Urinary tract infections

Written by Tashi Maseland

Last Reviewed: August 2019

Review Due: August 2020



​UTIs (Urinary Tract Infections) can be classified in a number of ways:

  • Upper UTI - Pyelonephritis

  • Lower UTI - Cystitis or Prostatitis

  • Uncomplicated UTIs - Occur in otherwise healthy patients

  • Complicated UTIs - Occur in men, pregnant women or patients with underlying functional or structural abnormalities of the urinary tract or other conditions which predispose to infection



Bacteria from the bowel and vaginal flora (typically anaerobes and gram-negative bacteria) are the most common organisms causing UTIs. E.coli accounts for the vast majority (75-90%) of cases.

risk factors3

Female sex

Presence of a foreign body (e.g. catheter)

Sexual intercourse

Spermicide use

Abnormal bladder function (e.g. neurological disease)

Urinary tract blockage (e.g. by stones or prostatic hypertrophy)

History of recurrent UTI



Underlying disease (e.g. diabetes mellitus)


Urinary frequency


Urinary urgency

Suprapubic pain

Cloudy, blood-stained or pungent urine

Fever and flank pain (in pyelonephritis)



Pathogens colonise the urinary tract by one of two routes: ascending infection or haematogenous infection.

95% of UTIs are caused by ascending infection, whereby bacteria enter the distal urinary tract and ascend via the urethra to the bladder causing cystitis or to the kidneys causing pyelonephritis. Bacteria are normally flushed away by the passage of urine as the bladder empties. Urine stasis of any cause thus impairs the host defence against urinary tract colonisation. 


Women are more susceptible to UTIs as they have a shorter urethra. The urethra is also in close proximity to the vagina and anus, both of which are colonised with bacteria. Sexual intercourse can spread bacteria to the urethra, making it a common condition in young females. Susceptibility to UTIs varies among women depending on a variety of host and bacterial factors.


Rarely, pathogens from a distal site in the body may spread to the kidneys from the bloodstream (haematogenous infection). This leads to involvement of the renal parenchyma.



A diagnosis of UTI can often be made clinically with appropriate history and examination findings. Further investigation may be of benefit in some patients.


Urine dipstick may show evidence of nitrites, leukocytes or protein. A negative dipstick result does not exclude UTI, but significantly reduces the probability.

Mid-Stream Specimen of Urine (MSSU) Culture

A result of >10   colony forming units (cfu)/ml is typically diagnostic. The specimen can also be used to establish antibiotic sensitivities. A culture isn't typically required in non-pregnant women, but should be considered in children, men and pregnant women.

Blood Tests

FBC and CRP - For signs of raised inflammatory markers

Blood Cultures - If evidence of systemic infection


Patients who fail to respond to treatment, have recurrent UTIs, or have unusual organisms/symptoms may require referral to urology for consideration of ultrasound, cystoscopy or CT.



Do not treat asymptomatic bacteriuria in men, catheterised patients and non-pregnant women.

Note that the below antibiotics guidelines are based on the NHS GGC antimicrobial handbook. Always consult local guidelines for the correct dosing and antibiotic information.

Non-Pregnant Women

Uncomplicated Lower UTI: Nitrofurantoin or Trimethoprim for 3 Days

Upper UTI without Sepsis: Ciprofloxacin or Trimethoprim for 7 Days

Upper UTI with Sepsis: IV Gentamicin for 3-4 Days or if eGFR<20 then Temocillin/Ciprofloxacin for 7 Days

Pregnant Women

Asymptomatic Bacteriuria: Nitrofurantoin or Trimethoprim for 7 Days

Lower UTI without Sepsis: 1st/2nd Trimester: Nitrofurantoin/Trimethoprim/Cefalexin for 7 Days, 3rd Trimester: Trimethoprim/Cefalexin

Upper UTI without Sepsis: Co-Amoxiclav or Trimethoprim for 14 Days

Upper UTI with Sepsis: IV Co-Amoxiclav +/- IV Gentamicin for 14 Day


Uncomplicated Lower UTI: Nitrofurantoin or Trimethoprim for 7 Days

Prostatitis: Ciprofloxacin or Trimethoprim for 28 Days

Epididymitis/Orchitis: Ofloxacin for 14 Days

Upper UTI without Sepsis: Ciprofloxacin or Trimethoprim for 7 Days

Upper UTI with Sepsis: IV Gentamicin for 3-4 Days or if eGFR<20 then Temocillin/Ciprofloxacin for 7 Days

Catheterised Patients

Symptomatic Bacteriuria without Sepsis: Replace Catheter with Single Dose IV Gentamicin

Symptomatic Bacteriuria with Sepsis: Replace Catheter with Single Dose IV Gentamicin - Rx According to Sensitivities



UTIs are one of the most common conditions seen in primary care. 

They are much more common in women than men, with roughly 10% of women over 18 experiencing at least one suspected UTI annually. Of the women who develop a UTI, 20% to 40% experience recurrent UTIs.