title: Impact of Influenza on Outpatient Visits, Hospitalizations, and Deaths by Using a Time Series Poisson Generalized Additive Model.
abstract: BACKGROUND
  The disease burden associated with influenza in developing tropical and subtropical countries is poorly understood owing to the lack of a comprehensive disease surveillance system and information-exchange mechanisms. The impact of influenza on outpatient visits, hospital admissions, and deaths has not been fully demonstrated to date in south China.
  
  
  METHODS
  A time series Poisson generalized additive model was used to quantitatively assess influenza-like illness (ILI) and influenza disease burden by using influenza surveillance data in Zhuhai City from 2007 to 2009, combined with the outpatient, inpatient, and respiratory disease mortality data of the same period.
  
  
  RESULTS
  The influenza activity in Zhuhai City demonstrated a typical subtropical seasonal pattern; however, each influenza virus subtype showed a specific transmission variation. The weekly ILI case number and virus isolation rate had a very close positive correlation (r = 0.774, P < 0.0001). The impact of ILI and influenza on weekly outpatient visits was statistically significant (P < 0.05). We determined that 10.7% of outpatient visits were associated with ILI and 1.88% were associated with influenza. ILI also had a significant influence on the hospitalization rates (P < 0.05), but mainly in populations <25 years of age. No statistically significant effect of influenza on hospital admissions was found (P > 0.05). The impact of ILI on chronic obstructive pulmonary disease (COPD) was most significant (P < 0.05), with 33.1% of COPD-related deaths being attributable to ILI. The impact of influenza on the mortality rate requires further evaluation.
  
  
  CONCLUSIONS
  ILI is a feasible indicator of influenza activity. Both ILI and influenza have a large impact on outpatient visits. Although ILI affects the number of hospital admissions and deaths, we found no consistent influence of influenza, which requires further assessment.
authors.affiliation: Public Health Emergency management office, Center for Disease Control and Prevention of Guangdong Province, Guangzhou, China.
authors.forename: Ru-ning
authors.initials: RN
authors.lastname: Guo
authors.affiliation: Institute of Immunization Programs, Center for Disease Control and Prevention of Guangdong Province, Guangzhou, China.
authors.forename: Hui-zhen
authors.initials: HZ
authors.lastname: Zheng
authors.affiliation: Department of Biostatistics, School of Public Health, Southern Medical University, Guangzhou, China.
authors.forename: Chun-quan
authors.initials: CQ
authors.lastname: Ou
authors.affiliation: Zhuhai Municipal Center for Disease Control and Prevention, Zhuhai, China.
authors.forename: Li-qun
authors.initials: LQ
authors.lastname: Huang
authors.affiliation: Zhuhai Municipal Center for Disease Control and Prevention, Zhuhai, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhou
authors.affiliation: Institute of Pathogenic Microorganisms, Center for Disease Control and Prevention of Guangdong Province, Guangzhou, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Zhuhai Municipal Center for Disease Control and Prevention, Zhuhai, China.
authors.forename: Can-kun
authors.initials: CK
authors.lastname: Liang
authors.affiliation: Center for Disease Control and Prevention of Guangdong Province, Guangzhou, China.
authors.forename: Jin-yan
authors.initials: JY
authors.lastname: Lin
authors.affiliation: Institute of Infectious Disease Prevention and Control, Center for Disease Control and Prevention of Guangdong Province, Guangzhou, China.
authors.forename: Hao-jie
authors.initials: HJ
authors.lastname: Zhong
authors.affiliation: Center for Disease Control and Prevention of Guangdong Province, Guangzhou, China.
authors.forename: Tie
authors.initials: T
authors.lastname: Song
authors.affiliation: Center for Disease Control and prevention, Beijing, China.
authors.forename: Hui-ming
authors.initials: HM
authors.lastname: Luo
mesh_terms: D000368:Aged; D000553:Ambulatory Care / Q000706:statistics & numerical data; D002681:China / Q000453:epidemiology; D017281:Cost of Illness; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007251:Influenza, Human / Q000191:economics* / Q000453:epidemiology / Q000401:mortality / Q000821:virology; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D016012:Poisson Distribution; D012141:Respiratory Tract Infections / Q000191:economics