URINARY TRACT INFECTIONS (UTI)
Contents:
1) Introduction
2) Etiology and acquisition
3)Pathogenesis (bacterial virulence factors, host defence mechanisms, factors
predisposing to infections)
4) Clinical categories ( lower and upper urinary tract infections)
5) Examination of the patient with UTI (physical, laboratory, microbiological, using
imaging techniques)
6) Treatment and prevention
Ad 1) Introductions
- UTI = one of the most common infections, usually bacterial, often nosocomial
- frequent in women (20-30% of them have a UTI at some time in their life,
sometimes reccurently)- anatomical disposition, pregnancy, hormonal changes and
vagina pH, in men up to 2 years of age and more than 55 years of age,
- clinical features are various and have different course (from asymptomatic
bacteriuria to sepsis),
- infected urine is cloudy ( due to presence of pus cells and bacterias and red blood
cells = pyurie, bacteriuria, haematuria) and smelling,
- normal urine is sterile, has pH 4,5-8, without protein, glucosa, bilirubin,
urobilinogen, blood.
Ad 2) Etiology and acquisition
Etiology:
a) bacterial: the most frequent
- Gram-negative strains (E.coli, Klebsiella, Proteus, Pseudomonas, Enterobacter,
Providentia, Serratia)+ Chlamydia spp., Ureaplasma spp.
- Gram-positive strains (Enterococcus, Staphylococcus) : more often in hospitalized
patients
b) viral (adenovirus, CMV, HSV, VZV)
c) fungal ( Candida, Histoplasma)
d) protozoal (Trichomonas)
e) parasitic (Schistosoma)
Acqusition:
a) by ascending route: bacterial infection is usually acquired by the ascending route
from the urethra to the bladder and may proceed to kidney, ocasionally bacteria
infecting the urinary tract invade the bloodstream to cause septicaemia.
b) by hematogenous spread: less commonly infection may result from hematogenous
spread of an organism to kidney, with the renal tissue being the first part of the tract
to be infected.
c) by lymphogenous route or per continuitatem: rarely (from cervix or
rectosigmoideal area or due to perineal absces)
Ad 3) Pathogenesis
Normaly the balance exists between the host defence mechanisms and the bacterial
virulence factors.
a) Host defence mechanisms:
With the exception of the uretral mucosa, the normal urinary tract is resistant to
bacterial colonisation and usually eliminates microorganisms rapidly and efficiently
thanks to:
the washing-out mechanism of the urine,
the pH of the urine and vagina,
the chemical content of the urine,
the presence of secretoric IgA antibodies in the mucosa.
b) Bacterial virulence factors:
The ability of some serogroups of E.coli to adhere to urethral and bladder epithelium
is based on presence of fimbriae (pili).
Some uropathogens, i.e.Proteus spp., have special enzymes (urease or haemolysins)
ensuring some substances necessary for bacterial metabolism (iron...).
The presence of the capsular antigen protects Enterobacteriacae from the phagocytosis
and the bactericidal effect of the blood serum.
c) Factors predisposing to infection:
Mechanical factors are important. Anything that disrupts normal urine flow or
complete emptying of the bladder, or facilitates access of organisms to the bladder,
will predispose an individual to infection.
(Obstruction due to lithiasis, tumours, prostatic hypertrophy, pregnancy, strictures of
any sorts including congenital malformations ,
functional neuromuscular disorders e.g. spina bifida, paraplegia or multiple sclerosis,
and also iatrogenic reasons -catheterization).
Presence of some metabolic or immunologic disorder can also predispose infection
( i.e. diabetes mellitus decompensation).
From this point of view we can clinically distinguish complicated and uncomplicated
UTIs.
Ad 4) Clinical categories of UTI
a)
-
Upper urinary tract infections:
acute and chronic pyelonephritis
interstitial nephritis
renal abscess, perinefritic abscess
b)
-
Lower urinary tract infections:
cystitis
uretritis
prostatitis
Ad 5) Examination of the patient with UTI
a) Clinical examination:
- Anamnesis:
Acute infections of the lower urinary tract are characterized by rapid onset of
dysuria (= burning pain on passing urine), urgency (= the urgent need to pass urine)
and frequency of micturition. The body temperature is usually normal or subfebrile.
Acute infections of the upper urinary tract are characterized by lumbalgias (=
unilateral or bilateral pain in the lumbar area), high body temperature, meteorism,
sometimes nausea and vomiting.
- Physical examination:
Inspection of the external part of uretra and genitalia, abdominal palpation,
tapottement, Israeli point
In infants symptoms are often unspecific: subfebrile body temperature, gastrointestinal
complaints, loss of apetite, non-prosperity, in children sometimes enuresis.
b) Laboratory testing:
Blood:
Inflammatory signs - erythrocyte sedimentation rate (ESR), blood count, differential
count, CRP, blood culture
Biochemistry of the serum - urea, creatinin, natrium, potassium, chlorine ionts
Urine:
Biochemistry - pH, presence of protein, glucose, blood, bilirubuin, urobilinogen
Microscopy of urine sediment - presence of leucocytes, erythrocytes, cylindres,
epitelia, bacterias, mucus, crystals
Microbiological investigation
Microbiological investigation (urine cultivation):
In health the urinary tract is sterile, although the distal region of the urethra is
colonized with commensal organisms which may include periurethral and faecal
organisms.
Bacteriuria is defined as significant, when a properly collected midstream urine
specimen is shown to contain more than 105 organisms per ml. Infected urine usually
contains only a single bacterial species. Contaminated urine usually has less than 10 4
organisms per ml and often contains more than one bacterial species. Distinguishing
infection from contamination when counts are between 104 and 105 organisms per ml
can be difficult.
The most often urine specimen for microbiological examination is a midstream urine
sample (MSU), i.e. the urine obtaining after micturiting the first part of urine stream,
which helps to wash out contaminants in the lower urethra.
This should be collected into a sterile, wide-moithed container after careful cleansing
of the labia or glans with soap (not antiseptic) and water.
Collection of MSU samples from babies and young children is difficult and can be
realized with a help of bag urine. This is plastic bag sticked to the perineum in girls or
to the penis in boys.
Next possibility how to obtain urinary sample is suprapubic aspiration of urine by a
sterile needle directly from the bladder, or by cathetrisation of the urethra.
c) Imaging techniques:
Ultrasonography
Radiography - native scan
I.v. urography
Radionuclear nephrography
Computerized tomography
Ad 6) Treatment
a) High fluid intake oral or parenteral, complete bladder emptying (a postvoiding
urine volume of more than 100 ml is associated with UTI).
b) Symptomatic therapy (spasmoanalgetics), if necessary.
c) Causative therapy (antibiotics oraly or parenteraly, if possible according to
susceptibility of the etiologic agent).