title: Chronological, geographical, and seasonal trends of human cases of avian influenza A (H5N1) in Vietnam, 2003-2014: a spatial analysis.
abstract: BACKGROUND
  Human cases of highly pathogenic avian influenza A (H5N1) virus infection continue to occur in Southeast Asia. The objective of this study was to identify when and where human H5N1 cases have occurred in Vietnam and how the situation has changed from the beginning of the H5N1 outbreaks in 2003 through 2014, to assist with implementing methods of targeted disease management.
  
  
  METHODS
  We assessed the disease clustering and seasonal variation of human H5N1 cases in Vietnam to evaluate the geographical and monthly timing trends. The clustering of H5N1 cases and associated mortality were examined over three time periods: the outbreak period (2003-2005), the post-outbreak (2006-2009), and the recent period (2010-2014) using the flexibly shaped space-time scan statistic. The most likely cases to co-cluster and the elevated risks for incidence and mortality were assessed via calculation of the relative risk (RR). The H5N1 case seasonal variation was analysed as the cyclic trend in incidence data using Roger's statistical test.
  
  
  RESULTS
  Between 2003 and 2005, H5N1 cases (RR: 2.15, p = 0.001) and mortality (RR: 2.49, p = 0.021) were significantly clustered in northern Vietnam. After 2010, H5N1 cases tended to occur on the border with Cambodia in the south, while H5N1 mortality clustered significantly in the Mekong delta area (RR: 6.62, p = 0.002). A significant seasonal variation was observed (p < 0.001), with a higher incidence of morbidity in December through April.
  
  
  CONCLUSIONS
  These findings indicate that clinical preparedness for H5N1 in Vietnam needs to be strengthened in southern Vietnam in December-April.
authors: Teikyo University, Graduate School of Public Health, 2-11-1 Kaga, Itabashi-ku, Tokyo, 173-8605, Japan. manabe@kklabo.gr.jp.|Department of Hygiene and Public Health, Teikyo University School of Medicine, Tokyo, Japan. manabe@kklabo.gr.jp.|Waseda University, 1-21-1 Nishi-Waseda, Shinjuku-ku, Tokyo, Japan. manabe@kklabo.gr.jp.|University of Tsukuba, Graduate School of Comprehensive Human Sciences, Ibaraki, Japan. manabe@kklabo.gr.jp.
authors: Toshie
authors: T
authors: Manabe
authors: Teikyo University, Graduate School of Public Health, 2-11-1 Kaga, Itabashi-ku, Tokyo, 173-8605, Japan. kazue@med.teikyo-u.ac.jp.
authors: Kazue
authors: K
authors: Yamaoka
authors: Teikyo University, Graduate School of Public Health, 2-11-1 Kaga, Itabashi-ku, Tokyo, 173-8605, Japan. tango@medstat.jp.|Center for Medical Statistics, Tokyo, Japan. tango@medstat.jp.
authors: Toshiro
authors: T
authors: Tango
authors: Bach Mai Hospital, Intensive Care Unit, 78 Giai Phong, Dong Da, Hanoi, Vietnam. drbinhicu@gmail.com.
authors: Nguyen Gia
authors: NG
authors: Binh
authors: Bach Mai Hospital, Intensive Care Unit, 78 Giai Phong, Dong Da, Hanoi, Vietnam. daoxuanco@gmail.com.
authors: Dao Xuan
authors: DX
authors: Co
authors: Bach Mai Hospital, Intensive Care Unit, 78 Giai Phong, Dong Da, Hanoi, Vietnam. drtuan2004@yahoo.com.
authors: Nguyen Dang
authors: ND
authors: Tuan
authors: National Center for Global Health and Medicine, Division of Pulmonary Medicine, Tokyo, Japan. izumis-tky@umin.ac.jp.
authors: Shinyu
authors: S
authors: Izumi
authors: National Center for Global Health and Medicine, Division of Pulmonary Medicine, Tokyo, Japan. jintakajj@gmail.com.
authors: Jin
authors: J
authors: Takasaki
authors: Department of Pulmonary Medicine, Bach Mai Hospital, 78 Giai Phong, Dong Da, Hanoi, Vietnam. ngoquychaubmh@gmail.com.
authors: Ngo Quy
authors: NQ
authors: Chau
authors: Waseda University, 1-21-1 Nishi-Waseda, Shinjuku-ku, Tokyo, Japan. kudo@kklabo.gr.jp.|Koto Hospital, 6-8-5 Ojima, Koto-ku, Tokyo, Japan. kudo@kklabo.gr.jp.
authors: Koichiro
authors: K
authors: Kudo
mesh_terms: D001210:Asia, Southeastern / Q000453:epidemiology; D002160:Cambodia / Q000453:epidemiology; D002980:Climate; D016000:Cluster Analysis; D004196:Disease Outbreaks; D005843:Geography; D006801:Humans; D015994:Incidence; D053124:Influenza A Virus, H5N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000401:mortality / Q000821:virology; D012621:Seasons; D016019:Survival Analysis; D013997:Time Factors; D014744:Vietnam / Q000453:epidemiology