Increasing prevalence and associated risk factors for methicillin resistant Staphylococcus aureus bacteriuria

Infections due to methicillin resistant Staphylococcus aureus are becoming increasingly prevalent in hospitals and in the community. We reviewed our institutional experience to determine whether methicillin resistant S. aureus is becoming a more common cause of bacteriuria and to determine if there are specific risk factors that may predict the development of methicillin resistant S. aureus bacteriuria.

We reviewed all urine cultures with a pure growth of a single organism obtained at our institution from 1997 and 2007. Patients with urine cultures positive for methicillin resistant S. aureus were compared to a cohort with cultures positive for methicillin sensitive S. aureus, and to a third cohort with cultures positive for Escherichia coli to determine patient characteristics and associated risk factors.

We identified 7,100 and 9,985 positive urine cultures performed in 1997 and 2007, respectively. The most common urinary organism was E. coli. The number of patients with methicillin resistant S. aureus bacteriuria increased from 18 (0.3%) to 74 (0.8%) (p <0.001). On multivariate analysis older age (p = 0.004), catheter use (p = 0.004), hospital exposure (p <0.001) and patient comorbidity (p <0.001) were associated with methicillin resistant S. aureus bacteriuria compared with E. coli bacteriuria.

Methicillin resistant S. aureus remains rare as a cause of bacteriuria but its incidence has increased during the last decade. Risk factors for methicillin resistant S. aureus bacteriuria include increased age, patient comorbidity, hospital exposure and catheter use. For patients with these risk factors and new onset urinary symptoms, methicillin resistant S. aureus should be considered a possible cause of urinary tract infection.