Lower Urinary Tract Infection

Lower urinary tract infections (UTIs) involve infection in the bladder, causing cystitis (inflammation of the bladder). They can spread up to the kidneys and cause pyelonephritis. Urinary tract infections are far more common in women, where the urethra is much shorter, making it easy for bacteria to get into the bladder.

The primary source of bacteria for urinary tract infections is from the faeces. Normal intestinal bacteria, such as E. coli, can easily make the short journey to the urethral opening from the anus. Sexual activity is a crucial method for spreading bacteria around the perineum. Incontinence or poor hygiene can also contribute to the development of UTIs.

Urinary catheters are a key source of infection, and catheter-associated urinary tract infections tend to be more significant and challenging to treat.



Lower urinary tract infections present with:

  • Dysuria (pain, stinging or burning when passing urine)
  • Suprapubic pain or discomfort
  • Frequency
  • Urgency
  • Incontinence
  • Haematuria
  • Cloudy or foul smelling urine
  • Confusion is commonly the only symptom in older and frail patients


TOM TIP: It is important to distinguish between patients with a lower urinary tract infection and those with pyelonephritis. Pyelonephritis is generally a more serious condition with significant complications, including sepsis and kidney scarring. Suspect pyelonephritis in patients with:

  • Fever
  • Loin/back pain
  • Nausea/vomiting 
  • Renal angle tenderness on examination 


Urine Dipstick

Nitrites – gram-negative bacteria (such as E. coli) break down nitrates, a normal waste product in urine, into nitrites. The presence of nitrites suggest bacteria in the urine.

Leukocytes are white blood cells. It is normal to have a small number of leukocytes in the urine, but a significant rise can result from an infection or other cause of inflammation. Leukocyte esterase is tested on a urine dipstick, which is a product of leukocytes and indicates the number of leukocytes in the urine.

Red blood cells in the urine indicate blood. Microscopic haematuria is where blood is identified on a urine dipstick but not seen when looking at the sample. Macroscopic haematuria is where blood is visible in the urine. Haematuria is a common sign of infection but can also be present with other causes, such as bladder cancer or nephritis.

Nitrites are a better indication of infection than leukocytes. The NICE clinical knowledge summaries (2020) suggest that the presence of nitrites or leukocytes plus red blood cells indicate that the patient is likely to have a UTI.

If both are present, the patient requires treatment for a UTI. If only nitrites are present, it is worth treating as a UTI. If only leukocytes are present, the patient should not be treated as a UTI unless there is clinical evidence they have one.

midstream urine (MSU) sample sent for microscopy, culture and sensitivity testing will determine the infective organism and the antibiotics that will be effective in treatment. Not all patients with an uncomplicated UTI require an MSU. This is important in: 

  • Pregnant patients
  • Patients with recurrent UTIs
  • Atypical symptoms
  • When symptoms do not improve with antibiotics



The most common cause of UTI is Escherichia coli. E. coli are gram-negative, anaerobic, rod-shaped bacteria that are part of the normal lower intestinal microbiome. It is found in faeces and can easily spread to the bladder.

Other causes:

  • Klebsiella pneumoniae (gram-negative anaerobic rod)
  • Enterococcus
  • Pseudomonas aeruginosa
  • Staphylococcus saprophyticus
  • Candida albicans (fungal)


Antibiotics Choice

Follow local guidelines. An appropriate initial antibiotic in the community would be:

  • Trimethoprim (often associated with high rates of bacterial resistance)
  • Nitrofurantoin (avoided in patients with an eGFR <45)



  • Pivmecillinam
  • Amoxicillin
  • Cefalexin


Duration of Antibiotics

  • 3 days of antibiotics for simple lower urinary tract infections in women
  • 5-10 days of antibiotics for immunosuppressed women, abnormal anatomy or impaired kidney function
  • 7 days of antibiotics for men, pregnant women or catheter-related UTIs


It is worth noting that NICE recommend changing the catheter when someone is diagnosed with a catheter-related urinary tract infection.



Urinary tract infections in pregnancy increase the risk of pyelonephritispremature rupture of membranes and pre-term labour.


Management in Pregnancy

Urinary tract infection in pregnancy requires 7 days of antibiotics. All women should have an MSU for microscopy, culture and sensitivity testing.

The antibiotic options are:

  • Nitrofurantoin (avoid in the third trimester)
  • Amoxicillin (only after sensitivities are known)
  • Cefalexin


Nitrofurantoin needs to be avoided in the third trimester as there is a risk of neonatal haemolysis (destruction of the neonatal red blood cells).

Trimethoprim needs to be avoided in the first trimester as it works as a folate antagonist. Folate is essential in early pregnancy for the normal development of the fetus. Trimethoprim in early pregnancy can cause congenital malformations, particularly neural tube defects (e.g., spina bifida). It is not known to be harmful later in pregnancy but is generally avoided unless necessary.


Last updated May 2021
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