Bad bugs: antibiotic-resistant bacteriuria in pregnancy and risk of pyelonephritis.

Background: The introduction of antibiotics has significantly reduced morbidity and mortality from microbial infections, but the rise of antibiotic-resistant and multidrug-resistant microbes is of increasing clinical concern. Few studies have examined the prevalence and impact of antibiotic resistance in common antenatal infections.

Objective: This study aimed to determine whether pregnant women with a urine culture positive for antibiotic-resistant or multidrug-resistant gram-negative bacteria are at increased risk of developing pyelonephritis than pregnant women infected with antibiotic-susceptible organisms.

Study Design: This was a retrospective cohort study of pregnant women with asymptomatic bacteriuria or acute cystitis from a single health system from July 2013 to May 2019. Women with gram-negative antibiotic-resistant (resistance to 1-2 antibiotic classes) and multidrug-resistant (resistance to ≥3 antibiotic classes) lower urinary tract infections were compared with women with antibiotic-susceptible urinary tract infections in terms of demographic, infectious, antepartum, and intrapartum data. The primary outcome was pyelonephritis, defined as a billing code for pyelonephritis plus fever or flank pain. The secondary outcomes were length of stay in the hospital because of pyelonephritis, a composite of pyelonephritis complications (renal abscess, sepsis, and intensive care unit admission), and preterm delivery. The differences in the primary outcome were analyzed using multivariate logistic regression.

Results: A total of 573 women were eligible for inclusion. Of the 573 women, 334 (58%) had gram-negative bacteria on urine culture. Of the 334 cases, 173 (52%) were antibiotic susceptible, 74 (22%) were antibiotic resistant, and 87 (26%) were multidrug resistant. Women with antibiotic-resistant and multidrug-resistant infections were more likely to have hypertension (P=.004), to be Black (P=.03), to have public insurance (P=.002), and to experience more urinary infections (P=.001). Pyelonephritis was more common in women with antibiotic-resistant (adjusted odds ratio, 2.27; 95% confidence interval, 1.08-4.78) and multidrug-resistant (adjusted odds ratio, 3.06; 95% confidence interval, 1.57-5.96) infections than in women with antibiotic-susceptible urinary tract infections. Length of stay, preterm delivery, and pyelonephritis complications did not differ between antibiotic-susceptible and antibiotic-resistant and multidrug-resistant infections.

Conclusion: In an age of increasing antibiotic resistance, more than one-half of pregnant women with bacteriuria experience at least 1 infection with an antibiotic-resistant organism. These resistance patterns have a real clinical impact as pregnant women with antibiotic-resistant gram-negative lower urinary tract infections have an estimated 2- to 3-fold increased odds of developing pyelonephritis.