Global travel patterns and risk of measles in Ontario and Quebec, Canada: 2007-2011.
BACKGROUND
In 2011 the largest measles outbreak in North America in a decade occurred in Quebec, Canada with over 700 cases. In contrast, measles activity in neighbouring province Ontario remained low (8 cases). Our objective was to determine the extent to which the difference could be explained by differing travel patterns.


METHODS
We explored the relationship between measles cases over 2007-2011, by importation classification, in Quebec and Ontario in relation to global travel patterns to each province using an ecological approach. Global measles exposure was estimated by multiplying the monthly traveler volume for each country of origin into Quebec or Ontario by the yearly measles incidence rate for the corresponding country. Visual inspection of temporal figures and calculation of Pearson correlation coefficients were performed.


RESULTS
Global measles exposure was similar in Ontario and Quebec. In Quebec, there was a nearly perfectly linear relationship between annual measles cases and its global measles exposure index over 2007-2011 (r = 0.99, p = 0.001). In contrast, there was a non-significant association in Ontario. The 2011 rise in Quebec's index was largely driven by a dramatic increase in measles activity in France the same year.


CONCLUSIONS
Global measles activity was associated with measles epidemiology in Quebec. Global measles exposure risk is higher in Ontario than Quebec. Differences in measles epidemiology between Ontario and Quebec from 2007-2011 are not explained by greater exposure in Quebec. A combination of alternative factors may be responsible, including differences in population susceptibility.
Public Health Ontario, Toronto, ON, Canada. sarah.wilson@oahpp.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. sarah.wilson@oahpp.ca.
Sarah E
SE
Wilson
St Michael's Hospital, Department of Medicine, Division of Infectious Diseases, Toronto, ON, Canada. khank@smh.ca.|Centre for Research on Inner City Health, Keenan Research Centre, Li Ka Shing Knowledge Institute, Toronto, ON, Canada. khank@smh.ca.|Faculty of Medicine, Division of Infectious Diseases, University of Toronto, Toronto, ON, Canada. khank@smh.ca.
Kamran
K
Khan
Institut national de santé publique du Québec, Québec, QC, Canada. vladimir.Gilca@inspq.qc.ca.|Université Laval, Laval, QC, Canada. vladimir.Gilca@inspq.qc.ca.
Vladimir
V
Gilca
Centre for Research on Inner City Health, Keenan Research Centre, Li Ka Shing Knowledge Institute, Toronto, ON, Canada. MiniotaJ@smh.ca.
Jennifer
J
Miniota
Public Health Ontario, Toronto, ON, Canada. shelley.deeks@oahpp.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. shelley.deeks@oahpp.ca.
Shelley L
SL
Deeks
Public Health Ontario, Toronto, ON, Canada. gillian.lim@oahpp.ca.
Gillian
G
Lim
Centre for Research on Inner City Health, Keenan Research Centre, Li Ka Shing Knowledge Institute, Toronto, ON, Canada. rose.eckhardt@gmail.com.
Rose
R
Eckhardt
Public Health Ontario, Toronto, ON, Canada. shelly.bolotin@oahpp.ca.
Shelly
S
Bolotin
Public Health Ontario, Toronto, ON, Canada. natasha.crowcroft@oahpp.ca.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada. natasha.crowcroft@oahpp.ca.|Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada. natasha.crowcroft@oahpp.ca.
Natasha S
NS
Crowcroft
D004196:Disease Outbreaks; D004198:Disease Susceptibility; D006801:Humans; D008457:Measles / Q000453:epidemiology* / Q000517:prevention & control; D008458:Measles Vaccine / Q000627:therapeutic use; D009864:Ontario / Q000453:epidemiology; D011792:Quebec / Q000453:epidemiology; D012307:Risk Factors; D012621:Seasons; D014195:Travel
D008458:Measles Vaccine