Previously known MRSA carriage on admission versus ICU-acquired MRSA infection. Shown are the numbers of patients with previously known MRSA carriage on admission (MRSA colonization pressure) and the numbers of patients with ICU-acquired MRSA infections (surgical and medical ICUs; Geneva University Hospitals; January 2003 through August 2005). (a) (upper panel) Medical ICU. The vertical line on the figure indicates the initiation of rapid on-admission screening in November 2003 (phase II). The dashed vertical line indicates the initiation of pre-emptive isolation for all patients in April 2004 (phase III). (b) (lower panel) Surgical ICU. The vertical line on the figure indicates the initiation of rapid MRSA screening on admission and extension of pre-emptive isolation in November 2003 (phase II). ICU, intensive care unit; MRSA, methicillin-resistant Staphylococcus aureus.