Urinary Tract Infection
AM Nicholson
MB BS; DM (Med Micro)
Knock, Knock, Knock!!
Definition/ Introduction
One of the most commonly encountered
acute infections
Bacteria in the urine
Covers spectrum from asymptomatic
bacteriuria to severe pyelonephritis
May be of lower or upper urinary tract
Urinary Tract
Upper
Kidney
Ureter
Lower
Bladder
Urethra (Genital tract)
Classification
Upper: Pyelonephritis, ureteritis
Lower: cystitis
Uncomplicated, complicated
Acute, chronic, recurrent, relapsing
Community or hospital acquired (HCAI)
Uncomplicated UTI
Uncomplicated UTI: one occurring in a
healthy, ambulatory, non-pregnant female
without any underlying structural
abnormality or neurologic dysfunction.
Mostly due to E coli
More susceptible organisms
Easy to treat
Complicated UTI
UTIs at sites other than the bladder eg
pyelonephritis.
Those in children, most men, pregnant
females.
Those associated with obstruction,
urologic dysfunction, catheters, renal
transplant recipients
High risk groups: immunocompromised,
pregnancy, diabetes, hypertension
Complicated UTIs contd.
Warrants broader spectrum antimicrobial
coverage (MDRO)
Infrequently requires surgery
High incidence of organisms other than
E coli.
Recurrent Infection
Reinfection: new infection with new organisms.
Infection cleared for 2 weeks or more after
treatment. Recurrence of symptoms. Isolation of
new organism or new strain
Relapse: recrudescence of prior, partially
treated infection. Same organism involved.
Occurs shortly after completion of therapy
(days - 1mth)
Epidemiology
In patients < 3 months there is increase in
boys> girls but ratio is reversed after that
More common in females (long urethra
protects males)
Elderly men and women have about
same prevalence
90% caused by part of normal flora
Organisms
Gram negs:
Enterobacteriaceae:
E coli
K pneumoniae, Proteus,
Enterobacter, Serratia.
Pseudomonas spp
Gram pos:
Enterococcus faecalis
Staph saprophyticus (comm.)
Staph epidermidis (hosp)
Staph aureus
Acid fast: M tb
Yeast: C albicans
Parasite: Schistosoma
haematobium
Determinants of Infection
Inoculum size: need large numbers
Virulence: only certain spp. cause upper
UTIs
Urinary tract abnormalities: obstruction,
reflux, catheters
Receptor density in uroepithelial cells
Determinants of Infection contd.
Host defense mechanisms:
complete bladder emptying: one of the most
important defense mechanisms. Urine is
normally sterile but good culture medium so if
high residual volume, bacteria will thrive
High fluid intake & frequent voiding: ? Washout
bacteria
Vesicourethral valve: prevents reflux of bacteria
from bladder
Length of urethra
Vaginal flora eg lactobacillus decreases
colonization with E coli
Virulence
UTI: relies on bacteria to adhere & colonize
gut, perineum, urethra, bladder, kidney
Adhesion is important esp. in normal U/ tract
Pathophysiology of adhesion is complex
Enterobact.: electronegative & too small to
overcome repulsion by the net negative
charge of epithelial cells
Virulence contd.
Bacterial adhesion cannot occur in absence of
fimbriae or other nonfimbrial surface adhesion
systems
Fimbriae allow irreversible attachment to
uroepithelium via adhesins
Adhesins: found on tip of bacterial fimbriae and/ or
on bacterial surface itself (non-fimbrial adhesins)
Specific adhesion systems exist for orgs. Eg P
fimbriae for E coli.
Virulence factors: E coli
Virulence is NOT related to antimicrobial
resistance: most adherent strain sens.
Main serotypes: O1, 2, 4, 6, 7, 16, 18 & 75
Present in 28% of normal faecal flora but
account for 80% of pyelonephritis, 60%
cystitis & 30% asymptomatic bacteriuria
Flagellae:motility
Hemolysin production: induces pore
formation in cell membrane
Virulence factors: E coli contd.
Siderophore: necessary for iron uptake in
the iron-poor environment of the U/tract
K antigen: nonfimbrial adhesin, promotes
strong biofilm growth. Assoc with
persistence in bladder
Virulence is not related to antimicrobial
resistance: most adherent strain:very
sensitive
Pathophysiology/ pathogenesis
Normal urinary tract is sterile except for distal
urethra which may have Gm pos & Gm neg
bacteria.
Ascending infection: The most important
means by which infection occurs (coliforms).
Urethral orgs. spread to bladder
Hematogenous infection: Acute pyelonephritis
secondary to Gm neg bacteremia can occur but
not common.
May lead to descending infection
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Clinical presentation
From asymptomatic bacteriuria to
pyelonephritis
Lower: Cystitis
Include dysuria, urgency, hesistancy,
frequency, incomplete voiding, urinary
incontinence, haematuria (gross or
microscopic) & suprapubic pain
The elderly may present with confusion and
no localizing features
Constitutional symptoms such as fever are
Lower: Urethritis
Females: increased frequency & dysuria,
afebrile, pyuria without bacteriuria, H/O
STI
Males: Dysuria & urethral discharge. H/O
STI
Lower UTI contd.
Urethral Syndrome (Frequency Dysuria
Syndrome):
Clinical presentation: Upper
Acute pyelonephritis
(Infection and inflammation of the renal
parenchyma)
Symptoms of lower UTI may be present:
dysuria, frequency, hesitancy, lower
abdominal pain, urgency, haematuria ,
Symptoms of pyelonephritis: flank pain,
back pain, high fever, rigors, chills,
weakness, anorexia, nausea, vomiting,
diarrhoea, constipation
Clinical Upper contd.
