Microbiology - UTI Flashcards
is the urethra sterile? what about bladder?
- urethra is not sterile
- urine in bladder is sterile but urine coming out urethra is not sterile
what happens id squamous epithelial cells are found in MSU sample?
sample hasn’t been taken properly
define bacteriuria
presence of bacteria in urine
Is asymptomatic bacteriuria relevant?
not usually relevant
but asymptomatic bacteriuria with coliform is significant in PREGNANCY
define cystitis
inflammation of bladder
often caused by infection
AKA: LOWER UTI
what is an uncomplicated cystitis?
infection in a structurally and neurologically normal urinary tract
what is an uncomplicated cystitis?
infection with functional or structural abnormalities e.g. indwelling catheters and calculi
in which groups of patients is the UTI classed as complicated?
- men
- pregnant women
- children (not young girls)
- patients in a HC associated settings
what are most UTIs caused by?
- over 95% of UTIs are caused by single bacterial species
- most common: E.coli
- E.coli have adherence factors that allow it to prevent being flushed out by passage of urine
what is the 2nd most common cause of UTI in young women?
Staphylococcus saprophyticus (coagulase -ve) has virulence factor (P-fimbriae) that allow adherence to epithelium
which bacteria causes UTIs in presence of prosthesis? (e.g. procedures/ long term indwelling catheter)
staphylococcus epidermis
what other organisms can cause UTIs?
- proteus mirabilis
- klebsiella aerogenes
- enterococcus faecalis
what does recurrent UTIs suggest about the organism?
recurrent UTIs (esp in presence of structural abnormalities) increases chances of infection caused by non E.coli organisms (e.g. proteus, pseudomonas, klebsiella, enterobacter, enterococci, staphylococci)
what antibacterial host defences does the urinary tract have?
- urine (osmolality, pH, organic acids to try to stop some bacteria entering)
- urine flow (movement of urine stop bacteria)
- urinary tract mucosa (bactericidal activity, cytokines)
why are females more susceptible to UTIs?
- female urethra is short and in proximity to vulvar/ perianal areas
- contamination is likely
- organisms that cause UTI colonise vaginal/periurethral area first
- massage of urethra/sexual intercourse can force bacteria into bladder
- once in bladder bacteria can multiply
why can renal tract abnormalities increase susceptibility to infection?
- obstruction inhibits flow of urine
- stasis of urine
what are the mechanical causes of obstruction?
Extrarenal: valves/stenosis/bands, calculi, BPH
Intrarenal: nephrocalcinosis, analgesic nephropathy, uric acid nephropathy, PKD, hypokalaemic nephropathy
causes of neurogenic malfunction that increase susceptibility to infection
- poliomyelitis
- tabes dorsalis
- diabetic neuropathy
- spinal cord injuries
what is the problem with vesicoureteric reflux?
- perpetuate infection by maintaining residual pool of infected urine in bladder after voiding
- reflux can result in scarring of kidneys
how can the haematogenous route affect the kidney?
- kidney frequent site of abscess in pt with S. aureus bacteraemia or endocarditis
- S. aureus normally doesn’t cause UTI
- S. aureus doesn’t have appropriate virulence factors to cause ascending infection
symptoms of UTI in children <2 years (inc. neonates)
symptoms are non specific
- failure to thrive
- vomiting
- fever
symptoms of UTI in children >2 years
localised symptoms
- frequency
- dysuria
- abdominal or flank pain
what are the lower UTI symptoms?
- bacteria = irritation of urethral and vesical mucosa = frequent/painful urination of small amounts of turbid urine
- suprapubic heaviness/pain
- gross haematuria
- fever absent (in infections confined to lower UT)
what are the upper UTI symptoms?
- lower UT symptoms (frequency, urgency, dysuria) = may precede UUTS by 1/2 days
- fever with rigors
- flank pain
what are the symptoms of UTI in older patients?
- asymptomatic (not specific symptoms)
- atypical (e.g. abdo pain, confusion)
- diagnosis difficult as non infected older pts often experience frequency/dysuria/hesistancy and incontinence
investigations of uncomplicated UTI/pyelonephritis
- urine dipstick
- MSU for urine MC&S
- Bloods - FBC, U&E, CRP
what do nitrites in the urine suggest?
E.coli UTI
E. coli produces lots of nitrites
Leucocyte esterase +ve
Nitrite +ve
UTI
Leucocyte esterase -ve
Nitrite +ve
start ABx
further management guided by urine culture
Leucocyte esterase +ve
Nitrite -ve
only start ABx of clinical evidence of UTI
may be caused by non-coliform bacterium
further investigations for complicated UTI
renal USS
IV urography
what should you consider in sexually active young men?
chlamydia trachomatis
in which patients should laboratory testing for MC&S be done?
- pregnancy (asymptomatic bacteriruia issue)
- suspected UTI in children
- suspected UTI in men
- suspected pyelonephritis
- catheterised pt
- failed antibiotic tx (resistance)
- abnormalities in GU tract
- renal impairment
why is a MSU better than first catch urine?
- more representative of what is going on in bladder
- first catch may be contaminated by urethral bacteria that is not part of disease process
what is the problem with giving unnecessary antibiotics?
- killing normal bacteria may result in thrush
- yeasts not affected by Abx
which urine culture results are diagnostic of a UTI?
- culture of single organisms >10^5 CFUs/mL + urinary symptoms
- culture of E.coli or S.saprophyticus >10^3 CFUs/mL + urinary symptoms
how do you interpret white cells in urine culture?
WBCs >10^4/mL = inflammation
pyuria is usually absent in childre
what can contaminate a urine culture?
- mixed growth reduces significance of urine culture (suggests contamination)
- epithelial cells present in high numbers = failed MSU technique
if there is a sterile pyuria (raised WCC but no growth on culture) what could it be?
- prior treatment with antibiotics (most common)
- catheterisation
- TB
- Calculi
- bladder neoplasm
- STI (Chlamydia)
what are the different lab testing techniques?
- microscopy
- culture (chromogenic agar - turns different colours based on growth)
- sensitivities
what different colours does chromogenic agar go?
- Pink = E. coli
- Blue = other coliforms
- Light blue = gram +ve
what sampling techniques are used?
- MSU (best method)
- Catheterisation ( may introduce organisms)
- Suprapubic aspiration (very young children)
what are the most common antibiotics used for uncomplicated UTIs?
- trimethoprim
- nitrofurantoin (not in pregnancy as associated with haemolysis)
- cephalexin
how long is treatment given for?
- 3 das of therapy for uncomplicated UTI in women
- women with previous UTI caused by antibiotic resistant organisms or > 7 days symptoms and in men give 7 days of tx
which patients are affected by candida UTIs?
pts with indwelling catheters
management of candida UTIs?
- removal of catheter
- antifungals no more effective than no therapy
- no benefit in treating asymptomatic infection
when should you treat asymptomatic candida UTIs?
- renal transplant patients
- pts who are waiting to undergo elective urinary tract surgery
define pyelonephritis
infection of kidney
what is the link between organism number and infection of parts of kidney?
- few organisms needed to infect renal medulla
- many needed to infect cortex
management of pyelonephritis
- prior to culture results = amoxicillin (or ciprofloxacin)
- culture results = co-amox, gentamicin
when do you do imaging in men/women?
men = calculi women = structural cause
complications of pyelonephritis?
- perinephric abscess
- chronic pyelonephritis (scarring, chronic renal impairment)
- septic shock
- acute papillary necrosis
