Commuting to work, rather than long-distance travel, seems to be the prime driving force behind the regional spread of influenza, U.S. researchers report.
Dr. Cecile Viboud, from the Fogarty International Center at the National Institutes of Health in Bethesda, Md., and colleagues used data on influenza-related deaths to analyze the spread of influenza in the US over the last 30 years.
At household and city levels, pediatric cases of influenza largely account for disease spread, whereas at regional levels, workplace commuting is the major factor, they report in the online issue of the research journal Science.
Influenza seasons with higher death rates correlate with higher disease spread and more rapid spread compared with lower mortality seasons, Viboud's group found.
More populous states, such as California, follow the national flu epidemic patterns, whereas less populous states, like Wyoming, show more erratic patterns.
The findings also indicate that flu season starts more often in California than anywhere else.
The researchers believe their analysis could be useful in predicting and planning for future influenza epidemics, as well as other infectious diseases.