Methicillin-resistant Staphylococcus aureus colonization is a predictive factor for the resistance pattern of an infectious strain of S-aureus.

Objective: To assess the predictive value of a previous colonization with m ethicillin-resistant Staphylococcus aureus for the resistance pattern of a bacteriological specimen significantly positive to S. aureus. Study design: Retrospective study of patients' files. Patients: Patients admitted for at least 48 hours in a surgical intensive c are unit from April 1, 1996 to December 31, 1997. Methods: Collection of patients' characteristics and chronology of positive microbiological specimens with methicillin-susceptible (MSSA) or -resistan t (MRSA) S. aureus from medical and laboratory records. During the study pe riod, screening for nasal or perineal colonization with MRSA was systematic ally performed on admission and weekly thereafter. Results: The files of 540 patients were reviewed. MRSA and MSSA infections occurred in 7% (39/540) and 4% (20/ 540) of the patients respectively. By o pposition with MSSA infections, MRSA infections occurred more frequently in patients previously colonized with MRSA (13 infections in 63 colonized pat ients [21%] versus 7 infections in 477 noncolonized patients [2%], odds rat io = 18, confidence interval : 6-51, P < 0.0001). The median delay between colonization and infection was 5 days. The positive and negative predictive values for previous colonization with MRSA to predict infection with MRSA in presence of a bacteriological specimen significantly positive with S. au reus were 81 and 84%. respectively. Conclusion: The probabilistic use of a glycopeptide in presence of a bacter iological specimen significantly positive with S. aureus should be limited to patients already colonized with MRSA. in order to decrease the abusive a dministration of these antibiotics. (C) 2000 Editions scientifiques ei medi cales Elsevier SAS.