Aetiology of UTI in adults

Bonkat, 2024Chu, 2018Hooton, 2013van Nieuwkoop, 2017

In adult patients who do not have a functional or anatomical abnormality of the urinary tract, the most common cause of urinary tract infection (UTI) is Escherichia coli (70 to 95% of cases). Other bacterial pathogens (eg Klebsiella and Proteusspecies) each cause less than 5% of cases of UTI. Enterococcus species and Streptococcus agalactiae (group B streptococcus [GBS]), although isolated in urine, are rarely the causative pathogens in premenopausal womenHooton, 2013; however, consideration of GBS is important when treating UTI in pregnant patients because of an increased risk of invasive infectionBowyer, 2017Chu, 2018Hall, 2017Schafer, 2020The American College of Obstetricians and Gynaecologists (ACOG), 2023. Staphylococcus saprophyticus, while seen in cystitis, is rarely associated with pyelonephritis.

In adult patients with anatomical or functional abnormalities (eg neurogenic bladder, nephrolithiasis), E. coli is the most common cause of UTI, but a wider range of bacteria (eg Klebsiella, Proteus and Pseudomonas species) also cause infection and can be associated with invasive disease. Consider expert advice for the management of patients with anatomical or functional abnormalities.

Symptomatic fungal UTI is uncommon; see Candiduria and UTI caused by Candida and related species in adults.