Urinary Tract Infections

Why UTIs Are So Common

UTIs rank second only to respiratory infections in human infections.

Bacterial Factors Predisposing to UTIs

Several bacterial factors contribute to the prevalence of UTIs:

Capsules

• Capsules are slippery outer layers that certain bacteria possess.
• They provide resistance against phagocytes (white blood cells that engulf bacteria).
• Capsules are antiphagocytic, hindering the ability of phagocytes to ingest the bacteria.

Hemolysis

• Hemolysis refers to the breakdown of red blood cells.
• Bacteria producing hemolysis have increased access to nutrients due to the kidney's role in filtering blood.
• Many UTI-causing E. coli strains are hemolytic.
• Hemolysis can be visually detected as a zone of lysis around E. coli colonies on horse blood agar plates.

Urease Production

• Some bacteria produce urease, an enzyme that breaks down urea.
• This is advantageous in the bladder, which contains a high concentration of urea filtered by the kidneys.

Fimbriae

• Fimbriae are structures that enable bacteria to attach to host cells.
• Uropathogenic E. coli (UPEC) strains exhibit strong adherence to bladder epithelium via fimbriae.
• Fimbriae facilitate bacterial persistence by resisting flushing mechanisms.

Colonization

• Bacteria residing on the body, particularly in the rectum, can cause UTIs.
• These bacteria can ascend to the urinary tract.
• Ascending infections typically begin with bacteria colonizing the perineal skin, often due to improper wiping (back to front instead of front to back) or sexual activity.
• Females are more susceptible due to a shorter urethra, which facilitates bacterial ascension.

Host Factors Predisposing to UTIs

Several host-related factors increase the risk of UTIs:

Renal Calculi (Kidney Stones)

• Kidney stones can act as foreign bodies in the urinary tract.
• Bacteria can adhere to these stones, shielding themselves from the immune system.
• The presence of renal calculi significantly increases the risk of recurrent UTIs.

Descending Infections

• Bloodstream infections can lead to kidney infections via a descending route.
• During severe bloodstream infections, bacteria may access the kidneys through the filtering process.

Ureteric Reflux

• Ureteric reflux occurs when the valve at the junction of the ureter and bladder is faulty, allowing backflow of urine.
• This condition leads to recurrent kidney infections, particularly in children.
• Reflux can occur when lying down or during bladder contraction.
• Surgical correction is often required for this valve issue.

Bladder-Related Factors

Tumors

• Bladder tumors compromise local immunity, making them susceptible to bacterial colonization.
• Tumor-associated bacteria become difficult to eradicate, causing recurrent UTIs.
• Detection of unusual cells in urine samples may indicate a potential tumor, warranting further cytological investigation.

Pregnancy

• Pregnant women are prone to asymptomatic bacteriuria, where bacteria are present without symptoms.
• Due to immune system suppression and pressure from the fetus, reflux can occur.
• Untreated asymptomatic bacteriuria increases the risk of kidney infections; therefore, antenatal urine screening is essential.

Neurogenic Bladder

• Neurogenic bladder, often seen in paraplegics, involves impaired bladder control.
• Self-catheterization, a common necessity, introduces bacteria into the bladder, increasing UTI risk.
• Frequent catheterization often leads to chronic antibiotic treatment.

Incomplete Bladder Emptying

• As women age, bladder prolapse can cause incomplete emptying, leaving residual urine.
• This residual urine acts as a reservoir for bacteria, promoting recurrent infections.

Diabetes

• Diabetic patients are more susceptible to UTIs due to hyperglycemia, which impairs immune function.

Age

• Aging is associated with both bladder dysfunction and weakened immunity, predisposing individuals to UTIs.
• Concurrent dementia complicates UTI management in the elderly, as patients may struggle to communicate their symptoms.
• While antibiotic use in the elderly is approached cautiously, withholding treatment can negatively impact mental well-being.
• Increased antibiotic usage in this demographic contributes to antibiotic resistance.

Catheter Use

• Urinary catheterization introduces bacteria into the bladder, increasing UTI risk.

Prostate-Related Factors

Prostate Hypertrophy

• Prostate hypertrophy in aging men can obstruct bladder drainage.
• This obstruction leads to residual urine and subsequent UTIs.

Urethra-Related Factors

Sexual Intercourse

• Sexual intercourse can propel bacteria into the urethra, increasing UTI risk.
• Historically, UTIs linked to sexual activity were known as honeymoon cystitis.

Vaginal Flora

• Lactobacilli in the vagina of reproductive-age women produce acid, which offers some protection against infections.
• Young children and elderly women have lower estrogen levels and reduced lactobacilli, increasing UTI susceptibility.

Foreskin

• The foreskin can harbor bacteria, and circumcision in boys is associated with a slightly lower UTI risk.