Decreased invasive capacity of quinolone-resistant Escherichia coli in patients with urinary tract infections

Quinolone-resistant (QR) Escherichia coli may have lower invasive capacity than does quinolone-susceptible E. coli. To evaluate this, we prospectively collected data regarding all cases of E. coli invasive urinary tract infec tions (IUTI) in 669 adults admitted to the Infectious Diseases Unit of our hospital during a 3-year period, as well as 10,950 patients with cystitis o r asymptomatic bacteriuria who presented to the outpatient clinic during a 1-year period. QR E. coli was isolated in 20% of patients with cystitis, co mpared with 8% of those with IUTI (P<.05). The proportion of E. coli isolat es that were quinolone resistant was similar in patients with bacteremic an d nonbacteremic IUTI. The factors of urinary manipulation and structural ab normalities were independently associated with the presence of quinolone re sistance. Old age was the only variable independently associated with blood invasion. QR E. coli is less likely to produce invasive disease (pyeloneph ritis and prostatitis) than is quinolone-susceptible E. coli. However, once pyelonephritis or prostatitis have developed, there is no difference in th e incidence of bacteremia.