Major article
Decreasing incidence of Staphylococcus aureus bacteremia over 9 years: Greatest decline in community-associated methicillin-susceptible and hospital-acquired methicillin-resistant isolates

https://doi.org/10.1016/j.ajic.2012.03.038Get rights and content

Background

The impact of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) emergence on the epidemiology of S aureus bacteremia (SAB) is not well documented.

Methods

This was an observational study of adult (aged ≥18 years) inpatients with SAB in a single 808-bed teaching hospital during 2002-2003, 2005-2006, 2008-2009, and 2010 with period-stratified SAB rate, onset mode, patient characteristics, and outcome.

Results

We encountered a total of 1,098 cases over the entire study period. The rate decreased steadily over time (from 6.64/103 discharges in 2002-2003 to 6.49/103 in 2005-2006, 5.24/103 in 2008-2009, and 5.00/103 in 2010; P = .0001), with a greater decline in community-associated cases (0.99/103, 0.77/103, 0.58/103, and 0.40/103, respectively; P = .0005) compared with health care–associated cases (5.65/103, 5.72/103, 4.66/103, and 4.60/103, respectively; P = .005). The decline was principally in MSSA (3.11/103, 2.21/103, 2.24/103, and 1.75/103, respectively; P = .00006), including both community-associated (P = .0002) and health care–associated cases (P = .006). Although overall rate changes in MRSA were not significant (P = .09), hospital-onset MRSA decreased markedly (P < .00001), whereas CA-MRSA increased (P = .03). The all-cause 100-day mortality rate did not change significantly (25.6% for 2002-2003, 25.2% for 2005-2006, 28.1% for 2008-2009, and 32.2% for 2010; P = .10). Differences in MSSA/MRSA-associated mortality decreased (20.1% vs 30.6%, P = .03 for 2002-2003; 18.1% vs 28.9%, P = .05 for 2005-2006; 21.7% vs 32.9%, P = .05 for 2008-2009; and 29.3% vs 34.9, P = .5 for 2010).

Conclusions

SAB incidence is decreasing, with the greatest decline in community-associated MSSA and hospital-onset MRSA cases. Most health care–associated cases currently are community-onset. MRSA/MSSA-related mortality is comparable. These changes are likely related to the emergence of CA-MRSA and the inpatient-to-outpatient shift in health care.

Section snippets

Patients and methods

The study was conducted at St John Hospital and Medical Center, a 803-bed teaching hospital in the Detroit metropolitan area.

Results

During the 4 study periods, we encountered 1,145 cases with one or more positive blood cultures for S aureus. Forty-seven of these cases were disqualified, including 21 with previous SAB within 100 days and 26 with no clinical signs of bacteremia. The remaining 1,098 cases were included in the rate assessment. For outcome measures, we excluded 49 additional cases with polymicrobial bacteremia.

The rate of SAB decreased significantly over time (P = .0001). This decrease was related mainly to the

Discussion

Our data reveal new trends in SAB, with a steadily decreasing rate over time. This decrease was noted in community-associated and hospital-onset cases, whereas the rate of community-onset health care–associated cases did not change. Decreasing rates of MRSA central line–associated bacteremia and health care–associated invasive MRSA infections have been reported recently.4, 5 Our findings substantiate the decline in hospital-onset bacteremia, but also reveal a concomitant decline in

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Supported by the St John Hospital Medical Education Fund.

Conflict of interest: None to report.

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