Pathology of Urinary Tract Infection Flashcards
What are some symptoms of UTI’s?
- Dysuria (pain on micturition)
- Frequency / polyuria
- Foul smell of urine
What are some UTI symptoms that are usually specific to very young people? The elderly?
Very young: unwell, failure to thrive
Elderly: incontinence, falls
In the normal urinary tract the ureters enter the bladder at an angle, how does this affect urine flow?
As the bladder fills up pressure from the urine is exerted on the bladder wall, and it closes off the ureter opening - preventing reflux on urine
(one way flow)
What are some of the bacteriostatic properties of urine? (properties stopping bac reproducing)
- Low pH
- High NH3 (ammonia) content
- High osmolality
- Antibacterial antibodies
Describe the level of sterility in the urinary tract
- Terminal urethra not sterile (as urine exits)
- Rest of urinary tract is sterile
How do you collect a urine sample for culture when infection is suspected? Why?
- Get the patient to void and then stop mid-stream, collect the next volume of urine
- Done because initial void flushes out many terminal bacteria, so sample gives more accurate depiction of the bacteria actually infecting the urinary tract
What is the sample of urine collected for culture called?
MSSU - mid-stream specimen of urine
In what cases will there be bacterial flora in the MSSU?
There will always be bacterial flora to be cultured
- the concentration of bacteria detected is what determines whether there is an infection or not
What are the methods for assessing the MSSU? Brief description?
- Dip slide method (quick way): dip the slide into the urine and incubate at 37 degrees for 24h. Appearance of slide gives approx. [bacteria]
- Formal microbiology culture
What concentration of bacteria in the MSSU culture indicates infection?
- 10^5 bacteria/mL
99% chance of infection even if asymptomatic
What concentration of bacteria in the MSSU culture suggests probable infection?
10^3 - 10^4 bacteria/mL
If symptomatic: probably infection. 50% chance of infection if asymptomatic
What concentration of bacteria in the MSSU culture suggests that there is no infection?
< 10^3 bacteria/mL
Usually suggests no infection
What are some issues with MSSU culture for UTI diagnosis?
- Samples can be difficult to collect in young / elderly
- Some bacterial species are not part of urinary flora and may be pathogenic at low conc.
What micro-organisms are responsible for causing UTI’s?
- Bacteria (gut flora - mostly e. coli)
- Viral infection (rare)
What is the most common route of infection when developing a UTI?
- Almost always ascending, from urethra up to rest of urinary tract
- Infection in kidneys has usually spread from bladder. Upper urinary tract infections are more serious
What does infection in the urinary tract cause in the tissues affected?
Inflammation
- Urethra: urethritis
- Bladder: cystitis
- Ureter: ureteritis
- Kidney: pyelonephritis (acute or chronic)
What are the predisposing factors to UTI’s?
- Stasis of urine
- Pushing bacteria up urethra from below
- Generalized predisposition to infection (eg. diabetes, immunocompromised patients)
What pathologies can cause stasis of urine?
- Obstruction (slowed urine flow, can’t flush out bacteria = infection)
- Loss of feeling of full bladder (brain / SC injury - don’t fully empty bladder, residual bacteria = infection)
Where does obstruction tend to occur in the urinary tract? Consequences of each?
- At level of urethra: causes bilateral hydroureter & bilateral hydronephrosis (swelling of ureters & kidneys)
- At level of renal pelvis on 1 side only: unilateral hydroureter & hydronephrosis
What can obstruction at the level of the ureter lead to?
Renal failure
Due to bilateral hydronephrosis
In addition to risk of infection, what can obstruction of the urinary tract lead to?
Formation of calculi
Slowed urine flow - sediments form - calculous (stone) formation - more obstruction
Some types of urinary tract infections can predispose patients to calculi formation
What is the most common congenital urinary tract abnormality that leads to obstruction and stasis of urine in children? Describe the pathophysiology
- Vesicoureteric reflux
- Decreased angle at which the ureters enter the bladder, meaning increased bladder pressure cannot properly close off the ureter opening, causing back-flow of urine that leads to hydroureter and hydronephrosis
What are some common causes of urinary tract obstruction in adults?
Men: benign prostatic hyperplasia
Women: Uterine prolapse
Both: tumours and calculi
How do neurological deficits that affect feelings of bladder fullness cause urinary tract infection?
- Can’t sense when bladder is full / empty, results in partial emptying of full bladder: retention of some urine
- This stasis of urine means all bacteria are not flushed out, leading to infections
What are the main ways by which bacteria are pushed back up urethra from below?
- Sexual activity in females
- Catheterization
Which groups tend to be most at risk of developing UTIs?
- Females
- The elderly
What are some factors that predispose women to UTIs?
- Short urethra
- Lack of prostatic bacteriostatic secretion
- Closeness of urethral orifice to rectum
- Sexual activity (helps if void after intercourse)
- Pregnancy (pressure on ureters and bladder)
How does catheterization of the urinary tract lead to UTI’s?
Any instrumentation of urinary tract tends to move lower urethral flora up the tract
What is the major acute complication associated with urinary tract infections?
- Severe sepsis and septic shock
What are some chronic complications of urinary tract infections?
- Chronic kidney damage if repeated infections (pyelonephritis): hypertension & chronic renal failure
- Calculi (kidney stones): hypertension & chronic renal failure
