should therefore consider adjusting for selection bias due to immigration and emigration.
