Bacteremia complicating gram-negative urinary tract infections: a population-based study

Abstract

Background: Urinary tract infection (UTI) is common and bacteremia complicating this infection is frequently seen. There has been limited data published that characterize bacteremic UTI in a population-based setting over an extended period. We therefore examined the incidence rate, microbiology, outcome, and in vitro antimicrobial resistance trends of bacteremic UTI due to gram-negative bacilli in Olmsted County, Minnesota, from 1/1/1998 to 12/31/2007.

Methods: We used Kaplan-Meier method to estimate mortality rates, Cox proportional hazard regression to determine risk factors for mortality, and logistic regression to examine temporal changes in antimicrobial resistance rates.

Results: We identified 542 episodes of bacteremic gram-negative UTI among Olmsted County residents during the study period. The median age of patients was 71 years and 65.1% were females. The age-adjusted incidence rate per 100,000 person-years was 55.3 (95% confidence interval [CI]: 49.5-61.2) in females and 44.6 (95% CI: 38.1-51.1) in males. Escherichia coli was the most common pathogen (74.9%). The 28-day and 1-year all-cause mortality rates were 4.9% (95% CI: 3.0-6.8) and 15.6% (95% CI: 12.4-18.8), respectively. Older age was associated with higher mortality; community-acquired infection acquisition and E. coli UTI were both independently associated with lower mortality. During the study period, resistance rates increased linearly from 10% to 24% for trimethoprim-sulfamethoxazole and from 1% to 8% for ciprofloxacin.

Conclusions: To our knowledge, this is the first population-based study of bacteremic gram-negative UTI. The linear trend of increasing antimicrobial resistance among gram-negative isolates should be considered when empiric therapy is selected.

Figure 1

Incidence rate of bacteremic gram-negative urinary tract infection, by age and gender, 1998–2007.

Figure 2

Age- and gender-adjusted incidence rate of bacteremic gram-negative urinary tract infection, by calendar year. NOTE. Error bars indicate 95% confidence intervals.

Figure 3

Age-adjusted incidence rate of bacteremic urinary tract infection, by pathogen and gender. NOTE. Error bars indicate 95% confidence intervals. The six most common pathogens are included in the figure.

Figure 4

In vitro antimicrobial resistance rates of gram-negative bloodstream isolates, by calendar year. NOTE. TMP-SMX: trimethoprim-sulfamethoxazole. P-value denotes a one-degree of freedom test for linear trend using logistic regression.