Urinary Tract Infection and Progression to Pyelonephritis: Group B Streptococcus versus E. coli

Objective  Group B Streptococcus (GBS) colonization of the lower urinary tract in pregnancy is associated with severe infections such as chorioamnionitis, endometritis, and pyelonephritis. The objective of this study was to compare rates of progression to pyelonephritis between GBS and Escherichia coli lower urinary tract infections (LUTIs), as well as compare infectious and obstetric morbidity secondary to these pathogens. Study Design  Retrospective cohort of pregnant women with LUTIs (asymptomatic bacteria or acute cystitis [AC]) from a single health system between July 2013 and May 2019. Demographic, infectious, antepartum, and intrapartum data were abstracted from medical records of women with GBS or E. coli LUTI. The primary outcome was progression to pyelonephritis. Secondary outcomes included pyelonephritis-related anemia, sepsis, pyelonephritis length of stay (LOS), median gestational age (GA) at delivery, preterm delivery, and low birth weight (LBW). Logistic regression was used to calculate the adjusted odds of the primary outcome. Results  Of 729 pregnant women with urinary colonization, 433 were culture positive for one of the aforementioned bacteria, with 189 (43.6%) having GBS and 244 (56.4%) having E. coli. Women with E. coli were more likely to be younger, use tobacco, have a history of AC, and have a history of preterm birth. Rates of progression to pyelonephritis were markedly higher with E. coli (15.6%) than with GBS (1.1%; p  < 0.001). Median LOS for pyelonephritis and pyelonephritis-related morbidities did not differ. Median GA at delivery, preterm delivery, and LBW rates also did not differ. In adjusted analysis, controlling for history of AC, insurance status, tobacco use, prior preterm birth, primary infection type, and maternal age, women with GBS LUTI had markedly decreased odds of developing pyelonephritis in pregnancy compared with those with E. coli (adjusted odds ratio: 0.04, 95% confidence interval: 0.01-0.28). Conclusion   Escherichia coli infections progress to pyelonephritis in pregnancy at markedly higher rates than GBS, although obstetric outcomes are similar.