LETTERS Influenza (H1N1) 2009 virus was spreading widely to each school’s administrator. The pre- other schools and communities and fecture-wide school closure strategy 2009 Outbreak and that school closures would be neces- may have had an effect on not only the School Closure, sary (1,2). reduction of virus transmission and Osaka Prefecture, The governor of Osaka decided elimination of successive large out- to close all 270 high schools and 526 breaks but also greater public aware- Japan junior high schools in Osaka Prefec- ness about the need for preventive To the Editor: The Osaka Prefec- ture from Monday, May 18, to Sunday, measures. tural Government, the third largest lo- May 24, following the weekend days cal authority in Japan and comprising of May 16 and 17 observed at most Acknowledgments 43 cities (total population 8.8 million), schools. Students were ordered to stay We thank the public health centers in was informed of a novel influenza out- at home (3). Most nurseries, primary Osaka, Sakai, Higashiosaka, and Takatsuki break on May 16, 2009. A high school schools, colleges, and universities for data collection and the National Insti- submitted an urgent report that ≈100 in the 9 cities with influenza cases tute of Infectious Disease, Tokyo, for help- students had influenza symptoms; voluntarily followed the governor’s ful advice. an independent report indicated that decision. Antiviral drugs were pre- scribed by local physicians to almost a primary school child also showed Ryosuke Kawaguchi, all students with confirmed infection; similar symptoms. Masaya Miyazono, families were given these drugs as a The Infection Control Law in Ja- Tetsuro Noda, prophylactic measure. Family mem- pan requires that all novel influenza Yoshihiro Takayama, bers of an infected student were also cases diagnosed by physicians and Yasunori Sasai, strongly encouraged to stay home at confirmed by laboratory test results and Hiroyasu Iso least 7 days after the student’s symp- be reported to public health centers. Author affiliations: Osaka Prefectural Gov- toms had disappeared. Most newspa- Influenza A pandemic (H1N1) 2009 ernment, Osaka, Japan (R. Kawaguchi, M. pers and radio and television stations infection was first detected in 2 stu- Miyazono, T. Noda, Y. Takayama, Y. Sasai); began reporting the outbreak on May dents in the same high school on May and Osaka University Graduate School of 16, and a national campaign emerged 11, 2009, followed by an outbreak in Medicine and Public Health, Osaka (H. Iso) a high school in city A in northern in which facemask use was recom- Osaka Prefecture (online Appendix mended to the public along with good DOI: 10.3201/eid1510.091029 Table, available from http://www.cdc. hygiene practices such as hand wash- gov/EID/content/15/10/1685-appT. ing and gargling. References After the school closures, the htm). Two days later on May 13 in 1. Markel H, Lipman HB, Navarro JA, Sloan city B in middle Osaka Prefecture, a number of newly reported cases de- A, Michalsen JR, Stern AM, et al. Non- primary school student and a junior clined rapidly from 30 cases on May pharmaceutical interventions implemented high school student were found to be 17 to none by May 25. During that by US cities during the 1918–1919 influ- time, 13 schools reported only 1 new enza pandemic. JAMA. 2007;298:644–54. infected. Infections were also detected DOI: 10.1001/jama.298.6.644 among school children in 6 other cit- case each. After May 25, although no 2. Glass LM, Glass RJ. Social contact net- ies on May 14; six parents of students new cases were found among students, works for the spread of pandemic influen- from the first outbreak school were some sporadic cases were identified za in children and teenagers. BMC Public among adults by the end of May. From Health 2008;8:ARTN61. also infected. 3. Johnson AJ, Moore ZS, Edelson PJ, Kin- We obtained anecdotal infor- June 1 through June 22, twenty-five nane L, Davies M, Shay DK, et al. House- mation that influenza seemed to be sporadic cases (of which 19 had be- hold responses to school closure resulting transmitted from infected students in come infected overseas) were report- from outbreak of influenza B. Emerg In- ed, but no further outbreaks were re- fect Dis. 2008;14:1024–30. DOI: 10.3201/ the first high school outbreak to stu- eid1407.080096 dents in other schools either because ported in the schools. Since June 23, smaller school students had siblings who attended Address for correspondence: Ryosuke outbreaks have occurred in cities in other schools or students were part Kawaguchi, Osaka Prefectural Government, southern Osaka Prefecture. The gov- of the same extracurricular clubs and Department of Health and Medical Care 2-1-22, ernment decided not to conduct the cram schools (lessons after school to Otemae, Chuo-ku, Osaka City, Japan; email: prefecture-wide school closure for supplement schoolwork managed by [email protected] a private company). Therefore, we these outbreaks. Instead, the decision concluded that the influenza (H1N1) regarding school closure was left to Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 15, No. 10, October 2009 1685 .