Using Geospatial Tools to Identify Priority Worker Populations for Virologic Surveillance and Prevention of Emerging Influenza Pandemics

BACKGROUND: Pigs have receptors for both avian and human influenza viruses and may, therefore, serve as mixing vessels from which new viruses may emerge and be transmitted to humans. Settings where swine, poultry and humans coexist in close contact increase opportunities for such interspecies transmission and viral reassortment to occur. The consolidation and geographic concentration of food animal production in the US raises concerns that increasing numbers of swine operations in close proximity to poultry facilities could contribute to the occurrence of future influenza pandemics. The increased risk of farmers, farmworkers and others in close contact with industrial food animal production to be infected with viruses from food animals has been well documented. Such workers comprise a potentially important sentinel population in which human infections with new, reassortant influenza viruses may be more likely to be detected early. Identification and characterization of these priority workers in the US is useful for the purpose of both virologic surveillance and targeting prevention efforts.

METHODS: We use data from the Homeland Security Infrastructure Program (HSIP) dataset to describe the spatial distribution of swine and poultry operations in the United States and explore the intersection of high-density swine and poultry operation areas. Using spatial analysis tools available in ArcGIS 10, we identify swine operations where workers may be at high risk for exposure to new reassortant influenza viruses based on their proximity (within 5 km) to poultry facilities. We also identify counties with high densities of such facilities and estimate the population size of workers employed at them.

RESULTS:  Maps displaying the spatial distributions of swine and poultry operations and their intersection are presented. We identified a single cluster of 5 contiguous counties in eastern North with high densities of swine operations that were within 5 km of a poultry facility. The total number of workers employed at these operations in the 5 cluster counties ranged from 42 to 1,271.

CONCLUSIONS:  Swine farmers and farmworkers in eastern North Carolina comprise a potentially important sentinel population for the emergence of novel influenza viruses. This worker population should be considered for enhanced virologic surveillance and prevention efforts. Geospatial analysis of HSIP data is a useful tool for occupational health surveillance and emergency preparedness. Identification of priority worker populations that may be at increased risk for chemical or biological exposure and the jurisdictions where they work has applications for the implementation of both surveillance and prevention efforts.