Lecture 6: Urinary Tract Infections (UTIs)

A set of Question-and-Answer flashcards covering key concepts from the Renal Case on UTIs (definitions, risk factors, diagnosis, pathogens, treatment options, special situations like pregnancy and catheter use, and practical management guidelines).

What is bacteriuria and how is it defined?

Presence of bacteria in urine, defined as >10^5 CFU/mL.

What is asymptomatic bacteriuria (ABU)?

Bacteriuria with no urinary symptoms; >10^5 CFU/mL of the same organism in two consecutive clean-catch MSU samples.

When should asymptomatic bacteriuria be treated?

Usually not treated, except in pregnancy where treatment is recommended due to complications.

List common risk factors for bacteriuria.

Female sex, sexual activity, older age, co-morbidities, nursing/care home residence, urinary catheter, pregnancy.

Differentiate LUTI and UUTI.

LUTI = lower urinary tract infection (cystitis), usually uncomplicated; UUTI = upper urinary tract infection (pyelonephritis), usually complicated.

What signs are typical of a LUTI?

Dysuria, frequency, urge to urinate, polyuria, fever, haematuria, foul-smelling urine; elderly may have confusion.

What signs indicate a UUTI (pyelonephritis)?

Loin pain, abdominal tenderness, often very unwell; may require hospital treatment.

How is UTI diagnosed in practice?

Consider the full clinical picture; use urine dipstick (leukocytes, nitrites, blood) and MSU with MC&S to confirm pathogens and sensitivities.

What does a urine dipstick test detect in UTIs?

Leukocytes, nitrites, and blood (haematuria); nitrites indicate presence of Gram-negative bacteria.

What are the advantages of urine dipstick testing?

Simple, non-invasive, cheap, quick, easy to perform.

What are the limitations of urine dipstick tests?

Very crude and non-specific; may be unreliable; should not be used alone to diagnose UTI.

What is the purpose of a clean catch MSU?

To obtain a purer culture by reducing contamination from genital flora; sample collected after cleaning the genital area.

Name common Gram-negative bacteria causing UTIs.

Escherichia coli (>70%), Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa.

Name common Gram-positive bacteria causing UTIs.

Enterococcus species and Staphylococcus saprophyticus.

List common drugs used to treat UTIs.

Nitrofurantoin, Trimethoprim, Gentamicin, Co-amoxiclav, Quinolones (ciprofloxacin), Pivmecillinam, Fosfomycin, Methenamine hippurate, Cephalexin.

What is the mechanism of action of nitrofurantoin?

Interferes with bacterial RNA/DNA synthesis.

Against which organisms is nitrofurantoin effective and which is it not?

Active against E. coli and many Gram-negatives; not effective against Pseudomonas.

When should nitrofurantoin be avoided due to renal function?

Do not use if eGFR < 45 mL/min; caution 30–44 mL/min for short courses; avoid in risk of peripheral neuropathy.

What is the usual nitrofurantoin dose regimen?

50 mg four times daily (QDS) or 100 mg MR tablets twice daily (BD).

What monitoring is recommended with long-term nitrofurantoin?

Monitor liver function and pulmonary symptoms, especially in the elderly.

What is the mechanism of action of trimethoprim?

Inhibits dihydrofolate reductase, blocking folic acid synthesis in bacteria.

Why is trimethoprim not always first-line for UTIs?

Resistance is increasing; sometimes restricted use to known sensitive organisms or specific settings; dose adjustments needed in renal impairment.

What monitoring is recommended for trimethoprim use?

Blood counts with long-term use; electrolytes (hyperkalaemia risk); renal function; consider plasma trimethoprim levels in long-term use.

What is pivmecillinam?

A penicillin-type, broad Gram-negative narrow-spectrum antibiotic used for LUTIs; monitor liver and renal function.

What is fosfomycin and how does it work?

Broad-spectrum, bactericidal; inhibits phosphoenolpyruvate transferase, blocking formation of N-acetylmuramic acid and peptidoglycan synthesis; used for lower UTIs; monitor electrolytes if IV.

How should fosfomycin granules be taken?

On an empty stomach; dissolve granules in water and take immediately, preferably before bedtime after emptying the bladder.

What is methenamine hippurate used for and how does it work?

Used for long-term prophylaxis/recurrent LUTIs; requires acidic urine; methenamine forms formaldehyde in acidic urine, with hippuric acid contributing to antibacterial effect.

Why treat asymptomatic bacteriuria in pregnancy and what duration?

To reduce risk of pyelonephritis (around 30% risk); duration typically 7 days of antibiotic therapy.

How should catheterised patients with a positive dipstick but no symptoms be managed?

Do not treat asymptomatic bacteriuria in catheterised patients; treat only if symptomatic; if symptomatic, use first-line per local guidelines and remove the catheter.

What are the typical durations of antibiotic treatment for LUTIs by patient type?

Men: 7 days; non-pregnant women: 3 days (unless complicated); pregnant women: 7 days.

What are the basic steps in treating UTIs according to the notes?

Consult local empiric guidelines; consider likely source; choose first-line treatment if appropriate; adjust based on MC&S results; monitor; review treatment as results become available.

What is the role of MC&S in UTI management?

Confirm the pathogenic organism, identify its species, and determine antibiotic sensitivities to guide treatment.