Urinary Tract Infection (UTI) in Adults
NICE guideline [NG109] Urinary tract infection (lower): antimicrobial prescribing. Published: Oct 2018.
NICE CKS Urinary tract infection (lower) – men. Last revised: Apr 2025.
NICE CKS Urinary tract infection (lower) – women. Last revised: Feb 2025.
UK Health Security Agency Guidance Diagnosis of urinary tract infections: quick reference tools for primary care. Last updated: Jul 2025.
Minor restructuring of the article, taking the UK Health Security Agency guidance into account.
Date: 11/11/25
The scope of this article is to cover lower UTIs, but not upper UTIs (which is covered in the Acute Pyelonephritis article)
Background Information
Definition
A UTI can be either lower or upper:
- Lower UTI: infection of the bladder (cystitis), caused by bacteria from the GI tract entering the urethra
- Upper UTI: infection of the upper urinary tract (ureters and kidneys) – also known as pyelonephritis (see the Acute Pyelonephritis article for more information)
Bacteriuria is different from UTI:
- Bacteriuria refers to the presence of bacteria in the urine (detected on urinalysis or culture) and may occur with or without symptoms.
- When bacteriuria is accompanied by urinary symptoms, this represents a UTI
- Asymptomatic bacteriuria is the presence of significant bacteriuria without urinary symptoms
- It represents commensal colonisation, not a UTI, and does not require treatment
- Exceptions: treatment is indicated in pregnant women (see management section below)
Causative Agent
Most common: Escherichia coli (more common in females than males)
Some other causes:
- Staphylococcus saprophyticus (5-10% in females)
- Proteus mirabilis (associated with renal stones)
- Pseudomonas aeruginosa – associated with structural abnormality or permanent urethral catheterisation
- Enterobacter spp. – associated with instrumentation and catheterisation
Risk Factors
| General risk factors |
|
| Causes of ↓ urine flow |
|
| Causes of ↑ bacterial growth |
|
Clinical Features
Typical features of a lower UTI:
- Urinary frequency and urgency
- Dysuria
- Nocturia
- Cloudy urine
- Suprapubic pain / discomfort / tenderness
- Haematuria (possible but not always)
- Low-grade fever
The 3 key diagnostic signs / symptoms (outlined by UK HSA):
- Dysuria
- New nocturia
- Cloudy urine (to the naked eye)
Elderly with UTI may present vaguely:
- Delirium
- Loss of diabetes control
- General decline (e.g. worsening lethargy, reduced appetite)
Features suggestive of an upper UTI (pyelonephritis):
- Flank pain / +ve renal punch
- Nausea / vomiting
- Systemic upset (rigors / fever / flu-like illness)
Diagnosis
Diagnostic Approach
There are 3 main patient populations that determine the approach:
| <65 y/o | Female | Patient has 2 or 3 of the key diagnostic features → UTI is likely (urine dipstick is NOT necessary)
Patient has 1 or none of the key diagnostic features → perform urine dipstick |
| Male | Perform urine culture and sensitivity (do not use urine dipstick to diagnose UTI in males) | |
| >65 y/o | Perform urine culture and sensitivity (do not use urine dipstick to diagnose UTI) | |
| Suspected catheter-associated UTI | ||
Investigation and Diagnosis
Always perform a pregnancy test in females of reproductive age to exclude pregnancy
Urine Dipstick
Urine dipstick is often performed as an initial test, but it has a limited diagnostic role.
Interpretation of urine dipstick findings:
- +ve nitrite / leukocyte and +ve RBC → UTI likely
- -ve nitrite but +ve leukocyte → UTI is equally likely to other diagnoses
- -ve nitrite / leukocyte / RBC → UTI unlikely
Urine dipstick should NOT be used to diagnose UTI in:
- Male
- >65 y/o (less reliable due to increasing levels of asymptomatic bacteriuria)
- Suspected catheter-associated UTI (as most will have bacteriuria but without infection)
Urine Culture
Urine culture and sensitivity are required to diagnose UTI in the following patients:
- Male (all patients)
- Female
- >65 y/o
- All pregnant women
- Persistent symptoms (not resolving with antibiotics or recurring within 4 weeks after antibiotics)
- History of recurrent UTI
- Haematuria (visible or non-visible)
- Urinary catheter in situ / catheterised within the past 48 hours
Urine collection method:
- Preferred: morning mid-stream urine
- Catheter urine sample if there is a long-term indwelling catheter
Red Flags and Referral Indications
Refer with suspected bladder cancer pathway if:
- ≥45 y/o with unexplained visible haematuria in the absence of UTI / persisting or recurring after UTI treatment, OR
- ≥60 y/o with unexplained non-visible haematuria + dysuria / ↑
Consider non-urgent referral if:
- ≥60 y/o + recurrent / persistent unexplained UTI
Acute UTI Management
Conservative / General Management
Lifestyle advice:
- Drink enough fluids to avoid dehydration
- Empty bladder regularly (do not withhold urination urge)
- Void after sexual intercourse
- Wipe from front to back (to avoid peri-anal contamination)
Offer analgesia (paracetamol / ibuprofen)
Antibiotic Therapy
Note that asymptomatic bacteriuria does NOT require antibiotic therapy, with the exception of pregnant women.
