Download UG Clinical

Microbiology: Clinical Aspects of Urinary Tract Infections (Brown)
DEFINITIONS:

Significant Bacteriuria: >105 cfu/mL of urine (only needs to be 102 cfu/mL in symptomatic patients)

Asymptomatic Bacteriuria: significant bacteriuria in the absence of any symptoms suggestive of UTI

Cystitis (Lower UTI): infection confined to superficial bladder mucosa

Pyelonephritis: infection that involves the renal parnenchyma

Uncomplicated UTI: cystits or pyelonephritis that occurs in an otherwise healthy, non-pregnant woman with no
underlying structure or functional abnormality of the urinary tract

Complicated UTI: associated with any of the following
o Obstruction: of any site of the urinary tract (enlarged prostate, uterine/bladder prolapsed, stones, tumor)
o Foreign body: catheter or stent
o Incomplete voiding: detrusor muscle dysfunction (neurologic disease, medications)
o Vesicoureteral reflex: urine travels up the ureters instead of out the urethra (usually only in kids)
o Recent history of instrumentation/invasive urologic procedure
o Renal transplant recipient: always classified as complicated
o Male: always classify as potentially complicated
o Pregancy: always classified as complicated
o Diabetes
o Immunocompromise
o Health-care associated infection
o Multi-drug resistant infection

Recurrence: relapse or reinfection (most often)
o Relapse: recurrence due to the same microorganism (not completely eradicated; within 2 weeks)
o Reinfection: recurrence due to a different microorganism (usually after 2 weeks)
EPIDEMIOLOGY:
Extremely common:
o Second most common CA infection
o Most common health care associated infection (CMS no longer reimburses hospitals for costs due to UTIs
because they are seen as preventable)
Can cause bacteremia: most common source of Gram negative bacteremia
Can cause chronic renal failure: early childhood UTIs
Prevalence by Age Group:
o Infant: more common in males than females, although rare in general
o 1-15 years: more common in females (4-5%)
o 16-35 years: more common in females (increases to 20%- sexual activity)
o 36-65 years: more common in females, but males also increase (due to benign prostatic hypertrophy)
o 65+ years: still more common in females, but very high rates in both genders (again, mainly due to BPH)
Natural History of UTI:
o Bacteriuria in school children = population at greater risk for bacteriuria in adulthood
o Asymptomatic bacteriuria occurs in some pregnancies and many of those will develop pyelonephritis during
pregnancy if untreated
o Symptomatic and asymptomatic UTIs will resolve without treatment, but antimicrobial therapy increases
probability of cure and speeds symptom resolution
PATHOGENESIS:
Bacteria originating in intestine normally colonize vaginal introitus, periurethra and distal urethral meatus
Infection occurs by ascending route:
o This is why it is more common in women (shorter urethra); in addition, prostatic antibacterial secretions
may also contribute to decreased incidence in men
o Sexual intercourse facilitates entry of organisms into the bladder (dose-response relationship between
frequency of intercourse and risk of UTI)
Host Defenses:
o Urine characteristics (high osmolality, low pH, presence of organic acids)
o Flushing out of bladder urine during voiding
o Inhibitors of bacterial adherence to uroepithelial cells (Tamm-Horsfall protein, bladder MPS, sIgA)
o Role of humoral immunity poorly understood
Once established in bladder, can ascend to kidney: kidney can also be infected via hematogenous route (rare)
CLINICAL PRESENTATION:

Cystitis:
Mild infection:
o Dysuria, urgency, frequency, possible hematuria
o Suprapubic or low back pain
o NO signs of systemic infection (fever, chills etc.)
Physical Exam: suprapubic tenderness
Differential: perhaps vaginitis or urethrisis, but the urgency and frequency are pretty characteristic of cystitis

Pyelonephritis:
Symptoms:
o Symptoms of cystitis may or may not be present
o May have flank pain/tenderness
o Signs of systemic toxicity present: fevers, chills, N/V/D, hypotension
Physical Exam: fever and costovertebral angle tenderness
Presentation in the elderly is a diagnosis of exclusion: presence of bacteriuria high in elderly to begin with; need to
thoroughly asses and may present as one of the following
o Unexplained fever
o New onset incontinence
o Change in mental status

UTIs in Pediatric Population:
Infants: non-specific presentation
o Poor feeding
o Failure to gain weight
o GI symptoms
o Unexplained fever (including febrile seizures)
Toddlers/Preschoolers:
o Lower tract symptoms
o Recurrence of daytime/nocturnal enuresis
o Fever
School-Aged: same as adults
EVALUATION:

Urine specimen required:
Midstream “clean catch”
Stick on bags for infants and toddlers
Catheterization may be used to obtain specimen

Once obtained:
Dipstick: to detect presence of RBCs, WBCs and bacteria
o WBCs in urine (pyuria) is supportive of UTI
Patients with Pyuria:
o Spin Specimen: 5-10 leukocytes per high-power field considered significant
Before Knowing Presence of Pyruria:
o Gram Stain of Unspun Specimen: 1 or more bacteria per high-power field considered significant

Represents growth of greater than 105 cfu/mL in urine culture

Easy way to detect pyuria, bacteriuria and morphology of infecting agent all at once

Managing Uncomplicated Cystitis:
o Treat empirically: healthy, non-pregnant woman who presents with classic signs of cystitis
o Culture of urine is not recommended: results would not be available in clinically meaningful time frame

Microbiology is predictable

May use urine dipstick to confirm diagnostic impression

Treatment of Complicated Cystitis and Pyelonephritis: requires urine culture

Differentiating Lower UTIs (Cystitis) from Upper UTIs (Pyelonephritis):
o Usually based on clinical grounds:

Issue is that ~30% of women with symptoms of cystitis may have subclinical pyelonephritis

Laboratory tests attempt to localize infection more accurately
 WBC Casts: specific for pyelonephritis (ie. if present, its pyelonephritis) but not sensitive
because they are not present in all cases of pyelonephritis

Smell and appearance of urine is not evidence of a UTI: rather, evidence of hydration and recent dietary intake
MICROBIOLOGY:

Cystitis:
E.coli: 80%
S.saprophyticus: 10-20%
Rarely: Proteus, Klebsiella, Enterococcus

Pyelonephritis:
E.coli: mainly
Klebsiella, Proteus
Rarely: coagulase-negative staph (epidermidis, albus)

Complicated Infections and Healthy Care-Associated UTIs:
E.coli: still an important cause
Others: Proteus, Klebsiella, Enterobacter, Serratia, Citrobacter, Pseudomonas, Enterococcus

Pediatric Population:
E.coli: mainly
Klebsiella, Proteus
Rarely: coagulase-negative staph (epidermidis, albus)
MANAGEMENT:
No questions from this lecture on this*
Important Points:
o Asymptomatic Bacteriuria: only treated in certain circumstances

Pregnancy

Prior to invasive instrumentation of urinary tract or urologic surgery

Renal transplant patient (during first 6 months post-transplant)
o Imaging:

Reserved for only some patients:
 Complicated infections
 Recurrent pyelonephritis
 Pyelonephritis that does not respond to appropriate antibiotic therapy (in 72-96 hours)

CAT scans, ultrasounds, and specialized procedures in children looking for vesicoureteral reflux