title: Weight and prognosis for influenza A(H1N1)pdm09 infection during the pandemic period between 2009 and 2011: a systematic review of observational studies with meta-analysis.
abstract: BACKGROUND
  In 2009, a novel influenza A(H1N1)pdm09 virus was detected and caused influenza pandemic. It is important to identify the risk factors for severe outcomes. However, inconsistent results regarding the effect of obesity were reported in previous studies.
  
  
  METHODS
  We conducted a systematic review to assess the association between obesity and poor prognosis for laboratory-confirmed A(H1N1)pdm09 influenza. We searched three English databases and three Chinese databases for relevant studies from April 2009 to October 2015: PubMed, the Cochrane library, Embase, CNKI, CBM, and Wanfang. Two investigators independently identified eligible articles, assessed quality using NOS, and extracted data. We performed meta-analyses and meta-regressions to estimate the association between weight and poor prognosis for influenza A(H1N1)pdm09 infection, when data were available.
  
  
  RESULTS
  We identified 22 articles enrolling 25,189 laboratory confirmed patients. The pooled estimates indicated obesity significantly increased the risk of fatal and critical complications of influenza A(H1N1)pdm09 infection (for fatal, OR = 1.81, 95% CI: 1.23-2.65; for critical complications, OR = 1.67, 95% CI: 1.13-2.47). However, we found significant interaction between early antiviral treatment and obesity (β = -0.28). After adjustment for early antiviral treatment, relationship between obesity and poor outcomes disappeared (OR = 1.14, 95% CI: 0.94-1.39).
  
  
  CONCLUSIONS
  The results of the meta-analyses showed obesity significantly increased the risk of death, critical complications, and severe complications for influenza A(H1N1)pdm09 infection, especially among high-quality studies and in Asia region. Importantly, the result from our meta-regression indicated that the conclusion should be interpreted with caution, because early antiviral treatment might be a key confounding factor.
authors.affiliation: a Institute for Infectious Diseases and Endemic Diseases Control, Beijing Center for Disease Prevention and Control (CDC) , Beijing , P.R. China ;
authors.forename: Ying
authors.initials: Y
authors.lastname: Sun
authors.affiliation: a Institute for Infectious Diseases and Endemic Diseases Control, Beijing Center for Disease Prevention and Control (CDC) , Beijing , P.R. China ;
authors.forename: Quanyi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: b School of Basic Medical Science , Beijing University of Chinese Medicine , Beijing , P.R. China ;
authors.forename: Guoyan
authors.initials: G
authors.lastname: Yang
authors.affiliation: a Institute for Infectious Diseases and Endemic Diseases Control, Beijing Center for Disease Prevention and Control (CDC) , Beijing , P.R. China ;
authors.forename: Changying
authors.initials: C
authors.lastname: Lin
authors.affiliation: a Institute for Infectious Diseases and Endemic Diseases Control, Beijing Center for Disease Prevention and Control (CDC) , Beijing , P.R. China ;
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: a Institute for Infectious Diseases and Endemic Diseases Control, Beijing Center for Disease Prevention and Control (CDC) , Beijing , P.R. China ;|c School of Public Health , Capital Medical University , Beijing , P.R. China ;|d Beijing Research Center for Preventive Medicine , Beijing , P.R. China.
authors.forename: Peng
authors.initials: P
authors.lastname: Yang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001835:Body Weight; D002648:Child; D002675:Child, Preschool; D005260:Female; D014943:Global Health; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology / Q000821:virology*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications*; D058873:Pandemics; D011379:Prognosis; D018570:Risk Assessment; D016019:Survival Analysis; D055815:Young Adult
keywords: Influenza A(H1N1)pdm09; meta-analysis; obesity; systematic review