Study sheet: Urinary Tract Infections

📋 Course Outline

1. Epidemiology and Causative Bacteria
2. Pathophysiology and Natural Defenses
3. Risk Factors and Complications
4. Clinical Forms and Symptoms
5. Urine Testing and Diagnosis
6. Antibiotic Treatment
7. Asymptomatic Bacteriuria
8. Nosocomial Infections and Prevention

📖 1. Epidemiology and Causative Bacteria

★ Must-know

• Urinary tract infections are the second most frequent site of community-acquired infections.

• Urinary tract infections are more frequent in women, with peaks at the beginning of sexual activity and after menopause, whereas they occur mainly in men after age 50 because of benign prostatic hyperplasia.

• The main causative bacteria are:

  • Escherichia coli in 60–80% of cases
  • Staphylococcus saprophyticus in 5–10%
  • Proteus in 5–10%
  • other Enterobacteriaceae
  • enterococci

Further detail

• In children, a urinary tract infection often indicates a malformation of the urogenital tract.

📖 2. Pathophysiology and Natural Defenses

📝 Essential Points

• The urinary tract is normally sterile except for the distal urethra, which is colonized by digestive flora.

• 🔄 The usual ascending pathway is:

  1. invasion of the bladder
  2. possible spread to one or both kidneys
  3. possible spread to the prostate

• Natural urinary defenses include: urethral length, frequent urination, continuous ureteral urine flow, regular bladder emptying, acidic urine, antibacterial urinary proteins, the antibacterial effect of prostatic secretions

💡 Memory Hook

Ascending colonization → bladder invasion → possible kidney or prostate involvement

📖 3. Risk Factors and Complications

★ Must-know

• Risk factors include: a short urethra–anus distance in women, vaginal flora changes caused by antibiotics, spermicides, diaphragms, or menopause, urinary tract abnormalities, urinary retention, diabetes, pregnancy, foreign bodies such as catheters, stones

• Risk factors for complications include any urinary tract abnormality, male sex, pregnancy, frailty in older adults, creatinine clearance below 30 mL/min, and severe immunosuppression.

• Severe sepsis with a Quick SOFA score above 2, septic shock, and a urological procedure other than simple catheterization are severity criteria.

Further detail

• Risk factors for extended-spectrum beta-lactamase-producing bacteria include: previous colonization or infection within 6 months, recent amoxicillin–clavulanate, second- or third-generation cephalosporin or fluoroquinolone use within 6 months, travel to an endemic area, hospitalization within 3 months, long-term institutional living

📖 4. Clinical Forms and Symptoms

🔑 Key Concepts & Definitions

• Simple acute cystitis : a lower urinary tract infection in a woman, including a woman over 65 in good general health without comorbidity, with urinary symptoms but no fever or flank pain
• Cystitis with complication risk : associated with urinary tract abnormalities, comorbidities, male sex, pregnancy, or advanced physiological age with comorbidities

★ Must-know

• Factors promoting recurrent cystitis include:

  • sexual intercourse
  • insufficient fluid intake
  • infrequent urination
  • constipation
  • prolapse
  • post-void bladder residue

• Pyelonephritis usually begins abruptly with unilateral flank pain, fever, chills, and pain on lumbar percussion, and may be complicated by bacteremia, septic shock, or renal abscess.

• Typical urinary symptoms include:

  • frequent small-volume urination
  • painful urination
  • cloudy or bloody urine
  • dysuria or incontinence
  • acute retention
  • lumbar, pelvic, or testicular pain

Further detail

• Prostatitis or orchiepididymitis combines lower urinary symptoms with fever and chills, pelvic pain or heaviness, possible acute urinary retention, possible orchitis, and prostate tenderness on rectal examination.

💡 Memory Hook

Cystitis affects the bladder, pyelonephritis the kidney, and prostatitis the prostate

📖 5. Urine Testing and Diagnosis

★ Must-know

• The urine dipstick is the first-line examination and detects leukocytes, which reflect the inflammatory response, and nitrites, which are produced only by Enterobacteriaceae.

• The urine dipstick has 97% sensitivity and 33% specificity, and its negative predictive value is good in patients without catheters.

• For urine culture, collect the sample before antibiotics after hand washing and perineal or urethral cleansing, preferably at least 4 hours after the previous urination, by discarding the first 20 mL and collecting the next 20–30 mL in a sterile container.

📐 Formula — Urinary infection is supported by leukocyturia greater than $10/mm^3$ or $10^4/ml$ and bacteriuria greater than $10^4$ colony-forming units per milliliter, depending on sex and organism.

Further detail

• For a urine dipstick, collect the second urine stream in a clean, dry, nonsterile container and read the test after 1–2 minutes according to the instructions.

💡 Memory Hook

Dipstick first, then culture, antibiogram, and imaging when parenchymal involvement is suspected

📖 6. Antibiotic Treatment

📝 Essential Points

• For simple acute cystitis, first-line treatment is single-dose fosfomycin-trometamol and second-line treatment is pivmecillinam; urine culture is not recommended unless treatment fails.

• For cystitis with complication risk, treatment should preferably await the antibiogram; if this is impossible, nitrofurantoin is first-line and fosfomycin-trometamol is second-line.

• Simple acute pyelonephritis is treated with a parenteral third-generation cephalosporin or a fluoroquinolone, with an aminoglycoside as an alternative in case of contraindication.

• Severe pyelonephritis requires hospital treatment and dual therapy combining a third-generation cephalosporin or fluoroquinolone with an aminoglycoside.

• Probabilistic antibiotic treatment must always be adapted to the antibiogram result.

📖 7. Asymptomatic Bacteriuria

🔑 Key Concepts & Definitions

• Asymptomatic bacteriuria : the presence of bacteria in urine without symptoms, occurring in 10% of men and 20% of women over 65

★ Must-know

📌 Asymptomatic bacteriuria should be treated with antibiotics only in pregnant women; treatment is not recommended in other situations.

Further detail

• Asymptomatic bacteriuria becomes more frequent with age and is especially common in institutionalized, bedridden, or catheterized patients.

💡 Memory Hook

Bacteria without symptoms are usually not treated, unlike symptomatic urinary infection

📖 8. Nosocomial Infections and Prevention

★ Must-know

• Nosocomial urinary tract infections account for 40% of nosocomial infections and are mainly associated with bladder catheterization.

• Approximately 30% of urinary catheters are colonized by bacteria on day 3 and 100% are colonized by day 30.

• Catheter prevention requires: limiting catheter indications, reassessing the indication daily, removing the catheter as soon as possible, preferring intermittent catheterization when feasible

📌 For a catheter-associated urinary infection, the catheter should be removed if possible or changed if it has been in place for at least 14 days, and antibiotic treatment should follow the infection type and susceptibility results.

Further detail

📌 Contact precautions are required when a catheter-associated urinary infection involves multidrug-resistant bacteria.

💡 Memory Hook

Urinary catheterization → bacterial colonization → multidrug-resistant nosocomial infection

📊 Synthesis Tables

Main urinary infection forms

Form	Defining features	Main risks or complications
Simple acute cystitis	Lower urinary symptoms without fever or flank pain in a woman without relevant comorbidity	Usually uncomplicated
Cystitis with complication risk	Urinary tract abnormality, comorbidity, male sex, pregnancy, or advanced age with comorbidity	Requires risk-adapted management
Pyelonephritis	Flank pain, fever, chills, and lumbar percussion pain	Bacteremia, septic shock, renal abscess
Prostatitis or orchiepididymitis	Lower urinary symptoms with fever, pelvic pain, retention, and possible orchitis	Prostatic involvement and acute retention