Outcome and attributable mortality in critically Ill patients with bacteremia involving methicillin-susceptible and methicillin-resistant Staphylococcus aureus.
BACKGROUND
Staphylococcus aureus bacteremia carries high mortality rates. The clinical impact of methicillin resistance remains controversial: outcome comparisons between patients with bacteremia involving methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) S aureus are difficult to perform because of important differences in severity of illness.


METHODS
A retrospective cohort analysis and 2 independent case-control analyses were performed to determine and compare outcomes and attributable mortality rates of MSSA (n = 38) and MRSA bacteremia (n = 47) in critically ill patients. For the case-control studies, matching (1:2 ratio) was based on the APACHE (Acute Physiology and Chronic Health Evaluation) II classification: APACHE II score (+/-1 point) and diagnostic category.


RESULTS
Patients with MRSA bacteremia had more acute renal failure and hemodynamic instability than patients with MSSA bacteremia. They had a longer intensive care unit stay and ventilator dependency. Patients with MRSA bacteremia had a higher 30-day mortality rate (53.2% vs 18.4%) and in-hospital mortality rate (63.8% vs 23.7%) (P<.05). Multivariate survival analysis demonstrated acute renal failure, length of mechanical ventilation, age, and methicillin resistance to be independently associated with mortality (P<.05). The attributable mortality rate for MSSA bacteremia was 1.3%: mortality rates for cases and controls were respectively 23.7% and 22.4% (P =.94). The attributable mortality rate for MRSA bacteremia was 23.4%: mortality rates for cases and controls were respectively 63.8% and 40.4% (P =.02). The difference (22.1%) between both attributable mortality rates was significant (95% confidence interval, 8.8%-35.3%).


CONCLUSIONS
In critically ill patients, after accurate adjustment for disease severity and acute illness, we found MRSA bacteremia to have a higher attributable mortality than MSSA bacteremia.
Blot
Stijn I
SI
Ghent University Hospital, Department of Intensive Care, De Pintelaan 185, B-9000 Ghent, Belgium. Stijn.Blot@rug.ac.be
Vandewoude
Koenraad H
KH
Hoste
Eric A
EA
Colardyn
Francis A
FA
D058186:Acute Kidney Injury / Q000150:complications; D000368:Aged; D016470:Bacteremia / Q000150:complications / Q000382:microbiology* / Q000401:mortality; D016022:Case-Control Studies; D015331:Cohort Studies; D003428:Cross Infection / Q000150:complications / Q000382:microbiology* / Q000401:mortality; D006801:Humans; D007902:Length of Stay; D016106:Methicillin Resistance; D008875:Middle Aged; D015999:Multivariate Analysis; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000150:complications / Q000382:microbiology* / Q000401:mortality; D013211:Staphylococcus aureus / Q000187:drug effects*; D015996:Survival Rate