Context: Concerns about rates of methicillin-resistant Staphylococcus aureus (MRSA) health care-associated infections have prompted calls for mandatory screening or reporting in efforts to reduce MRSA infections.

Objective: To examine trends in the incidence of MRSA central line-associated bloodstream infections (BSIs) in US intensive care units (ICUs).

Design, setting, and participants: Data reported by hospitals to the Centers for Disease Control and Prevention (CDC) from 1997-2007 were used to calculate pooled mean annual central line-associated BSI incidence rates for 7 types of adult and non-neonatal pediatric ICUs. Percent MRSA was defined as the proportion of S aureus central line-associated BSIs that were MRSA. We used regression modeling to estimate percent changes in central line-associated BSI metrics over the analysis period.

Main outcome measures: Incidence rate of central line-associated BSIs per 1000 central line days; percent MRSA among S. aureus central line-associated BSIs.

Results: Overall, 33,587 central line-associated BSIs were reported from 1684 ICUs representing 16,225,498 patient-days of surveillance; 2498 reported central line-associated BSIs (7.4%) were MRSA and 1590 (4.7%) were methicillin-susceptible S. aureus (MSSA). Of evaluated ICU types, surgical, nonteaching-affiliated medical-surgical, cardiothoracic, and coronary units experienced increases in MRSA central line-associated BSI incidence in the 1997-2001 period; however, medical, teaching-affiliated medical-surgical, and pediatric units experienced no significant changes. From 2001 through 2007, MRSA central line-associated BSI incidence declined significantly in all ICU types except in pediatric units, for which incidence rates remained static. Declines in MRSA central line-associated BSI incidence ranged from -51.5% (95% CI, -33.7% to -64.6%; P < .001) in nonteaching-affiliated medical-surgical ICUs (0.31 vs 0.15 per 1000 central line days) to -69.2% (95% CI, -57.9% to -77.7%; P < .001) in surgical ICUs (0.58 vs 0.18 per 1000 central line days). In all ICU types, MSSA central line-associated BSI incidence declined from 1997 through 2007, with changes in incidence ranging from -60.1% (95% CI, -41.2% to -73.1%; P < .001) in surgical ICUs (0.24 vs 0.10 per 1000 central line days) to -77.7% (95% CI, -68.2% to -84.4%; P < .001) in medical ICUs (0.40 vs 0.09 per 1000 central line days). Although the overall proportion of S. aureus central line-associated BSIs due to MRSA increased 25.8% (P = .02) in the 1997-2007 period, overall MRSA central line-associated BSI incidence decreased 49.6% (P < .001) over this period.

Conclusions: The incidence of MRSA central line-associated BSI has been decreasing in recent years in most ICU types reporting to the CDC. These trends are not apparent when only percent MRSA is monitored.