title: Impact of influenza exposure on rates of hospital admissions and physician visits because of respiratory illness among pregnant women.
abstract: BACKGROUND
  Excess deaths have occurred among pregnant women during influenza pandemics, but the impact of influenza during nonpandemic years is unclear. We evaluated the impact of exposure during nonpandemic influenza seasons on the rates of hospital admissions and physician visits because of respiratory illness among pregnant women.
  
  
  METHODS
  We conducted a 13-year (1990-2002) population-based cohort study involving pregnant women in Nova Scotia. We compared rates of hospital admissions and physician office visits because of respiratory illness during the influenza season in each trimester of pregnancy with rates during the influenza season in the year before pregnancy and with rates in non-influenza seasons. Poisson regression analyses were performed to estimate rate ratios and 95% confidence intervals (CIs).
  
  
  RESULTS
  Of 134,188 pregnant women in the study cohort, 510 (0.4%) were admitted to hospital because of a respiratory illness during pregnancy and 33,775 (25.2%) visited their physician for the same reason during pregnancy. During the influenza seasons, the rate ratio of hospital admissions in the third trimester compared with admissions in the year before pregnancy was 7.9 (95% CI 5.0-12.5) among women with comorbidities and 5.1 (95% CI 3.6-7.3) among those without comorbidities. The rate of hospital admissions in the third trimester among women without comorbidities was 7.4 per 10,000 woman-months during the influenza season, compared with 5.4 and 3.1 per 10,000 woman-months during the peri-and non-influenza seasons respectively. Corresponding rates among women with comorbidities were 44.9, 9.3 and 18.9 per 10,000 woman-months. Only 6.7% of women with comorbidities had received influenza immunization.
  
  
  CONCLUSIONS
  Our data support the recommendation that pregnant women with comorbidities should receive influenza vaccination regardless of their stage of pregnancy during the influenza season. Since hospital admissions because of respiratory illness during the influenza season were also increased among pregnant women without comorbidities, all pregnant women are likely to benefit from influenza vaccination.
authors.affiliation: Canadian Centre for Vaccinology, Halifax, NS. l.dodds@dal.ca
authors.forename: Linda
authors.initials: L
authors.lastname: Dodds
authors.forename: Shelly A
authors.initials: SA
authors.lastname: McNeil
authors.forename: Deshayne B
authors.initials: DB
authors.lastname: Fell
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Allen
authors.forename: Ann
authors.initials: A
authors.lastname: Coombs
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Scott
authors.forename: Noni
authors.initials: N
authors.lastname: MacDonald
mesh_terms: D000328:Adult; D015331:Cohort Studies; D015897:Comorbidity; D016001:Confidence Intervals; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D007252:Influenza Vaccines / Q000008:administration & dosage; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D009674:Nova Scotia / Q000453:epidemiology; D009819:Office Visits / Q000706:statistics & numerical data*; D016012:Poisson Distribution; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000175:diagnosis / Q000453:epidemiology*; D011256:Pregnancy Outcome; D011264:Pregnancy Trimesters; D012016:Reference Values; D012140:Respiratory Tract Diseases / Q000453:epidemiology* / Q000517:prevention & control; D012189:Retrospective Studies; D018570:Risk Assessment; D014611:Vaccination / Q000592:standards
chemical_list: D007252:Influenza Vaccines