Summary of antibiotic duration in various patient populations:
- Unpregnant female = 3 days
- Everyone else (i.e. pregnant females, males, catheterised patients) = 7 days
Male
1st line: 7-day course of:
- Trimethoprim 200mg BD, or
- Nitrofurantoin MR 100mg BD (if MR unavailable: 50mg QDS)
Nitrofurantoin should be avoided if eGFR <45 (use trimethoprim instead)
Female
Non-Pregnant Female
1st line: 3-day course of:
- Trimethoprim 200mg BD, or
- Nitrofurantoin MR 100mg BD (if MR unavailable: 50mg QDS)
2nd line:
- Pivmecillinam for 3 days
- Fosfomycin 3g single dose
Nitrofurantoin should be avoided if eGFR <45 (use trimethoprim instead)
A back-up antibiotic prescription (vs immediate prescription) can be considered for non-pregnant females (and without any risk factors for complicated UTI) with mild symptoms.
Treatment is started if:
- Symptoms do not start to improve within 48 hours OR
- Worsen at any time
NB – back-up prescriptions are NOT recommended for UTI in males, catheterised patients, or women who are pregnant OR have risk factors for complicated UTI
Pregnant Female
Antibiotics should be offered in both active UTI (i.e. symptomatic) or asymptomatic bacteriuria (usually identified through routine urinalysis)
Offer a 7-day course of antibiotics. Choice of antibiotic depends on the trimester:
| 1st / 2nd trimester | 1st line: nitrofurantoin MR 100mg BD (if MR unavailable: 50mg QDS)
Avoid nitrofurantoin at 3rd trimester, due to risk of neonatal haemolysis |
| 3rd trimester | 1st line: amoxicillin / cefalexin
Both are safe in ALL trimesters (can be used if nitrofurantoin is not appropriate in 1st / 2nd trimester) |
In pregnant females, a repeat urine sample for culture and susceptibility testing is necessary once antibiotic treatment is completed (to ensure clearance of infection)
DO NOT offer trimethoprim in pregnancy.
However, it’s the other way round in breastfeeding:
- Do not offer nitrofurantoin during breastfeeding
- Offer trimethoprim instead
Indwelling Catheter Patients
Offer a 7-day course of antibiotics
- 1st line: nitrofurantoin / trimethoprim / amoxicillin
- Also take previous urine culture and susceptibility results and local antimicrobial resistance data into account
Also:
- Check the catheter that is correctly positioned, drains properly and is not blocked
- Remove or change the catheter if it has been in situ for >7 days
Nitrofurantoin should be avoided if eGFR <45 (use trimethoprim instead)
Catheter-associated UTI is often polymicrobial, it is important to review culture and sensitivity results to guide antibiotic therapy.
Recurrent UTI Management Guidelines
Definition
Recurrent UTI definition:
- ≥3 UTI in the past 12 months, or
- ≥2 UTI in the past 6 months
Aetiology
Female is a major risk factor due to the short urethra.
Possible contributing factors: [Ref1][Ref2]
- Diabetes mellitus or those who take SGLT-2 inhibitors (both cause glycosuria, which is favourable for bacterial growth)
- Indwelling / intermittent urinary catheterisation
- Colovesical fistula (often from diverticular disease)
- Structural anomalies (urinary outflow obstruction → urine stasis)
- Vesicoureteral reflux (mainly in children)
- Urinary tract obstruction (BPH, prostate cancer, bladder cancer, urinary tract calculi)
- Bladder diverticula
- Neurogenic bladder
- Congenital anomalies (e.g. ureteral duplication / triplication)
- Cystocele (mainly in post-menopausal women)
Recurrent UTIs in females are generally less concerning and more often attributable to anatomical factors (short urethra) and physiological factors (e.g. periurethral colonisation, sexual activity etc.)
However, in males, recurrent UTIs are more likely to be due to an underlying cause.
Investigation and Diagnosis
Work-up should be individualised based on the patient’s sex, age, and clinical context
- Males typically require a more extensive work-up (as explained above)
- Healthy women with typical symptoms who respond promptly to therapy, routine imaging is typically not necessary
Investigations include:
- Cystoscopy
- Renal ultrasound
- CT urography
- Post-void residual measurement
Management
General / Conservative Management
Provide the following lifestyle advice:
- Drink enough fluids to avoid dehydration
- Empty bladder regularly (do not withhold urination urge)
- Void after sexual intercourse
- Wipe from front to back (to avoid peri-anal contamination)
- Avoid douching (in females)
Pharmacological Management
Ensure any current UTI has been treated based on culture results
Consider the following long-term management:
- 1st line: low-dose antibiotic prophylaxis
- 1st line: trimethoprim / nitrofurantoin
- Single-dose prophylaxis when exposed to a trigger, or low-dose daily prophylaxis (dose to be taken at night)
- 2nd line: methenamine hippurate (twice daily) as an alternative to daily antibiotic prophylaxis
- MoA: decomposes in acidic urine to release formaldehyde which has bactericidal effects
References