OBJECTIVE: To evaluate the long-term impact of successive interventions on rates 
of methicillin-resistant Staphylococcus aureus (MRSA) colonization or infection 
and MRSA bacteremia in an endemic hospital-wide situation.
DESIGN: Quasi-experimental, interrupted time-series analysis. The impact of the 
interventions was analyzed by use of segmented regression. Representative MRSA 
isolates were typed by use of pulsed-field gel electrophoresis.
SETTING: A 950-bed teaching hospital in Seville, Spain.
PATIENTS: All patients admitted to the hospital during the period from 1995 
through 2008.
METHODS: Three successive interventions were studied: (1) contact precautions, 
with no active surveillance for MRSA; (2) targeted active surveillance for MRSA 
in patients and healthcare workers in specific wards, prioritized according to 
clinical epidemiology data; and (3) targeted active surveillance for MRSA in 
patients admitted from other medical centers.
RESULTS: Neither the preintervention rate of MRSA colonization or infection 
(0.56 cases per 1,000 patient-days [95% confidence interval {CI}, 0.49-0.62 
cases per 1,000 patient-days]) nor the slope for the rate of MRSA colonization 
or infection changed significantly after the first intervention. The rate 
decreased significantly to 0.28 cases per 1,000 patient-days (95% CI, 0.17-0.40 
cases per 1,000 patient-days) after the second intervention and to 0.07 cases 
per 1,000 patient-days (95% CI, 0.06-0.08 cases per 1,000 patient-days) after 
the third intervention, and the rate remained at a similar level for 8 years. 
The MRSA bacteremia rate decreased by 80%, whereas the rate of bacteremia due to 
methicillin-susceptible S. aureus did not change. Eighty-three percent of the 
MRSA isolates identified were clonally related. All MRSA isolates obtained from 
healthcare workers were clonally related to those recovered from patients who 
were in their care.
CONCLUSION: Our data indicate that long-term control of endemic MRSA is feasible 
in tertiary care centers. The use of targeted active surveillance for MRSA in 
patients and healthcare workers in specific wards (identified by means of 
analysis of clinical epidemiology data) and the use of decolonization were key 
to the success of the program.