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

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.

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.

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.

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.

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.