Lower urinary tract infection

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Lower urinary tract infection is microbial inflammation confined clinically to bladder and urethra. The key boundary is absence of fever, flank pain, systemic toxicity or prostate features, which require a different diagnostic and treatment pathway.

Diagnosis should integrate symptoms, host group and pre-test probability rather than equating bacteriuria or dipstick positivity with infection. Catheterised patients and older adults commonly have asymptomatic colonisation.

Antibiotic duration and choice differ for non-pregnant women, pregnancy and men. Culture is particularly important where consequences, resistance or occult upper-tract or prostate involvement are greater.

Safe care for lower urinary tract infection depends on separating physiological instability from diagnostic uncertainty: resuscitation and infection-control actions proceed while targeted samples, imaging and source-control decisions are arranged.

Antimicrobial decisions in lower urinary tract infection should document indication, likely source, allergy phenotype, pregnancy possibility, renal and hepatic function, previous microbiology and the planned review or stop point.

Key points

Lower urinary tract infection causes dysuria, frequency, urgency and suprapubic discomfort without fever, flank pain or systemic illness.
In women under 65, a symptom-led diagnostic approach is useful; vaginal discharge or irritation makes urinary infection less likely.
Culture urine before treatment in pregnancy and men, and when recurrent, resistant-risk, atypical, severe or failing to improve.
Do not screen or treat asymptomatic bacteriuria except in pregnancy and before selected urological procedures breaching mucosa.
For non-pregnant women, NICE first choices include nitrofurantoin 100 mg modified-release twice daily for three days or trimethoprim 200 mg twice daily for three days when resistance risk is low.
Men generally need a seven-day course and assessment for prostate involvement; nitrofurantoin is unsuitable when prostatitis is suspected.
Use renal function, pregnancy, allergy, prior culture and recent antibiotic exposure to select a safe agent.
Escalate symptoms that worsen rapidly or fail to begin improving within 48 hours, and reconsider pyelonephritis, STI and structural disease.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Enteric Gram-negative organisms

Uropathogenic Escherichia coli causes most community lower urinary infections, while Klebsiella, Proteus and other Enterobacterales are more likely with structural or healthcare risk.

Bladder and voiding risk

Sexual activity, spermicide, menopause, incomplete emptying, prolapse, stones and instrumentation facilitate periurethral colonisation and ascending entry.

Resistance selection

Recent antibiotics, healthcare exposure, travel and previous resistant cultures increase the probability that standard empirical agents will be inactive.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Periurethral ascent
Enteric organisms colonise the periurethral region, ascend through the urethra and adhere to bladder urothelium using specialised fimbriae.
2
Mucosal inflammation
Innate immune recognition recruits neutrophils and produces dysuria, urgency, frequency, suprapubic pain, pyuria and microscopic haematuria.
3
Containment or progression
Host defence and treatment may confine infection to the bladder, while reflux, obstruction or virulent organisms permit ascent to renal tissue.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Typical cystitis symptoms

New dysuria, nocturia, frequency, urgency, cloudy urine visible to the patient and suprapubic discomfort support lower urinary infection.

Upper-tract boundaryRed flag

Fever, rigors, loin pain, vomiting or costovertebral-angle tenderness should be managed as possible pyelonephritis rather than uncomplicated cystitis.

Sepsis physiologyRed flag

Confusion, tachypnoea, hypotension, mottling, reduced urine output or elevated lactate requires urgent systemic assessment and hospital escalation.

Male and pregnancy contextRed flag

Pregnancy increases maternal and fetal consequences, while male symptoms raise concern for prostatic involvement, obstruction and a complicated urinary source.

Context changes probability

Recent healthcare exposure, antimicrobial use, travel, procedures, devices, pregnancy, immune compromise and previous resistant isolates materially change the likely diagnosis and treatment risk in lower urinary tract infection.

