Urinary Tract Infections Overview

Urinary Tract Infections (UTIs)

• UTIs are common bacterial infections, particularly in females. Recurrent infections are common, especially in women.
• UTIs are less common in men, typically occurring after age 50.
• UTIs can range from acute and short-lived to contributing to significant morbidity. Severe infections can lead to kidney damage. -Most infections are acute and short-lived, but UTIs contribute to a significant amount of morbidity

Definitions

• Lower UTI: Infection of the bladder (cystitis).
• Upper UTI: Infection of the ureters and kidneys (pyelonephritis).
• Recurrent UTI: Relapse or re-infection. Clinically significant number depends on age and sex (e.g., ≥2 infections in 6 months or ≥3 infections in 1 year).
• Uncomplicated UTI: Infection in a structurally and neurologically normal urinary tract of premenopausal, non-pregnant women without relevant abnormalities or comorbidities.
• Complicated UTI: Infection in the presence of factors predisposing to persistent or relapsing infection. These factors include: males (treatment for minimum 7 days), pregnant females, postmenopausal females, children, diabetes, foreign bodies (e.g., stones, catheters), obstruction, immunosuppression, renal failure, renal transplant, urinary retention (neurological), and anatomical abnormalities.

Asymptomatic Bacteriuria

• Presence of bacteria in the urine without symptoms.
• Often has no adverse consequences and doesn't require antibiotic treatment.

How UTIs Occur

• Urine is normally sterile.
• Bacteria ascend from the urethra to the bladder.
• Natural defenses include: elimination in the urethra, pH, chemical content, flushing, and urine inhibiting some bacteria (e.g., non-haemolytic streptococci, corynebacteria & staphylococci) but can be a good medium for Gram negative bacteria.

Pathogenesis: Mechanical Host Factors

• Disruption of urine flow (e.g., strictures, incomplete bladder emptying, pregnancy, prostatic hypertrophy).
• Renal calculi.
• Tumors.
• Facilitation of bacterial access to the bladder (e.g., sexual intercourse, catheterisation).

Pathogenesis: Other Host Factors

• Hormonal changes (e.g., pregnancy and progesterone).
• Immunological factors.
• Behavioral factors (e.g., urinary irritants, voiding practices).

Causative Organisms (Bacteria)

• Escherichia coli (70-95% of cases).
• Staphylococcus saprophyticus (5-10% of cases).
• Proteus mirabilis (more common in males; associated with renal abnormalities, esp. calculus).
• Klebsiella pneumoniae.

Viral Infections (UTIs)

• Human polyomaviruses (e.g., hemorrhagic cystitis). Enter via the respiratory tract, infect epithelial cells in kidney tubules and ureter.
• Cytomegalovirus and rubella (usually asymptomatic).
• Adenovirus (can cause hemorrhagic cystitis).

Fungal & Parasitic Infections

• Candida spp (rare, but seen in people with risk factors like catheters, immunosuppression or diabetes).
• Histoplasma capsulatum.
• Trichomonas vaginalis (urethritis, often considered vaginitis).
• Schistosoma haematobium (inflamed bladder and hematuria).

Etiology (UTIs)

• Community-acquired UTIs: Primarily E. coli.
• Hospital-acquired UTIs: Gram-negative bacteria (e.g., E. coli, Klebsiella, Enterobacter, Proteus mirabilis, Serratia spp, Pseudomonas aeruginosa), gram-positive bacteria (e.g., Staphylococcus saprophyticus, Staphylococcus epidermidus, Enterococcus spp), and other bacteria (e.g., Salmonella typhi, Staphylococcus aureus, Mycobacterium tuberculosis).

Pathogenicity vs. Virulence

• Pathogenicity: Ability to cause harm.
• Virulence: Severity of harm caused, influenced by virulence factors (ability to evade host defenses).

Virulence Factors

• Adherence: Fimbriae/pili help colonization
• Evasion of Immune System: Capsule and exotoxins/endotoxins.
• Pili, fimbriae, flagella are motility elements that affect adherence and help colonization and evade the host immune system

Etiology (Bacteria - cont'd)

• Escherichia coli: Commonest cause of ascending UTIs (>70%).
• Proteus mirabilis: Associated with kidney stones (produces urease).
  • Urease catalyzes the conversion of urea to ammonia, making urine alkaline, which favors stone formation.

Pathogenesis: Virulence Factors (cont'd)

• Fimbriae (pili): Important colonization factors; certain types (e.g., Type 1, Type 2) target different areas of the urinary tract.
• Capsular acid polysaccharide antigens: Anti-phagocytic.
• Hemolysin: Damages bladder mucosa.
• Urease production (especially in Proteus spp): Correlated with pyelonephritis and kidney stones.
  • Urease catalyzes the conversion of urea to ammonia, making urine alkaline, which favors stone formation.
• Biofilm: Groups of micro-organisms adhere to surfaces, increasing resistance.

