MDR UTIs in pregnancy prone to progressing to pyelonephritis

Pregnant women with urinary tract infections (UTIs) caused by multidrug-resistant (MDR) bacteria may be at increased risk of developing pyelonephritis, according to a single-centre, retrospective study presented at SMFM 2020.

Included in the study were 215 pregnant women with lower UTIs (asymptomatic bacteriuria or acute cystitis) with gram-negative urine cultures. Of these, 52 women had cultures positive for antibiotic-resistant (AR; resistant to one to two antibiotic classes) bacteria, 51 positive for MDR bacteria (resistant to ≥3 antibiotic classes), and 112 positive for antibiotic-susceptible (AS) bacteria.

The likelihood of progressing to pyelonephritis was higher among women with MDR UTIS compared with those with AS UTIs (43.1 percent vs 19.6 percent; adjusted* odds ratio [adjOR], 3.50, 95 percent confidence interval [CI], 1.63–7.53; p=0.001). [SMFM 2020, abstract 1069]

Women with AR UTIs also had a higher risk of developing pyelonephritis than those with AS UTIs, but the results were not significant (30.8 percent vs 19.6 percent; adjOR, 2.07, 95 percent CI, 0.94–4.53; p=0.07).

Duration of hospitalization for pyelonephritis did not differ between the three groups (3, 2, and 4 days for women with AS, AR, and MDR infections, respectively), nor did incidence of pyelonephritis-related complications (sepsis, ICU admission, and renal abscess; two, zero, and one event in the respective groups).

“In an age of increasing antibiotic resistance, it is concerning that pregnant women with MDR gram-negative lower UTIs are at increased risk for developing pyelonephritis,” said the researchers from Duke University in Durham, North Carolina, US, noting the importance of future research in identifying the consequences of this finding.

Does bacterial virulence affect pyelonephritis incidence?

The researchers also conducted a separate retrospective study to identify whether virulence of bacteria could potentially increase the risk of pyelonephritis in pregnant women. The study cohort comprised 301 pregnant women with lower UTIs, of whom 164 and 36 had infections caused by Escherichia coli (E. coli) and virulent organisms**, respectively.

Women with lower UTIs caused by more virulent organisms did not have a higher risk of progressing to pyelonephritis compared with women with lower UTIs caused by E. coli (11.1 percent vs 17.3 percent; p=0.46; adjOR***, 0.74, 95 percent CI, 0.23–2.41). [SMFM 2020, abstract 470]

There was also no difference between virulent and E. coli-caused lower UTIs in terms of duration of hospitalization >6 days, preterm birth, low birth weight (LBW), sepsis, or anaemia (p>0.99 for all).

However, in a separate analysis, researchers from the same institution noted that lower UTIs caused by group B streptococcus (GBS) were less likely to progress to pyelonephritis than those caused by E. coli (3.5 percent vs 30.7 percent; p<0.001; adjOR^#, 0.13, 95 percent CI, 0.05–0.40). [SMFM 2020, abstract 490]

Outcomes such as duration of hospitalization due to pyelonephritis, anaemia, sepsis, preterm birth, LBW, and gestational age at delivery did not significantly differ between groups.

This retrospective study included 378 pregnant women with lower UTIs, of whom 116 and 166 had UTIs due to GBS and E. coli, respectively.

“Virulent lower UTIs in pregnancy do not progress to pyelonephritis at higher rates than E. coli and are associated with similar pyelonephritis-related morbidity,” said the researchers. “[However], E. coli infections progress to pyelonephritis in pregnancy at markedly higher rates than GBS,” they said.