title: Influenza vaccination of healthcare workers in acute-care hospitals: a case-control study of its effect on hospital-acquired influenza among patients.
abstract: BACKGROUND
  In acute-care hospitals, no evidence of a protective effect of healthcare worker (HCW) vaccination on hospital-acquired influenza (HAI) in patients has been documented. Our study objective was to ascertain the effectiveness of influenza vaccination of HCW on HAI among patients.
  
  
  METHODS
  A nested case-control investigation was implemented in a prospective surveillance study of influenza-like illness (ILI) in a tertiary acute-care university hospital. Cases were patients with virologically-confirmed influenza occurring ≥ 72 h after admission, and controls were patients with ILI presenting during hospitalisation with negative influenza results after nasal swab testing. Four controls per case, matched per influenza season (2004-05, 2005-06 and 2006-07), were randomly selected. Univariate and multivariate conditional logistic regression models were fitted to assess factors associated with HAI among patients.
  
  
  RESULTS
  In total, among 55 patients analysed, 11 (20%) had laboratory-confirmed HAI. The median HCW vaccination rate in the units was 36%. The median proportion of vaccinated HCW in these units was 11.5% for cases vs. 36.1% for the controls (P = 0.11); 2 (20%) cases and 21 (48%) controls were vaccinated against influenza in the current season (P = 0.16). The proportion of ≥ 35% vaccinated HCW in short-stay units appeared to protect against HAI among patients (odds ratio = 0.07; 95% confidence interval 0.005-0.98), independently of patient age, influenza season and potential influenza source in the units.
  
  
  CONCLUSIONS
  Our observational study indicates a shielding effect of more than 35% of vaccinated HCW on HAI among patients in acute-care units. Investigations, such as controlled clinical trials, are needed to validate the benefits of HCW vaccination on HAI incidence in patients.
authors.affiliation: Hospices Civils de Lyon, Hôpital Edouard Herriot, Service d'Hygiène, Epidémiologie et Prévention, Lyon, France. thomas.benet@chu-lyon.fr
authors.forename: Thomas
authors.initials: T
authors.lastname: Bénet
authors.forename: Corinne
authors.initials: C
authors.lastname: Régis
authors.forename: Nicolas
authors.initials: N
authors.lastname: Voirin
authors.forename: Olivier
authors.initials: O
authors.lastname: Robert
authors.forename: Bruno
authors.initials: B
authors.lastname: Lina
authors.forename: Silene
authors.initials: S
authors.lastname: Cronenberger
authors.forename: Brigitte
authors.initials: B
authors.lastname: Comte
authors.forename: Brigitte
authors.initials: B
authors.lastname: Coppéré
authors.forename: Philippe
authors.initials: P
authors.lastname: Vanhems
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D003428:Cross Infection / Q000453:epidemiology / Q000517:prevention & control*; D005260:Female; D006282:Health Personnel; D006385:Hemagglutination Inhibition Tests; D006761:Hospitals; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D009666:Nose / Q000821:virology; D009975:Orthomyxoviridae / Q000302:isolation & purification; D011446:Prospective Studies; D014611:Vaccination / Q000706:statistics & numerical data*
chemical_list: D007252:Influenza Vaccines