Renal abscesses: Symptoms identical to
pyelonephritis. Suspect in patient with UTI
with fever persisting >48-72 hrs.
Asymptomatic bacteriuria
Isolation of specified amount of bacteria in urine of
pr without symptoms.
2 consecutive specimens with >100,000 orgs/ml
with same organism
Or
1 CSU with 100 orgs/ml
Treat pregnant women, pts doing urologic
procedures.
Do NOT treat non-pregnant females, diabetics,
elderly nursing home residents, pts with spinal
cord injury or indwelling catheters
Clinical contd.
UTI in females
UTI in males
UTI in elderly
UTI I children
UTI in patients with catheters
Laboratory Diagnosis
Specimen types
URINE: Primary specimen
Blood: Secondary specimen
Urine samples:
MSU
CSU
SPA
Neonatal bagged urine
In & out catheter urine
Other: nephrostomy urine, bladder
cystoscopy urine
Specimen Collection
First voided morning urine preferable
Urine more concentrated then: more likely
to recover organisms
MSU: distal urethra may have bacteria
Urine Samples: Too much/ Too little!!
Specimen Collection: How To
Wash hands thoroughly with antibacterial soap and hot water;
dry them with a paper towel. Make sure that the soap does not
contain any substances (lotion, scent, etc) that may interfere
with the urine sample.
Prepare the specimen cup. Use care when opening the cup and
lid, making sure to keep the cup sterile. For example, be sure to
place the lid with the inner part facing up on a surface and do
not put any part of your hands on the inner cup or lid.
Thoroughly clean the genital area with antiseptic cleansing
cloths or antibacterial soap and water. Males should pull the
foreskin of the penis back to assure complete cleansing of the
area. Females should separate and cleanse the folds, or lips, of
the vulva. Care should be used as a female cleanses that
wiping occurs from front to back so that feces do not
contaminate the genital area.
Specimen collection contd.
Begin to urinate. Females should hold the folds of
the vulva apart with one hand so that they do not
interfere with the stream.
Place the collection cup under the stream after
urination has occurred for a few seconds. Two fluid
oz. should be collected, unless otherwise specified
and the cup should be removed even if urination is
still occurring. Care should be used to make sure
that the collection cup does not come into contact
with the genitals or anything other than urine.
Place the lid on the collection cup securely. If the
test is going to occur more than an hour after the
urine is collected, refrigerate the urine.
Transport of Specimens
No transport medium needed.
Get to lab within 1 hour of collection or
refrigerate for up to 24 hours
At room temperature, urine will allow
multiplication of contaminants.
Discard if > 24 hours
Check here
Processing of specimen
Macroscopic: describe if cloudy, red or dark
Microscopic: Gram uncentrifuged urine check
here
leucocytes (Pyuria: >10 wbcs/mm3 )
bacteria
Detection of pyuria & bacteriuria: dipstick
Pyuria: sensitive marker & absence suggests another
diagnosis
Dipstick
Nitrite
Leukocyte esterase
Blood
Proteins
Other
Rapid
Simple
Convenient
Cheaper
Culture & Sens.
Culture
Urine culture is semi-quantitative; need to know
if more than 100,000 organisms per ml of urine.
Sample plated onto Blood agar & MacConkey
agar and incubated at 37C for 24 hours
Traditional Interpretation
Organism/ colony forming unit per ml (cfu/ml)
105 or more
Significant
104 -105
Doubtful significance
< 104
SPA (babies)
Insignificant
Any number significant
Increased nos: improper collection, specimen allowed to
stand at room temp
Newer Interpretation
Women with dysuria & pyuria: 100 cfu/ml
or more of a single predominant
uropathogen is significant
Men with 1,000 cfu/ml or more of above:
significant
Contamination?
MSU: >2 organisms
CSU: >3 organisms
SPA: check here
Quantitative culture
Commensal flora from the periurethral area or
vagina may cause contamination, leading to
false positive results
Infecting and contaminating bacteria are
distinguished by quantifying the number of
organisms growing from the urine
Colony counts of contaminants in voided
specimens are low, while infecting organisms
achieve high concentration
Identification & Susceptibility
Biochemical tests
Antibiotics: Cotrimoxazole
Amoxil, Amoxicillin-clavulanic acid
(Augmentin) (20-25% resistance UHWI),
Quinolones (10% resistance),
Nitrofurantoin, Nalidixic acid
Gentamicin
Ceftriaxone
Other as requested
Kirby Bauer Disc Diffusion Test
E-TEST
Scanned forms with discarded
samples
Scanned Urine C/S report
Robert Sue-Ho
UWI
Robert Sue Ho UWI
Robert Sue Ho UWI
Treatment
Acute uncomplicated cystitis in ,nonpregnant woman
3 day regimen more effective than single
dose regimen but 7 day therapy also:
Cotrimoxazole
Fluoroquinolones
Betalactams
Problem of uropathogens resistant to Bactrim
Treatment
Acute complicated cystitis:
Males, diabetic, symptoms >7 days, age
>65,childhood UTI, recent antimicrobial use
---then 7 days regimens of antibiotic
Acute pyelonephritis:
Blood culture in hospitalized patients,15-20% +ve
Duration of treatment 10- 14 days.
Start parenteral then continue with oral
3 dys after starting, pt afebrile & urine sterile
If therapy fails: treat for 4-6 weeks
Treatment
Treat 1st UTI in males with no GU abnorm.
If 2nd occurs, complete urologic evaluation
Cranberry Juice
Prevents adherence
of uropathogens to
uroepitheliumn
May decrease
frequency
The End