Incidence

• Higher incidence in females due to shorter urethra and lack of a prostate.
• Increased incidence in teens due to potential urethral trauma.
• Incidence generally increases with age due to anatomical changes or dysfunction.

Signs and Symptoms (UTIs)

• Kidney (pyelonephritis): Upper back/side pain, high fever (>38°C), shaking chills, nausea, vomiting, malaise.
• Bladder: Pelvic pressure, lower abdomen discomfort, frequent painful urination, blood in urine, dysuria (burning), frequency (sense of having to urinate frequently), urgency, pyuria.
• Urethra: Burning with urination, discharge.

Diagnostic Considerations

• UTIs need consideration in flank/back, pelvic/abdominal pain.
• Exclude other infections (e.g., STDs).
• A urine sample is essential, and positive test results (nitrites, leukocytes, blood, >10x5 CFUs/mL single organism) indicate bacterial infection

Differential Diagnoses

• Infectious Causes of Sterile Pyuria: Perinephric abscess, urethral syndrome, renal tuberculosis, fungal infections.
• Non-Infectious Causes of Sterile Pyuria: Uric acid and hypercalcemic nephropathy, lithium and heavy metal toxicity, sarcoidosis, interstitial cystitis, polycystic kidney disease, genitourinary malignancy, transplant rejection, urethral issues

UTIs in Pregnancy

• Potentially adverse outcomes for mother and fetus.
• Urine cultures are crucial.
• Bacteriuria is treated regardless of symptoms. Cephalosporin is the drug of choice for positive cultures or symptomatic infections.

Differential Diagnoses (Elderly)

• Obstruction (UTIs in elderly can often be complicated by obstruction).
• Acute pyelonephritis, bladder cancer, chlamydial infections, non-bacterial cystitis, herpes simplex, interstitial cystitis, pelvic inflammatory disease, urethritis, vaginitis.

Complicated UTIs in Men

• Less frequent but more common in older men.
• Conditions to consider: prostatitis, epididymitis, cystitis, emphysematous and xanthogranulomatous pyelonephritis, tuberculosis.
  • Consider prostate-specific antigen (PSA) test and digital rectal examination (DRE) for men aged 45+ with lower UTI or visible haematuria. In men aged 60 or older with unexplained non-visible haematuria and either dysuria or high white cell count, bladder cancer needs exclusion.

Concerns Associated with UTIs

• Mechanical Obstructions: Common issue in children and elderly.
• Recurrent Infections: Further investigation warranted.
• Ascending Infections: Pyelonephritis can be life-threatening.
• Pregnancy: Asymptomatic bacteriuria linked to adverse outcomes.
• Missed Diagnosis: Esp. STDs

Risk Factors for Recurrent UTIs

• Frequency of sexual intercourse (esp. young women).
• Atrophic urethritis and vaginitis (postmenopausal women).
• Urinary tract abnormalities (e.g., indwelling catheter, neuropathic bladder, reflux, obstruction).
• Incomplete bladder emptying.
• Exposure to irritants.
• Previous urinary tract surgery.
• Immunocompromised status.

Management Options (Lower UTI)

• Uncomplicated UTI (female): 3 days of nitrofurantoin or trimethoprim (if low resistance risk, or cephalosporin). Amoxicillin unsuitable due to resistance. Quinolones and co-amoxiclav reserved for confirmed resistant cases.
• Symptomatic Treatment: Drink plenty of fluids, avoid alcohol/caffeine/irritants, avoid delaying urination, wipe front-to-back, wash genital area before and after sex and after intercourse, use analgesics (e.g., paracetamol, ibuprofen), and avoid urethral irritants.
• Delayed Rx: Palliative advice (drink fluids, avoid irritants).

Signs & Symptoms – Upper UTI (Pyelonephritis)

• Acute Pyelonephritis: features of lower UTI plus fever (>38.5°C), flank/loin pain/tenderness, rigors, nausea, vomiting, and malaise.

Management/Treatment Considerations - Pyelonephritis

• Causative Agents: E. coli, Enterococcus faecalis, Pseudomas spp.
• Progression: Can lead to perinephric abscess, permanent scarring, chronic pyelonephritis, acute renal hypertension, renal failure, and potentially fatal uremia.
  • In most cases, pyelonephritis, especially in males, results from obstructions like calculi, tumors, or prostatic enlargement.

Key Takeaways

• Understand the different types of UTIs (lower/upper, uncomplicated/complicated).
• Recognize risk factors and symptoms for diagnosis.
• Apply appropriate clinical decision rules for antibiotic use.
• Note the importance of distinguishing "simple" from "complicated" infections, particularly in recurrent infections or infections in specific populations (men, pregnant women).