The researchers compared the frequency of serious MRSA infections in patients admitted to the 3 hospitals in the 3 years of the study. For 3 years, the researchers tried to identify each patient who became sick with a serious MRSA infection while in any of the 3 hospitals. During the first year, they did nothing to detect newly admitted patients who were colonized with MRSA. In the second year, they tested all patients admitted to only the intensive care units in the 3 hospitals to see whether they were colonized with MRSA. If a patient tested positive for MRSA, their doctors put them on contact precautions. In the third year, they tested everyone who was admitted to the 3 hospitals and placed anyone who tested positive on contact precautions.