title: Pregnancy as a risk factor for severe outcomes from influenza virus infection: A systematic review and meta-analysis of observational studies.
abstract: Pregnancy is considered to be an important risk factor for severe complications following influenza virus infection. As a consequence, WHO recommendations prioritize pregnant women over other risk groups for influenza vaccination. However, the risk associated with pregnancy has not been systematically quantified.
  
  
  
  Systematic review and meta-analysis of observational studies that reported on pregnancy as a risk factor for severe outcomes from influenza virus infection.
  
  
  
  MEDLINE, EMBASE, CINAHL, and CENTRAL up to April 2014.
  
  
  
  Studies reporting on outcomes in pregnant women with influenza in comparison to non-pregnant patients with influenza. Outcomes included community-acquired pneumonia, hospitalization, admission to intensive care units (ICU), ventilatory support, and death.
  
  
  
  Two reviewers conducted independent screening and data extraction. A random effects model was used to obtain risk estimates. Ecological studies were summarized descriptively.
  
  
  
  A total of 142 non-ecological and 10 ecological studies were included. The majority of studies (n=136, 95.8%) were conducted during the 2009 influenza A (pH1N1) pandemic. There was a higher risk for hospitalization in pregnant versus non-pregnant patients infected with influenza (odds ratio [OR] 2.44, 95% CI 1.22-4.87), but no significant difference in mortality (OR 1.04, 95% CI 0.81-1.33) or other outcomes. Ecologic studies confirmed the association between hospitalization risk and pregnancy and 4 of 7 studies reported higher mortality rates in pregnant women.
  
  
  
  No studies were identified in which follow-up began prior to contact with the healthcare system and lack of adjustment for confounding factors.
  
  
  
  We found that influenza during pregnancy resulted in a higher risk of hospital admission than influenza infection in non-pregnant individuals, but that the risk of mortality following influenza was similar in both pregnant and non-pregnant individuals.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, ON, Canada; Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada; Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada; Michael G. DeGroote Institute for Infectious Diseases Research, McMaster University, Hamilton, ON, Canada.
authors.forename: Dominik
authors.initials: D
authors.lastname: Mertz
authors.affiliation: Department of Family Medicine (Midwifery), McMaster University, Hamilton, ON, Canada.
authors.forename: Johanna
authors.initials: J
authors.lastname: Geraci
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada.
authors.forename: Judi
authors.initials: J
authors.lastname: Winkup
authors.affiliation: Agence de Médecine Preventive, Paris, France.
authors.forename: Bradford D
authors.initials: BD
authors.lastname: Gessner
authors.affiliation: Initiative for Vaccine Research, World Health Organization, Geneva, Switzerland.
authors.forename: Justin R
authors.initials: JR
authors.lastname: Ortiz
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada; Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada; Michael G. DeGroote Institute for Infectious Diseases Research, McMaster University, Hamilton, ON, Canada. Electronic address: loebm@mcmaster.ca.
authors.forename: Mark
authors.initials: M
authors.lastname: Loeb
mesh_terms: D003422:Critical Care / Q000706:statistics & numerical data*; D005260:Female; D006760:Hospitalization; D006801:Humans; D007251:Influenza, Human / Q000150:complications* / Q000401:mortality / Q000473:pathology*; D064887:Observational Studies as Topic; D018410:Pneumonia, Bacterial / Q000453:epidemiology*; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000473:pathology*; D012121:Respiration, Artificial / Q000706:statistics & numerical data*; D012307:Risk Factors; D016019:Survival Analysis; D016896:Treatment Outcome
keywords: Influenza; Pregnancy; Risk; Systematic review; Vaccination