Measles exportation from Japan to the United States, 1994 to 2006.
BACKGROUND
Imported measles cases and outbreaks involving Japanese travelers have been reported from the United States and other countries. For the United States, Japan is the top country of origin. The aims of this study were to analyze measles exportation trends from Japan to the United States and to suggest recommendations for improving monitoring and control in both countries.


METHODS
Reviewing all exportation cases reported to the Centers for Disease Control and Prevention and sentinel measles activity data monitored by the Japanese Ministry of Health between January 1994 and December 2006 (observation period).


RESULTS
A total of 63 cases were reported (median = 4 cases per year). Cases ranged in age from 9 months to 53 years (median = 17 y). Peaks occurred at 13 to 26 years and 12 to 35 months. Six cases were US citizens and 57 Japanese. Ten cases were reported in July and August, followed by eight in February and March. Twenty-seven cases were reported from Hawaii, followed by 15 from California and 6 from New York. Seven cases developed the secondary spread. Three of the cases had previously received one dose of measles vaccine, compared to 35 who were never immunized (25 cases unknown). During the observation period, measles activity exceeded the warning level in 157 weeks, with measles exportation occurring the subsequent week for 30 of these weeks. In comparison, during the 521 weeks in which measles activity was below the warning level, exportation of measles the following week was observed for 21 of those weeks (OR = 5.62, 95% CI = 3.12-10.2, p < 0.001).


CONCLUSIONS
Trend of exported measles cases from Japan to the United States has corresponded with the measles activity trend in Japan. Most of the cases were unvaccinated. This international health problem should be solved by strong leadership of Japanese public health professionals.
Takahashi
Hiroshi
H
Overseas Travelers' Clinic, Nagano Prefectural Suzaka Hospital, Suzaka City, Nagano, Japan. takahashimd@suzakahp.jp
Saito
Hiroshi
H
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D002487:Centers for Disease Control and Prevention, U.S.; D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks / Q000517:prevention & control* / Q000706:statistics & numerical data*; D018562:Disease Transmission, Infectious / Q000517:prevention & control; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007564:Japan; D008297:Male; D008457:Measles / Q000453:epidemiology* / Q000635:transmission*; D008458:Measles Vaccine / Q000627:therapeutic use; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods; D011322:Primary Prevention / Q000706:statistics & numerical data; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D014195:Travel; D014481:United States / Q000453:epidemiology
D008458:Measles Vaccine