Fig. 1

Flow-chart of the patient populations. Patients not infected with influenza on admission to the hospital are shown in green. Patients with influenza (blue) may be either detected or undetected. Influenza may be transmitted from the infected patients to non-infected, mainly by close contact by sharing rooms (purple). Patients with a known exposure to influenza (grey) are recommended prophylactic antiviral treatment. Some of the exposed patients yet develop influenza and thereby transfer to the blue flow, others remain in the green flow. A small number of influenza patients may recover during hospitalization (transferring from the blue flow to the green), others remain in the blue flow and are discharged while still infectious