Primary Staphylococcus aureus urinary tract infection: the role of undetected hematogenous seeding of the urinary tract

Staphylococcus aureus (SA) bacteriuria may accompany SA bacteremia, but primary SA urinary tract infection (UTI) may also occur. Our clinical observation of SA UTIs following intravenous catheter-related phlebitis lead us to review hematogenous and ascending route-related risk factors in patients with primary SA UTIs. The charts from all patients with SA UTIs over a 1.5-year period were reviewed for concurrent or recent hospitalization, intravenous catheterization, and for known UTI risk factors. Patients with concurrent SA bacteremia were excluded. Patients with Escherichia coli UTIs during the same period were included as controls. Twenty cases of primary SA UTI were compared with 43 E. coli UTI cases and they did not differ in age, diabetes mellitus, prostatic hypertrophy, previous UTI, or other urinary tract (UT) abnormality. However, cases were more likely than controls to have had recent or concurrent hospitalization, UT catheterization, and history of recent phlebitis. In multivariate analysis, UT catheterization and recent hospitalization retained significant association with SA UTI. Similar results were shown for the methicillin-resistant SA UTI subgroup. Even though UT catheterization is the main predisposing factor for primary SA UTI, some cases may be mediated through unrecognized preceding bacteremia related to intravascular device exposure or other healthcare-related factors.