Epidemiology and Infection

Original Papers

Influenza and respiratory tract infections

Effect of environmental factors on the spatio-temporal patterns of influenza spread

K. M. L. CHARLANDa1a2a3a4 c1, D. L. BUCKERIDGEa2, J. L. STURTEVANTa1a5, F. MELTONa6a7, B. Y. REISa1a3a4, K. D. MANDLa1a3a4 and J. S. BROWNSTEINa1a3a4

a1 Children's Hospital Informatics Program at the Harvard-MIT Division of Health Sciences and Technology, Boston, MA, USA

a2 McGill Clinical and Health Informatics (MCHI), McGill University, Montreal, Quebec, Canada

a3 Division of Emergency Medicine, Children's Hospital Boston, Boston, MA, USA

a4 Department of Pediatrics, Harvard Medical School, Boston, MA, USA

a5 Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA

a6 California State University, at Monterey Bay, Seaside, CA, USA

a7 NASA Ames Research Center, Moffett Field, CA, USA


Although spatio-temporal patterns of influenza spread often suggest that environmental factors play a role, their effect on the geographical variation in the timing of annual epidemics has not been assessed. We examined the effect of solar radiation, dew point, temperature and geographical position on the city-specific timing of epidemics in the USA. Using paediatric in-patient data from hospitals in 35 cities for each influenza season in the study period 2000–2005, we determined ‘epidemic timing’ by identifying the week of peak influenza activity. For each city we calculated averages of daily climate measurements for 1 October to 31 December. Bayesian hierarchical models were used to assess the strength of association between each variable and epidemic timing. Of the climate variables only solar radiation was significantly related to epidemic timing (95% CI −0·027 to −0·0032). Future studies may elucidate biological mechanisms intrinsically linked to solar radiation that contribute to epidemic timing in temperate regions.

(Accepted February 02 2009)

(Online publication March 19 2009)


c1 Author for correspondence: Dr K. M. L. Charland, 1 Autumn Street, Room 439, Boston, MA 02215, USA. (Email: Katia.Charland@childrens.harvard.edu)