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URINARY TRACT INFECTION
Definition
Infection anywhere between the glomerulus and external os of the urethra
Pyogenic
Non-Pyogenic
↓
Tuberculosis
Fungal
Viral
Terms
•
•
Bacteriuria
Significant bacteriuria
Persisent
•
Upper tract or renal bacteriuria
Cystitis
Pyelonephritis
Bacteriuria
Relapse
Intermittent
Recurrence
Re-infection
Blood
vessels
Micturition
1. Collapse of submucosal ureter due
to increased bladder pressure.
2. Contraction of muscles of superficial
trigone lengths submucosal and
intramucosal ureter – further
narrowing of ureteric orifice.
Ureteric orifice
Seminal vesicle
Paraurethral
glands
Testis and
epididymis
© Dept of Clinical Microbiology 2003
Prostate
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Laboratory Diagnosis
Mid-stream specimen of urine (MSU).
Catheter Specimen of urine (CSU)
Supra-Pubic Aspiration
a)
b)
a)
White Cell Count
Culture
Urine
Storage
White Cell Count
10 leucocytes/mm3 – uncentrifuged
‘Sterile Pyuria’
Tuberculosis, the most important cause but the following are recognised:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
b)
Antibiotic treatment
Adrenocortical steroid treatment
Acute febrile episodes
Cyclophosphamide treatment
Haemodialysis
Pregnancy
Renal transplant rejection
Recent genito-urinary trauma.
Analgesia
Prostatis and cysto-urethritis and inflammation at other neighbouring sites
Culture
‘Loop method’
Dip Slide
© Dept of Clinical Microbiology 2003
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Microbiological Factors
Pathogenesis
Bladder Bacteriuria and Upper Urinary Tract Infection:
In majority of cases, infection occurs by the ascending route. A few organisms may arise
from the haematogenous route – Salmonellosis, Tuberculosis and possibly virus infections.
Infection may predominate in a single site, as in Cystitis (the commonest) or Pyelonephritis.
UTI is usually caused by aerobes, mostly intestinal in origin. They usually enter via the
urethra.
1.
2.
Urinary Pathogens
a)
Bacteria: E. coli. Strains usually responsible for pyelonephritis cluster into a few
O serogroups exhibit mannose resistant haemagglutination, usually possess
adhesions and elaborate alpha haemolysin.
b)
Fungi: Candida albicans. Virulence factors
a)
Bacterial Attachment
b)
Bacterial growth rates in urine
Diagnosis
Normally urine is sterile, but it is a good culture medium in which bacteria multiply rapidly.
Hence with infection the bacterial count in urine usually exceeds 100,000 per ml. Urine
specimens from uninfected patients often contain some contaminants from meatus, etc.
which may multiply at room temperature. Accurate diagnosis depends on:
a)
Avoidance of heavy contamination, by mid-stream method (difficult in infants and
elderly bed-ridden women etc., if in doubt, repeat).
b)
Prompt culture, if delay will be more than 5-6 hours, refrigerate (4°C) until cultured.
Alternatively, use Dip-Slide culture.
The white cell count is usually high in infection, except in ASB (see below).
UTI may be uncomplicated or complicated.
© Dept of Clinical Microbiology 2003
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Mechanical Factors in Urethral Infection
Instrumentation
Surgery
Sexual Intercourse
Mechanical Factors in Infection of Bladder
Inefficient flushing:
Low fluid intake
Low urinary output (heart-renal failure)
Infrequent or incomplete micturition
Poor bladder emptying:
Neuropathic bladder
Bladder diverticulum
Post-micturiction residue
(vesico-ureteric reflux, chronic cystitis)
Obstruction of bladder outlet:
Congenital urethral valves
Urethral stricture
Constipation
Prostatic hypertrophy
Bladder stone
Periurethral inflammation
Introduction of organisms
per urethra:
Direct spread of organisms
from the bowel:
Catheterisation
Instrumentation
Diverticular disease
Appendix abscess
Mechanical Factors Relevant to Upper UTI
Primary vesico-ureteric reflux
Intrarenal reflux
Secondary vesico-ureteric reflux due to:
Obstruction of bladder emptying
Hormonal changes in pregnancy
Inflammation and oedema of the bladder around the ureteric orifices
Surgical diversion of ureters
© Dept of Clinical Microbiology 2003
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Obstruction of the renal pelvis due to:
Ureteric calculus
Periureteric junction obstruction
Staghorn calculus
Post-operative ureteric stricture
Papillary necrosis (diabetes, analgesic nephropathy)
Which Patients Should Have Radiological, etc. Investigations?
1.
2.
3.
4.
5.
First infections in all children.
First and recurrent infections and persistent symptoms in all males.
