Evaluating the probability of previously unknown carriage of MRSA at hospital admission.
OBJECTIVE
We determined the prevalence and risk profile of patients with previously unknown carriage of methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission.


METHODS
We conducted a 7-month, prospective case-controlled study in adult inpatients admitted to a university hospital with endemic MRSA. Multivariate conditional logistic regression for data sets matched 1:4 was performed to identify the risk profile of newly identified MRSA carriers.


RESULTS
Overall, 399 of 12072 screened admissions (prevalence, 3.3%) were found colonized (n = 368, 92%) or infected (n = 31, 8%) with MRSA. In 204 cases (prevalence, 1.7%), MRSA carriage was newly identified. Without screening on admission, 49% (196/399) of MRSA carriers would have been missed. We identified nine independent risk factors for newly identified MRSA carriage at admission (adjusted odds ratio): male sex (1.9); age greater than 75 years (2.0); receipt of fluoroquinolones (2.7), cephalosporins (2.1), and carbapenems (3.2) in the last 6 months; previous hospitalization (1.9) or intravenous therapy (1.7) during the last 12 months; urinary catheter at admission (2.0); and intrahospital transfer (2.4). A risk score (range, 0-13) was calculated by adding points assigned to these variables. On the basis of analysis of 1006 patients included in the case-controlled study, the probability of MRSA carriage was 8% (28/342) in patients with a low score (< or =1), 19% (92/482) in patients with an intermediate score (2-4), and 46% (84/182) in patients with a high score (> or =5). The risk score had good discrimination (c-statistic, 0.73) and showed excellent calibration (P = .88).


CONCLUSIONS
On-admission prevalence of previously unknown MRSA carriers was high. Applying the risk score to newly admitted patients with an intermediate or high probability of MRSA carriage could allow a more effective MRSA control strategy.
Infection Control Program and Division of Infectious Diseases, University of Geneva Hospitals, Geneva, Switzerland. stephan.harbarth@hcuge.ch
Stephan
S
Harbarth
Hugo
H
Sax
Carolina
C
Fankhauser-Rodriguez
Jacques
J
Schrenzel
Americo
A
Agostinho
Didier
D
Pittet
D000368:Aged; D002353:Carrier State / Q000175:diagnosis* / Q000453:epidemiology; D016022:Case-Control Studies; D003428:Cross Infection / Q000453:epidemiology / Q000517:prevention & control*; D005260:Female; D006760:Hospitalization; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D011237:Predictive Value of Tests; D015995:Prevalence; D011336:Probability; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000635:transmission; D013557:Switzerland / Q000453:epidemiology