Urinary Tract Infections

Lower urinary tract infections (UTIs) involve infection in the bladder, causing cystitis (inflammation of the bladder).

Pyelonephritis refers to inflammation of the kidney resulting from bacterial infection. The inflammation affects the kidney tissue (parenchyma) and the renal pelvis (where the ureter joins the kidney).

Urinary tract infections are far more common in women, where the urethra is much shorter, making it easier for bacteria to get into the bladder.

The primary source of bacteria for urinary tract infections is faeces. Normal intestinal bacteria, such as E. coli, can easily 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 possible source of infection, and catheter-associated urinary tract infections tend to be more serious 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


Pyelonephritis has a similar presentation to lower urinary tract infections plus the additional triad of symptoms:

  • Fever
  • Loin or back pain (bilateral or unilateral)
  • Nausea or vomiting


Patients with pyelonephritis may also have:

  • Systemic illness
  • Loss of appetite
  • Haematuria
  • Renal angle tenderness on examination


TOM TIP: It is essential to distinguish between lower urinary tract infections and pyelonephritis. Pyelonephritis is a more severe condition with significant complications, including sepsis and kidney scarring. Suspect pyelonephritis in patients with:

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


Urine Dipstick

Nitrites on a dipstick test suggest bacteria in the urine. Gram-negative bacteria (e.g., E. coli) break down nitrates (a normal waste product in urine) into nitrites.

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 (a product of leukocytes) is tested on a urine dipstick, indicating the number of leukocytes in the urine.

Red blood cells in the urine indicate bleeding. Microscopic haematuria is where blood is seen 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 (June 2023) suggest that nitrites or leukocytes plus red blood cells indicate that the patient will likely have a UTI. The dipstick result is less reliable in catheterised patients or women over 65.

Where only nitrites are present, it is worth treating as a UTI. Where only leukocytes are present, a sample should be sent to the lab for further testing. Antibiotics may be considered where there is clinical evidence of a UTI.

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. An MSU 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, which are gram-negativeanaerobicrod-shaped bacteria. They are part of the lower intestinal microbiome and can easily spread from faeces to the bladder.

Other causes:

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


Management of Lower Urinary Tract Infections

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

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



  • Pivmecillinam
  • Amoxicillin
  • Cefalexin


The typical duration of antibiotics is:

  • 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.


Management of Pyelonephritis

Referral to hospital is required if there are features of sepsis or if it is unsafe to manage them in the community.

NICE guidelines (2018) recommend the following first-line antibiotics for 7-10 days when treating pyelonephritis in the community:

  • Cefalexin
  • Co-amoxiclav (if culture results are available)
  • Trimethoprim (if culture results are available)
  • Ciprofloxacin (keep tendon damage and lower seizure threshold in mind)


Patients admitted to hospital with sepsis require the sepsis six, which includes a serum lactate, blood cultures, urine output monitoring, oxygen, empirical broad-spectrum antibiotics and IV fluids.

Two things to keep in mind with patients that have significant symptoms or do not respond well to treatment are:

  • Renal abscess
  • Kidney stone obstructing the ureter, causing pyelonephritis



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 (avoided in the third trimester)
  • Amoxicillin (only after sensitivities are known)
  • Cefalexin (the typical choice)


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

Trimethoprim should 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 July 2023