Is methicillin-resistant Staphylococcus aureus more contagious than methicillin-susceptible S. aureus in a surgical intensive care unit?

Abstract

Background and objective: In the Netherlands, the prevalence of methicillin resistance among Staphylococcus aureus isolates has been kept to less than 1% by using active screening programs and isolation. At the University Medical Center Utrecht (UMCU), an active screening program for methicillin-resistant S. aureus (MRSA) in the surgical intensive care unit (ICU) was implemented in 1986. Between 1992 and 2001, only 6 patients with MRSA were admitted to the surgical ICU. However, 4 of these 6 strains were able to spread to 23 other patients and 15 healthcare workers (HCWs). We were surprised by the epidemic behavior of these strains and wondered whether this was exceptional for S. aureus or whether methicillin-susceptible S. aureus (MSSA) was also spreading in the ICU.

Design: A 2-month, prospective, observational study to investigate the incidence and spread of MSSA in the surgical ICU of UMCU and historical data collected during a 10-year period regarding MRSA.

Setting: A 10-bed surgical ICU in a 1,042-bed teaching hospital.

Results: Weekly swabs revealed the presence of MSSA in 11 (24%) of 45 patients and 16 (22%) of 72 HCWs. Of all 4,105 patient-HCW contacts, there were only 21 episodes in which both the patient and the HCW were found to carry MSSA. With the use of pulsed-field gel electrophoresis, no identical strains could be identified.

Conclusion: In our surgical ICU, MRSA seems to spread more easily than MSSA, probably because of selection under antibiotic pressure or a still unknown intrinsic factor within MRSA.