Red flags requiring action

Fever, rigors, flank pain or costovertebral-angle tenderness suggests upper urinary tract infection.
Hypotension, tachypnoea, confusion, mottling or oliguria requires urgent sepsis assessment.
Pregnancy with urinary symptoms or bacteriuria requires prompt culture-guided treatment and obstetric-aware follow-up.
Male urinary symptoms with pelvic pain, retention or systemic illness may reflect acute prostatitis.
Persistent visible haematuria, recurrent atypical infection or treatment failure requires investigation beyond repeated antibiotics.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Structured symptom assessmentFirst step
Why
Estimate lower UTI probability and identify upper-tract, genital or systemic features.
Interpretation and limitations
Multiple key urinary symptoms without vaginal discharge increase probability in women under 65; isolated cloudy or smelly urine is insufficient.
02
Urine dipstick in selected non-pregnant women
Why
Refine probability when symptoms do not already make the diagnosis clear.
Interpretation and limitations
Nitrite is relatively specific; leucocytes and blood are less specific. Do not use dipsticks to diagnose UTI in catheterised adults or older people without urinary symptoms.
03
Midstream urine culture and susceptibility
Why
Confirm organism and direct therapy in pregnancy, men, recurrence, treatment failure or resistant-risk disease.
Interpretation and limitations
Collect before antibiotics where possible. Mixed growth may represent contamination; interpret counts with symptoms, collection quality and prior treatment.
04
Pregnancy test
Why
Identify pregnancy when status is uncertain because antibiotic selection, duration and follow-up differ.
Interpretation and limitations
A positive result changes prescribing safety and strengthens the requirement for culture and post-treatment follow-up according to maternity pathways.
05
Renal function
Why
Check safe nitrofurantoin and other antimicrobial use when impairment is known or plausible.
Interpretation and limitations
Avoid nitrofurantoin when eGFR is below 45 mL/minute in most cases; selected short courses at 30 to 44 require cautious guideline-based justification.
06
STI testing and genital examination
Why
Investigate dysuria with discharge, sexual exposure, pelvic symptoms or sterile pyuria.
Interpretation and limitations
Use appropriate first-catch urine or self-taken swabs and manage partners and infection according to sexual-health guidance rather than repeated UTI therapy.
07
Host and prescribing assessment
Why
Identify modifiers that alter diagnostic yield, severity and safe prescribing for lower urinary tract infection.
Interpretation and limitations
For lower UTI, record allergy phenotype, eGFR, pregnancy, previous urine susceptibility, recent antimicrobial exposure, prostate features and interactions before selecting dose and duration.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Vaginitis or cervicitis

Discharge, irritation, dyspareunia and exposure history suggest Candida, bacterial vaginosis, chlamydia, gonorrhoea or trichomoniasis rather than isolated cystitis.

Pyelonephritis

Fever, rigors, vomiting, flank pain and costovertebral-angle tenderness indicate renal involvement requiring a tissue-active regimen and possible admission.

Urolithiasis or malignancy

Colicky pain, recurrent Proteus, persistent haematuria, weight loss or sterile pyuria requires imaging or urological investigation.

Bladder pain syndrome

Chronic pain related to bladder filling with repeatedly negative cultures suggests a non-infective syndrome rather than recurrent antibiotic failure.

Additional chapter-specific clues

Vaginal alternative features

Vaginal discharge, irritation or dyspareunia lowers cystitis probability and should prompt assessment for vaginitis, cervicitis and sexually transmitted infection.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01WOMANTreat uncomplicated lower infectionFirst stepA non-pregnant woman has a convincing lower urinary syndrome without systemic, flank or vaginal features.

1Assess symptom combination, previous cultures, resistance risk, renal function and immediate allergy and give self-care and safety-net advice.
2Use nitrofurantoin 100 mg modified-release twice daily for three days when eGFR is at least 45 mL/minute, or trimethoprim 200 mg twice daily for three days when resistance risk is low.
3When first choices are unsuitable, use the current NICE alternatives and local susceptibility data rather than extending a convenient but ineffective course.
4Review if symptoms worsen at any time or do not begin improving within 48 hours; culture and reconsider upper-tract, STI and non-infective causes.

02PREGNANCY OR MANCulture and use longer treatmentLower urinary symptoms occur during pregnancy or in an adult man without sepsis or clear prostate involvement.

1Obtain a midstream urine sample before antibiotics and assess immediately for pyelonephritis, retention, prostatitis and pregnancy-specific complications.
2In pregnancy use a seven-day pregnancy-compatible regimen selected from culture and current guidance; avoid trimethoprim in the first trimester and nitrofurantoin at term.
3In men use a seven-day regimen with susceptibility guidance and avoid nitrofurantoin when prostate involvement is suspected because tissue concentrations are inadequate.
4Review culture results, clinical response and the need for repeat pregnancy culture or urological assessment for recurrence, haematuria or obstruction.

03NO SYMPTOMSAvoid treating colonisationBacteria, leucocytes, nitrite or cloudy urine is found without attributable urinary or systemic symptoms.

1Confirm whether true urinary symptoms, pregnancy or an upcoming urological procedure breaching mucosa is present before labelling infection.
2Do not screen or prescribe for asymptomatic bacteriuria in most non-pregnant adults, including older and catheterised people.
3In pregnancy arrange culture-confirmed treatment and follow-up because untreated bacteriuria increases pyelonephritis and adverse pregnancy risk.
4Investigate another cause of delirium or functional decline rather than assigning causation to an incidental positive urine result.

04REASSESSReview response and diagnosisSymptoms persist, physiology worsens or expected improvement in lower urinary tract infection has not occurred.

