The plan was thus modifi ed. An initial serum sample was obtained from all participants to measure for pandemic infl uenza antibodies. At study entry, participants completed a Web-or paper-based questionnaire that requested information on demographic characteristics, known infl uenza exposures outside the workplace, and any history of fever or respiratory symptoms occurring during the pandemic but before the study. In addition, the clinical group was asked about work exposure to patients with suspected pandemic infl uenza and their usual use of PPE when caring for these patients. Participants were also asked about use of neuraminidase inhibitors (NIs) and specifi cally whether they received prophylaxis after exposure to a patient with confi rmed infl uenza.