Recurrent infections in females.
Frank or persistent haematuria.
Suspected renal abscess.
Chronic pyelonephritis leading to renal failure in adults, may start from neglected recurrent
UTI and vesico-ureteric reflux in infants and children.
Some Points About Treatment
Any drug that prevents multiplication of organisms in the urine enables the body defences to
eliminate infection although it may recur, especially in complicated infections. Many
antibiotics are secreted in the urine and these may reach quite high concentrations in the
bladder. I may be necessary to acidify the urine as some antibiotics are more effective at low
pH. It is also important to ensure that the patient has good fluid intake.
For treating uncomplicated infection
Many drugs are available, but several have disadvantages (resistant bacteria, toxicity,
expense etc.). Pending the results of sensitivity tests, favoured ‘first-line’ drugs for acute
infection include trimethoprim, nitrofurantoin, and amoxycillin and amoxycillin/clavulanic acid.
Resistance to some of these agents has emerged and sensitivity tests are therefore
important.
In complicated infection, chemotherapy is often unsatisfactory unless the underlying
abnormality is relieved. There is often a risk of causative sensitive organisms to be replaced
by resistant ones, making recurrent infection more difficult to manage.
‘Urethral Syndrome’ in Women (Abacterial Cystitis)
Nearly half the women who present with symptoms of UTIs (dysuria etc.) have sterile urine,
though the WBC content is sometimes raised.
© Dept of Clinical Microbiology 2003
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There are several causes. Some patients probably are in early stage of UTI or have
localised infections (any may respond to antibiotics). It is suggested that some may be
caused by micro-aerophilic or anaerobic vaginal organisms (Streptococcus, Lactobacilli or
Gardnerella), though this remains unclear. NB Similar symptoms may occur in several
other conditions, e.g. sexually transmitted urethritis, etc.
a)
Uncomplicated (primary) infection
Commoner in women. Accounts for perhaps 5% of consultations in general practice.
Very rarely causes renal damage, but is an important cause of ill health and
discomfort. Symptoms (dysuria, frequency, sometimes haematuria) are often acute.
Caused by single organisms (mixed growth suggests contamination: E. coli;
Proteus mirabilis (Staph. saphyrophyticus in younger women). Other infections are
rare, their presence suggests complicated infection.
In sexually active young women the causative organism is almost always E. coli (60%),
or Staph. saphrophyticus (30%), or Proteus mirabilis (10%). (Sexually activity may
however be irrelevant)
b)
Complicated (secondary) UTI
Often recurrent or chronic. Associated with underlying abnormality of urainry tract or
its nerve supply, e.g. prostatic obstruction, stone, congenital defect, vesico-ureteric
reflux (important especially in children), indwelling catheters, anything that prevents
complete bladder emptying.
Organisms
E. coli (about 40%), Proteus (various species), Pseudomonas, Klebsiella, other GNB,
Staph. albus, Staph. aureus, Strep. faecalis, Candida.
Incidence of symptomatic UTI
Infancy:
Young and Middle Aged:
Elderly
Male > Female (not known why)
Female >> Male (urethra shorter)
Male  (prostatism)
© Dept of Clinical Microbiology 2003
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Asymptomatic Bacteriuria (ASB or Covert Bacteriuria)
Bacteria 105 per ml. WBC usually <10 per mm3. Discovered on routine testing.
Approximate incidence in females:
Pre-school:
Middle-aged:
Over 60:
1%
5%
8%
Significance of ASB is often uncertain. In pregnancy, it should be detected in first trimester
by routine testing, and treated, otherwise, acute pyelonephritis may develop in later
pregnancy. ASS in males usually indicate underlying UT disease.
© Dept of Clinical Microbiology 2003
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Sequelae of Urinary Tract Infection
a)
b)
Renal Damage
Septicaemia
a)
Renal Damage
i)
ii)
iii)
Impairment of urine concentrating power
Necrotising papillitis
Chronic pyelonephritis
Progression of pyelonephritis is rare in absence of diabetes
Analgesic nephropathy or obstructive uropathy
Most important combination – VUR and UTI
New scars rarely develop after the age of four years
Progression to renal failure
i)
ii)
iii)
iv)
b)
Failure of kidney growth
Role of recurrent or persistent infection
Role of hypertension
Role of back pressure
Septicaemia
Neonates and prostatic obstruction
Groups where Urinary Tract Infection important:
Neonates:
Childhood:
Teenagers:
M>F
F>M
F>M
Pregnancy
Tumours, Calculi
Prostatic enlargement
Prolapse of uterus
Treatment
Septicaemia:
Non-septicaemia:
Parenteral
Non-parenteral
© Dept of Clinical Microbiology 2003
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