title: Risk factors for severe illness with 2009 pandemic influenza A (H1N1) virus infection in China.
abstract: BACKGROUND
  Data on risk factors for severe outcomes from 2009 pandemic influenza A (H1N1) virus infection are limited outside of developed countries.
  
  
  METHODS
  We reviewed medical charts to collect data from patients hospitalized with laboratory-confirmed 2009 H1N1 infection who were identified across China during the period from September 2009 through February 2010, and we analyzed potential risk factors associated with severe illness (defined as illness requiring intensive care unit admission or resulting in death).
  
  
  RESULTS
  Among 9966 case patients, the prevalence of chronic medical conditions (33% vs 14%), pregnancy (15% vs 7%), or obesity (19% vs 14%) was significantly higher in those patients with severe illness than it was in those with less severe disease. In multivariable analyses, among nonpregnant case patients aged ≥ 2 years, having a chronic medical condition significantly increased the risk of severe outcome among all age groups, and obesity was a risk factor among those <60 years of age. The risk of severe illness among pregnant case patients was significantly higher for those in the second and third trimesters. The risk of severe illness was increased when oseltamivir treatment was initiated ≥ 5 days after illness onset (odds ratio, 1.42; 95% confidence interval, 1.20-1.67). For persons <60 years of age, the prevalence of obesity among case patients with severe illness was significantly greater than it was among those without severe illness or among the general population.
  
  
  CONCLUSIONS
  Risk factors for severe 2009 H1N1 illness in China were similar to those observed in developed countries, but there was a lower prevalence of chronic medical conditions and a lower prevalence of obesity. Obesity was a risk factor among case patients < 60 years of age. Early initiation of oseltamivir treatment was most beneficial, and there was an increased risk of severe disease when treatment was started ≥ 5 days after illness onset.
authors.affiliation: Office for Disease Control and Emergency Response, National Institute forViral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Hongjie
authors.initials: H
authors.lastname: Yu
authors.forename: Zijian
authors.initials: Z
authors.lastname: Feng
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Uyeki
authors.forename: Qiaohong
authors.initials: Q
authors.lastname: Liao
authors.forename: Lei
authors.initials: L
authors.lastname: Zhou
authors.forename: Luzhao
authors.initials: L
authors.lastname: Feng
authors.forename: Min
authors.initials: M
authors.lastname: Ye
authors.forename: Nijuan
authors.initials: N
authors.lastname: Xiang
authors.forename: Yang
authors.initials: Y
authors.lastname: Huai
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yuan
authors.forename: Hui
authors.initials: H
authors.lastname: Jiang
authors.forename: Yingdong
authors.initials: Y
authors.lastname: Zheng
authors.forename: Paul
authors.initials: P
authors.lastname: Gargiullo
authors.forename: Zhibin
authors.initials: Z
authors.lastname: Peng
authors.forename: Yunxia
authors.initials: Y
authors.lastname: Feng
authors.forename: Jiandong
authors.initials: J
authors.lastname: Zheng
authors.forename: Cuiling
authors.initials: C
authors.lastname: Xu
authors.forename: Yanping
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
authors.forename: Zhancheng
authors.initials: Z
authors.lastname: Gao
authors.forename: Weizhong
authors.initials: W
authors.lastname: Yang
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000998:Antiviral Agents / Q000008:administration & dosage; D002648:Child; D002675:Child, Preschool; D002681:China; D002908:Chronic Disease; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification* / Q000472:pathogenicity*; D007251:Influenza, Human / Q000401:mortality* / Q000473:pathology* / Q000821:virology; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications; D053139:Oseltamivir / Q000008:administration & dosage; D011247:Pregnancy; D012307:Risk Factors; D055815:Young Adult
chemical_list: D000998:Antiviral Agents; D053139:Oseltamivir