MSE-3014 L3.5 UTI


Infections of the Urinary Tract

Definitions

  • Urinary Tract Infection (UTI): A condition characterized by the establishment and multiplication of microorganisms in the urinary tract, which includes the bladder, prostate, ureters, or kidneys.

  • Bacteriuria: The presence of bacteria in voided urine.

  • Significant Bacteriuria (Kass, 1956): Defined as the presence of 100,000 bacteria per milliliter of clean catch midstream urine (MSU) (found in its way into the bladder)

  • Low Count Bacteriuria: Often referred to as urethral syndrome, characterized by lower bacterial counts in the urine. Can be natural in some people such as older people, they may present with some symptoms but can become over-treated

Anatomy of the Urinary System
Pathogenesis of UTIs

  • Mechanisms of Infection:

    • Faecal organisms ascend the urethra

  • Facilitating Factors:

    • Instrumentation of the urinary tract e.g. catheters

    • Sexual intercourse

  • Defensive Mechanisms:

    • Hydrodynamic factors that facilitate the flow of urine - when urine is passed, urethra is flushed out and clean

    • Phagocytosis by immune cells - if immunosuppressed, WBC count may not be sufficient, may not react and makes pt more susceptible to UTI

    • Humoral immunity involving antibodies

    • Non-specific antibacterial substances found in secretions from the prostate and mucosal glands

Predisposing Factors for UTIs

  • Age: Increased susceptibility in both young children and elderly.

  • Sex: Females are more predisposed due to anatomical differences - urethra is shorter and closer to anus

  • Structural/Functional Urinary Tract Abnormalities: Such anomalies can increase the risk of UTIs.

    • Some born with ureters further down mean that urine can sometimes flow back into the kidneys, causing more infections

  • Diabetes Mellitus (DM): Alters immune response and urinary tract function - higher blood glucose in bloodstream gives bacteria more nutrients

  • Immunosuppression: Reduced immune function can lead to higher susceptibility to infections.

Complications of UTIs

  • Pyelonephritis - pus in nephrons, inflammation can lead to…

  • Renal Scarring - existing damage makes someone more susceptible to more damage

  • Septicemia - serious bloodstream infection that can occur from urinary tract infections, or pathogens from urine travel to the blood

    • 80% of UTIs caused by E-coli - produces endotoxins, Lipid A as a by-product

    • Endotoxins lead to disseminated intravascular coagulation, affecting clotting factors etc.

  • Recurrence of UTIs: Individuals may experience multiple infections after initial treatment - increases use of antibiotics > leads to resistance > can cause death

Microbiology of Common UTI Pathogens

  • Escherichia coli (E. coli) : The most common pathogen in UTIs (80%)

  • Enterococcus species: Gram-positive bacteria that can cause UTIs.

  • Staphylococcus saprophyticus: Primarily affects young sexually active females + pregnant people, can cause pre-mature labour

  • Proteus species: Produces alkali, may cause bladder stone formation (treatment no matter what)

  • Klebsiella species: From gut

  • Pseudomonas aeruginosa: From environment, e.g. some patients may have plastic catheters that Pseudomonas and biofilms like to stick to

  • Candida species: Recurring infections can lead to disruption of normal flora

Diagnosis of UTIs
Diagnosis (1) Specimen Collection

  • Types of Specimens:

    • Midstream urine sample (MSU) recommended for best accuracy - collected middle portion of excreting urine, avoiding initial start as it is flushing out organisms, and avoiding the end due to possible debris

    • Catheterized urine sample may also be utilized however chances of organisms proliferating in bag are high and may lead to false positives + WBC count may be important to confirm infection, so sample must be taken from portal before it goes into the bag

    • Clean catch method is preferred to minimize contamination.

    • Bag collections may be used in infants and children.

    • Suprapubic aspirate is another method for specimen collection, often used in more complicated cases - patients who have difficulty passing e.g. male patients with enlarged prostates, blocks everything, so a needle can be put into the suprabpubic area and aspirate it there.

Diagnosis (2) Specimen Transport

  • Necessary to maintain the integrity of urine specimens during transportation:

    • Refrigeration at 4°C: Important to prevent bacterial overgrowth before testing.

    • Dip-slide technique: For on-site culture and identification in certain settings.

    • Boric acid at 1.8%: A preservative used for specimen collection for up to 48 hours, prevents organisms from multiplying further

Diagnosis (3) Testing Methods

  • Dipstick Testing:

    • A method that provides quick results regarding the presence of nitrites, leukocyte esterase, and other indicators. (proteins, haemolysis, glucose)

    • Indications = sample is sent to the lab

  • Microscopy Examination:

    • Evaluation of white blood cells (WBC), red blood cells (RBC), epithelial cells, bacteria, and casts within urine.

    • Crystals, parasites and other cells are visible

  • Semi-quantitative Culture:

    • Involves assessing urine culture results through filter paper or standard loop for quantitative analysis.

    • Semi-automation can streamline this process.

    • Cell count

Diagnosis (4) Significant Bacteriuria

  • Defined as having greater than 10510^5 organisms per milliliter of urine.

  • Usually characterized by pure growth of a single species of bacteria - if patient is catheterised, more may be present

  • The presence of symptoms and pyuria increases confidence in diagnosis:

    • Positive Predictive Values:

    • 80% when symptoms are present and bacteriuria is consistent.

    • 95% confidence when two specimens yield the same organism, but samples must be taken at two different times of the day

Diagnosis (3) Plates

  • Chromogenic Plates

    • Helps identify and quantity of organisms quickly

    • More difficult to see on blood agars

  • Maconkey plates

    • can show lactose fermenters (pink) - uses carbon as a source rather than glucose

  • Quantitative urine culture

    • filter paper is bent and dipped into urine and then pressed into plates to help see how many are present

  • Antibiotic Sensitivity Tests

    • Implemented to determine which antibiotics will effectively treat the bacterial infection.

  •     Relay the effectiveness of various antibiotics against the identified bacteria.

Treatment of UTIs

  • Encouragement of Fluids:

    • Increased fluid intake helps flush out bacteria from the urinary tract.

  • Antibiotics:

    • Specific selection of antibiotics based on culture and sensitivity results.

    • Nitrofurantoin or amoxicillin

    • Duration of Treatment: Tailored to the severity and recurrence of the infection, usually around 5-7 days

    • Test of Cure: Repeat testing may be necessary to ensure the infection has resolved.

    • Prophylaxis: Preventative measures may be recommended, especially for recurrent infections - may induce antibiotic resistance