Urinary Tract Infection
Infection of the normally sterile urinary tract, usually by ascending gut bacteria, whose site of infection (bladder versus kidney) and host factors dictate how it presents and how aggressively it must be treated.
In a nutshell
Above the urethra the urinary tract is sterile, defended mechanically by the downward flush of urine. Infection is a breach of that flush by ascending gut bacteria. Where it sits (bladder or kidney) and who the host is determine how it presents and how hard it must be treated.
Classic presentation
A non-pregnant woman with dysuria, frequency, urgency and suprapubic discomfort and no fever; or, once the kidney is involved, fever, rigors and loin pain.
Key points
- The primary defence is flow, not immunity. Anything that impairs flushing (stasis, obstruction, catheters, the ureteric slowing of pregnancy) raises risk.
- The short female urethra sits close to the perineal reservoir of gut flora, which alone explains the marked female predominance.
- Cystitis is local: dysuria, frequency, urgency, suprapubic pain, with minimal systemic upset. Pyelonephritis adds fever, rigors and loin pain.
- Dipstick supports the diagnosis in younger non-pregnant women and is unreliable in older and catheterised patients, where it should not drive treatment.
- Send a midstream urine culture in pregnancy, in men, in children, on treatment failure, and in suspected pyelonephritis.
- Asymptomatic bacteriuria is treated in pregnancy, because of the risk of ascending pyelonephritis and preterm labour, and not treated in most non-pregnant older adults.
- A UTI in a man or a child is complicated by definition: culture-guided therapy, a longer course, and investigation.
First-line investigation
Urine dipstick in a younger non-pregnant woman; a midstream urine culture in pregnancy, men, children, treatment failure or suspected pyelonephritis.
First-line management
A short course of a first-line antibiotic guided by local resistance patterns for a simple lower UTI in a healthy non-pregnant woman, with hydration and analgesia.
Exam traps
- New confusion or a fall in an older adult with a positive dipstick is not automatically a UTI. Dipstick is unreliable in that group and asymptomatic bacteriuria is common.
- Asymptomatic bacteriuria in pregnancy is treated. In a non-pregnant older adult it is not.
- Loin pain with vomiting and fever may be an obstructed infected kidney: a urological emergency, not a prescription.
Educational content pending clinical review. Not medical advice.