Evaluating the Probability of Previously Unknown Carriage of MRSA at Hospital Admission

• Published in: The American journal of medicine Vol. 119; no. 3; pp. 275.e15 - 275.e23
• Main Authors: Harbarth, Stephan, Sax, Hugo, Fankhauser-Rodriguez, Carolina, Schrenzel, Jacques, Agostinho, Americo, Pittet, Didier
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2006
• Subjects: Admission; Aged; Carrier State - diagnosis; Carrier State - epidemiology; Case-Control Studies; Cross Infection - epidemiology; Cross Infection - prevention & control; Female; Hospitalization; Humans; Infection control; Male; Methicillin Resistance; Methicillin-resistant Staphylococcus aureus; Prediction; Predictive Value of Tests; Prevalence; Probability; Risk Factors; Staphylococcal Infections - epidemiology; Staphylococcal Infections - transmission; Switzerland - epidemiology; Switzerland; Prevalence; Admission; Methicillin-resistant Staphylococcus aureus; Prediction; Infection control
• ISSN: 0002-9343; 1555-7162; 1555-7162
• DOI: 10.1016/j.amjmed.2005.04.042

We determined the prevalence and risk profile of patients with previously unknown carriage of methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission. 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. Overall, 399 of 12 072 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 (≤1), 19% (92/482) in patients with an intermediate score (2-4), and 46% (84/182) in patients with a high score (≥5). The risk score had good discrimination (c-statistic, 0.73) and showed excellent calibration ( P = .88). 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.