Pathology of Urinary Tract Infection Flashcards
what is the typical presentation of a UTI?
- Dysuria (pain on micturition)
- Frequency
- Smelly urine
But:
- very young – unwell, failure to thrive
- very old – incontinence, off their feet
How much renal blood flow is there?
Renal blood flow = 20 to 25 % cardiac output
how does urine output change with fluid intake?
Resorption of fluid is diminished if increase fluid intake = increased urine output
do ureters store urine?
Ureters have continuous trickle of urine – they do not store urine
how do the ureters enter the bladder?
Ureters enter bladder at angle
why does the ureter enter the bladder at an angle?
Increasing pressure from bladder, as it fills, closes off ureter and stops reflux of urine
1 way, continuous flow of urine
what are the bacteriostatic properties of the normal urinary tract?
- Free flow of urine through normal anatomy - assumes drinking enough fluids
- Low pH, high osmolality, and high ammonia (NH3) content of normal urine
- prostatic secretions are bacteriostatic
- anti-bacterial antibodies
is the normal urinary tract sterile?
Urinary tract, except for terminal urethra, is sterile
are urinated specimens sterile?
Initial voiding will _____ ___ many terminal urethral floral bacteria
flush out
how do you take a urine specimen for culture?
intial urine is heavily contaminated, collect after initial void
Patient voids and stops mid-stream, discarding urine, then collects next volume of urine = MSSU (mid-stream specimen of urine)
In a Mid Stream Specimen Urine, MSSU, ar ethere any bacteria?
urethral flora diminshed but always present
what do you do with the MSSU
culture it
Got a problem on how to interoperate it as always a few bacterial colonies
urethral flora will always grow in culture
how to tell contamination from real infectionwhen culturing a MSSU?
- MSSU - microbiology for culture under set conditions
- Bacteria multiply in log phase growth
what levels usually indicate an infection?
105 usually = infection
105 per ml - <1:100 chance of contamination if asymptomatic – ie 99 times out of 100, 105 bacteria per ml represents infection – if specimen = MSSU
what does 103 - 104 indicate?
infection sometimes
probable infection if have symptoms
50% chance of infection if no symptoms
What does <103 represent on a MSSU culture?
usually no infection
MSSU are more difficult to collect in what people?
Difficult to collect in young children and elderly
what are problems with interpritation of urine cultures?
Some bacterial species are not normally present in terminal urethra/rectal flora and may be pathogenic at low colony numbers
What micro-organisms cause UTI?
- Bacteria mostly = gut flora, especially E.coli
- Viral infection rare
what is the route of infection?
always ascending?
how does an infection in the kidneys come about anf what is it classed as?
- Infection in kidneys: usually infection has spread up from bladder infection
- Upper urinary tract infection = more serious
infection of urethra is called?
urethritis
infection of bladder is called?
cystitis
infection of ureter is called?
ureteritis
infection of the kidney is called?
acute pyelonephritis
if recurrent/prolonged infection = chronic pyelonephritis
whata re predisposing factors of UTI?
a. Stasis of urine
b. Pushing bacteria up urethra from below
c. Generalised predisposition to infection
what are the 2 things that may cause stasis of urine?
- Obstruction, whether congenital (presents in childhood) or acquired (adults)
- Loss of ‘feeling’ (sensory loss) of full bladder - spinal cord/brain injury
What things may push bacteria up urethra from below?
- Sexual activity in females
- Catheterisation (and other urological procedures)
what is an examples of generalised predisposition to infection?
Eg. Diabetes
stasis urine:
Bacteria that do get higher up do not get ______ out
flushed
what happens if there is an obstruction at the level of the urethra?
Upper urethral and bladder dilatation
Bilateral hydroureter (dilation of ureter)
Bladder dilatation, bilateral hydroureter and bilateral hydronephrosis (kidney swells due to urine failing to properly drain from the kidney to the bladder) - chronic renal failure
What happens if there is an obstruction at level of renal pelvis on 1 side only?
Unilateral hydroureter
Unilateral hydroureter and unilateral hydronephrosis
what are the consequences of obstruction?
- Proximal dilatation
- Slowed urine flow - Cannot flush out bacteria - infection
- Slowed urine flow - sediments form - calculous (stone) formation - obstruction
obstruction leads to more dilation, increased calculous formation and more infections
• Some bacterial infections predispose to calculous formation
causes the triad seen below:
obstruction in children can be due to what?
Numerous renal tract abnormalities
when should you investigate obstruction in children?
• Always investigate at 1st presentation and send to paediatric surgeons
what is an important example of obstruction in children?
vesicoureteric reflux
what is vesicoureteric reflux
decreased angulation
a condition in which urine flows backward from the bladder into the ureters/kidneys
what does vesicoureteric reflux cause?
backflow of urine
hydroureter - dilation of the ureter
much worse if it is bilateral but usually unilateral
what are the common causes of obstruction in adults?
- Men – Benign Prostatic Hyperplasia (not a tumour) of prostate – functional and anatomical obstruction
- Women – uterine prolapse
- Both sexes – tumours and calculi
what may be the cause of loss of ‘feeling’ of full bladder
spinal cord/brain injury
picture showing the normal emptying of the bladder
Get rid of any bacteria that happen to of come up the urethra
how does decreased sensation due to spinal cord/brain injury affect the emptying of the bladder?
Decreased sensation - no sense of when to micturate and do not know to empty bladder completely - leave urine in bladder (high residual volume) - stasis of urine
Pushing bacteria up urethra from below may be caused by what?
- Sexual activity and female
- Catheterisation (and other urological procedures)
Sexual activity and female is typically dependent on what?
age dependent
Hypothetical graph of urinary tract infection incidence with age
In children due to things like Vesicoureteric reflux infection
How does sexual activity in females cause UTI
In females sexual activity tends to move lower urethral flora up the tract (back wall of urethra is just in front of vagina)
why is the femal sex predispositioned to UTI?
- 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 Catheterisation (and other urological procedures) cause UTI?
Any instrumentation of urinary tract tends to move lower urethral flora up the tract
An examples of generalised predisposition to infection is diabetes, how does diabetes cause a UTI?
- Glucose in urine
- Poor function of WBC
summary of various predisposing factors causing a UTI
what are Acute complication of UTI?
• Severe sepsis and septic shock
what are chronic complications of UTI?
- Chronic damage to kidneys if repeated infections (chronic pyelonephritis) - hypertension, chronic renal failure
- Calculi - obstruction - Hydronephrosis - hypertension, chronic renal failure
what is the key question to think about with a UTI?
Why has this patient presented now?
