Pandemic 2009 H1N1 influenza among health care workers.

To evaluate factors associated with pandemic influenza among health care workers (HCWs), a case-case-control study was conducted with 52 confirmed cases, 120 influenza-negative cases, and 102 controls. Comorbidities (odds ratio [OR], 19.05; 95% confidence interval [95% CI]: 4.75-76.41), male sex (OR, 5.11; 95% CI: 1.80-14.46), and being a physician (OR, 8.58; 95% CI: 2.52-29.27) were independent risk factors for pandemic influenza infection among HCWs. Contact with symptomatic coworker or social contact was protective (OR, 0.11; 95% CI: 0.04-0.29). To our knowledge, this is the first study of factors associated with acquiring influenza involving HCW in nonsevere cases.