The transmission of influenza during the years in which H1N1 was circulating was amplified by concentrated swine feeding operations, a recent study found. The spatiotemporal association between influenza-like illnesses (ILIs) and licensed swine operations from 2008 to 2012 in North Carolina was investigated. Researchers found:

• ILI peaked earlier in counties with a higher number of licensed swine operations during the 2009-2010 and 2010-2011 influenza seasons, both seasons in which the pandemic 2009 H1N1 influenza A virus circulated.
• This trend was not observed in 2008-2009 or 2011-2012; nor was any relationship between ILI onset week and number of swine operations.

The authors concluded that the study results have implications for vaccine strategies targeting swine workers, as well as virologic surveillance in areas with large concentrations of swine.