Clinical significance of bacteriuria with low colony counts of Enterococcus species

The clinical significance of low counts of enterococci in urine cultures remains unclear. The goal of this study was to investigate the clinical significance of enterococci growing in numbers lower than 100,000 colony-forming units per milliliter (cfu/ml) in urine samples. Clinical parameters were collected from patients whose midstream clean-catch urine samples grew Enterococcus spp. in amounts between ≥10,000 and 100,000 cfu/ml and who were not previously treated with antibiotics. Only those patients who had leukocyturia in addition to positive culture were considered to have true urinary tract infection (UTI). Of the 208 patients included in the study, 54% were diagnosed with true UTI. Patients with true UTI were older by 6 years (p=0.03), were more likely to be hospitalized (p=0.016), had higher rates of dysuria (p=0.0001), urgency (p=0.0001), and frequency (p=0.0001), and had more solid tumors (p=0.03). By multivariate analysis, urgency (OR=7.1) and hospitalization (OR=4.4) were identified as independent risk factors for true UTI with enterococci in low counts. Enterococcal counts in patients with true UTI were randomly distributed all along the scale between 10,000 and 100,000 cfu/ml, and no differential cutoff could be determined. In conclusion, more than half of the patients whose urine cultures grow Enterococcus spp. in counts lower than 100,000 cfu/ml may have true UTI, especially if they are hospitalized and have symptoms of dysuria, urgency, or frequency. Microbiology laboratories should perform a complete work-up on samples containing low counts of enterococci, and the final interpretation should be done by physicians, using additional clinical information.