Latitudinal patterns of travel among returned travelers with influenza: results from the GeoSentinel Surveillance Network, 1997-2007.
BACKGROUND
Influenza is a common vaccine-preventable disease among international travelers, but few data exist to guide use of reciprocal hemisphere or out-of-season vaccines.


METHODS
We analyzed records of ill-returned travelers in the GeoSentinel Surveillance Network to determine latitudinal travel patterns in those who acquired influenza abroad.


RESULTS
Among 37,542 ill-returned travelers analyzed, 59 were diagnosed with influenza A and 11 with influenza B. Half of travelers from temperate regions to the tropics departed outside influenza season. Twelve travelers crossed hemispheres from one temperate region to another, five during influenza season. Ten of 12 travelers (83%) with influenza who crossed hemispheres were managed as inpatients. Proportionate morbidity estimates for influenza A acquisition were highest for travel to the East-Southeast Asian influenza circulation network with 6.13 (95% CI 4.5-8.2) cases per 1000 ill-returned travelers, a sevenfold increased proportionate morbidity compared to travel outside the network.


CONCLUSIONS
Alternate hemisphere and out-of-season influenza vaccine availability may benefit a small proportion of travelers. Proportionate morbidity estimates by region of travel can inform pre-travel consultation and emphasize the ease of acquisition of infections such as influenza during travel.
Tropical Disease Unit, UHN-Toronto General Hospital, Toronto, ON, M5G 2C4 Canada. andrea.boggild@utoronto.ca
Andrea K
AK
Boggild
Francesco
F
Castelli
Philippe
P
Gautret
Joseph
J
Torresi
Frank
F
von Sonnenburg
Elizabeth D
ED
Barnett
Christina A
CA
Greenaway
Poh-Lian
PL
Lim
Eli
E
Schwartz
Annelies
A
Wilder-Smith
Mary E
ME
Wilson
D014943:Global Health; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D018571:Sentinel Surveillance; D011795:Surveys and Questionnaires; D014195:Travel / Q000706:statistics & numerical data*