1Repeat observations and examination, reconsider the anatomical source and look actively for obstruction, collection, perforation, ischaemia or another diagnosis complicating lower urinary tract infection.
2Review urine susceptibility, adherence, absorption, eGFR and medicine toxicity; change lower UTI treatment only when ongoing symptoms and the organism result justify a documented revision.
3EscalationEscalate to the relevant medical, surgical, microbiology, infection or public-health team when source control, resistant infection, outbreak management or specialist follow-up is required for lower urinary tract infection.
4Give urinary safety-net advice covering fever, rigors, flank pain, vomiting, retention, confusion, reduced urine output and the route for urgent reassessment.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

NICE first-choice treatment for susceptible lower urinary infection when renal function permits adequate urinary concentrations.

Nitrofurantoin modified release

Give 100 mg orally twice daily for three days in non-pregnant women or seven days in men when prostate involvement is not suspected.

Usually require eGFR at least 45 mL/minute; avoid for pyelonephritis, sepsis or prostatitis and near term in pregnancy, and counsel about pulmonary, hepatic, neurological and haemolytic toxicity.

NICE first-choice alternative for lower urinary infection where prior culture and local resistance support activity.

Trimethoprim

Give 200 mg orally twice daily for three days in non-pregnant women or seven days in men when resistance risk is low.

Avoid during the first trimester of pregnancy unless specifically advised; check renal function, potassium, folate status and interactions with methotrexate, warfarin, ACE inhibitors and spironolactone.

NICE second-choice beta-lactam option when first-choice lower UTI treatment is unsuitable or not active.

Pivmecillinam

Give 400 mg orally as the initial dose, then 200 mg orally three times daily to complete a three-day course in eligible non-pregnant women.

Clarify penicillin allergy, review renal function and culture susceptibility, and use the group-specific course length from current guidance rather than copying the three-day regimen into pregnancy or male infection.

Provides a single-dose second-choice option for selected uncomplicated lower urinary infection.

Fosfomycin

Give a single 3 g oral sachet for eligible non-pregnant women when current guidance and susceptibility support this option.

Do not use for pyelonephritis, sepsis or suspected prostatitis; review renal function, previous resistance, local formulary restrictions and persistent symptoms that require culture or anatomical assessment.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Ascending pyelonephritis

Untreated or resistant bladder infection can ascend to the renal pelvis and parenchyma, producing fever, flank pain and systemic illness.

Urosepsis

Bloodstream invasion from an infected urinary tract can cause vasoplegia, organ dysfunction and shock, especially with obstruction or frailty.

Pregnancy complications

Bacteriuria and infection in pregnancy increase pyelonephritis and adverse maternal or fetal outcomes, supporting culture-directed treatment and follow-up.

Resistance and adverse effects

Unnecessary or repeated antibiotics select resistant flora and expose patients to allergy, Clostridioides difficile infection and drug-specific organ toxicity.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Advise the patient to seek review if symptoms worsen at any time or do not start improving within 48 hours of antibiotics.
Review urine culture promptly and change treatment only when susceptibility, ongoing symptoms and clinical risk justify it.
Check renal function and potassium when impairment, older age or interacting medicines make treatment toxicity plausible.
In pregnancy confirm the local repeat-culture and antenatal follow-up plan after treatment.
Investigate recurrent infection for triggers, menopause-related factors, stones, incomplete emptying and resistant organisms before repeated empirical courses.
At every review of lower urinary tract infection, confirm that the working diagnosis still fits the trajectory and that microbiology or imaging has not revealed a source requiring a different intervention.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Symptoms outrank smell

Cloudy or malodorous urine is common with concentration and colonisation and does not independently establish symptomatic infection.

Nitrofurantoin stays in urine

Useful bladder concentrations do not translate into adequate renal parenchymal or prostate treatment, making anatomical classification essential.

Pregnancy changes the threshold

Asymptomatic bacteriuria is treated in pregnancy because the evidence and consequences differ from non-pregnant adult colonisation.

Male infection needs localisation

Pelvic pain, retention, fever or recurrent infection raises concern for acute prostatitis or obstruction and changes both agent and duration.

A negative nitrite is incomplete

Frequent voiding and organisms that do not reduce nitrate can produce a negative nitrite despite clinically plausible infection.

Document the decision boundary

For lower urinary tract infection, record why treatment, observation, admission, isolation or source control was chosen and which finding would trigger a change of plan.

11Common pitfallsFrequent interpretation and management errors.

01
Do not treat isolated confusion in an older adult as UTI solely because a urine dipstick or culture is positive.
02
Do not use nitrofurantoin for fever, flank pain, sepsis or suspected prostate infection because tissue exposure is inadequate.
03
Do not prescribe a three-day female cystitis course automatically for pregnancy or adult men.
04
Do not overlook vaginitis, urethritis, pelvic inflammatory disease, stones, malignancy or bladder pain syndrome when symptoms are atypical.
05
Do not leave a positive pregnancy culture without a documented treatment and follow-up plan.
06
Do not allow a positive colonisation-prone test, device sample or nonspecific inflammatory marker to outweigh the clinical syndrome when assessing lower urinary tract infection.