Methicillin-resistant Staphylococcus aureus infection acquired in intensive care: a prospective study of infection and outcome

Methicillin-resistant Staphylococcus aureus (MRSA) was first described in 1961 and has been associated with increasing health care associated infection and chronic ill health. This study was designed to examine the relationship between mortality and intensive care acquired MRSA infection.

Between the years 2000 and 2002, prospective data was collected from the intensive care database (Wardwatcher), the infection control database in our hospital and the regional MRSA reference laboratory. ICU-acquired MRSA infection was defined as MRSA infection diagnosed after 72 hours in the ICU. Any patient in whom the source of MRSA was questionable was included in the group where MRSA acquisition was attributed to the ICU.

During the period of the study 1107 patients were admitted to intensive care. Twelve patients without valid APACHE II scores were excluded from the study. The rate of ICU-acquired MRSA infection was 5.8%.

In the general ICU population the mean length of stay was 6.1 days. In the group with ICU-acquired MRSA infection the mean length of stay was 17.1 days. The mean time at which MRSA infection was acquired in the ICU was at 8.9 days.

Patients with ICU-acquired MRSA infections were compared with the general ICU population. Both groups had a mean APACHE II score of 22.5 and comparable mean predicted hospital mortality rates: 42.6% (MRSA group) and 42.2% (general group). Mean actual hospital mortality was 40.9% in the MRSA group and 41.6% in the general group.

In our unit, acquisition of MRSA infection during the ICU stay does not affect ICU outcome or hospital mortality. MRSA infection occurs in patients who have a longer than average length of stay in the ICU.