Urinary Tract Infections Flashcards
Introduction
The urogenital tract is a continuum - organisms can spread from one part to another
Upper part of the urethra is free of organisms
Urine in the bladder is regarded as being “sterile,” with occasional bacteria flushed out by micturition
Normal Flora
- outermost portion of urethra is colonised with bacteria commonly found on the skin
- Staphylococcus epidermidis
- Diphtheroids
- Lactobacilli
- Streptococci
- Occasionally intestinal bacteria
Urinary tract is usually invaded by microbes from the outside, via the urethra – ascending infection upwards
The presence of bacteria (bacteriuria) and inflammatory/ white blood cells (pyuria) indicate an infective process in the urinary tract
Majority of urinary infections =acute and short-lived, but contribute to a significant amount of morbidity
Severe infections result in the loss of renal function
Natural defenses of the Urinary Tract
Protective mucosal layer
Prostatic secretions
Low urine pH – acidic
High urea content
Mechanical flushing action and flow of urine
Vesico-ureteral valves that prevent reflux from the bladder
Peristalsis of the ureters
Ability to produce an inflammatory response (e.g. polymorphs/ neutrophils, - cytokines) and production of antibodies e.g. secretory IgA
Epidemiology
In neonates and very young children, UTI is more common in males/ boys & always needs further investigation – (structural abnormalities eg. posterior
urethral valves)
N.B. After infancy UTI =more common in females especially after puberty (related to sexual activity): Urethra= 20 cm in men whereas in women urethra =3-5 cm and is close to the rectovaginal orifices
Elderlies also more susceptible to UTI dt hormonal changes, prostate hypertrophy- males, urological procedures
Hospital acquired UTI: associated with presence indwelling urinary catheters, and surgery
1% catheterized patients will develop UTI within 3-4 days
Avoid/ Remove catheters as soon as possible to decrease risk
Predisposing Host Factors
Urinary tract obstruction and incomplete bladder emptying:
1.Pregnancy
Prostatic hypertrophy
Prolapsed uterus
Renal calculi ( P. mirabilis- struvite stones)
Tumours
Loss of neurological control of the bladder and
sphincters: paraplegics (neurogenic bladder), diabetes
mellitus (autonomic neuropathy), spina bifida,
multiple sclerosis
Anatomical abnormalities of the urinary tract e.g.
urethral strictures, post urethral valves
Vesico-ureteral reflux
Predisposing Environmental Factors
- Insturmentation/Urology surgical prrocedures
- Catheterisation/Indwelling Cathethers:
- Organisms are introduced directly into the bladder
- Facilitates bacterial access to the bladder via the lumen by tracking up between catheter and the urethral wall.
- Disrupts the normal bladder function and defence mechanisms - Sexual Intercourse:
- Facilitates movement of perineal organisms up the urethra, especially in females
- Short urethra close to anus and vagina
- Use of spermicides – reduces lactobacilli
Predisposing Virulence Factors
Adhesion, invasion, toxic products release , immune evasion/ suppression
- Pilli,fimbriae - allow organism to adhere to uro-epithelial cells.
- Afimbrial adhesins - allow adherence to uro-epithelial cells.
- Capsular acid polysaccharide (K) antigens – inhibits phagocytosis
- Haemolysins may act as membrane-damaging toxins.
- Proteus spp. produce urease - results in a high urinary pH.
Certain serotypes of E. coli (O25:H4), Klebsiella pneumoniae and Proteus spp. are common uropathogens
NB. More than 90% of uncomplicated UTI are caused by a single pathogen
Organisms associated with UTI’s
Bacteria:
- E. coli -most common cause infections of bladder (cystitis), and of kidney (pyelonephritis).
- K. pneumoniae
- Enterobacter species
- Proteus species
- Pseudomonas aeruginosa (catheters)
- Enterococcus species
- S. saprophyticus
- Corynebacterium urealyticum (D2)
Fungi:
- Candida albicans
- Trichosporon beigellii
Viruses:
-Adenovirus type II
Parasites:
-Schistosoma haematobium
Pathogenesis of UTI(1)
- Infections are commonly acquired via the retrograde, ascending route- entry through the urethra leading to bladder infection- cystitis
- Dissemination of infection from the bladder to the kidneys ( pyelonephritis)
- Dissemination from the kidneys into bloodstream => Septicemia = complication of UTI
Uropathogens e.g. E.coli commonly involved
- Haematogenous route of infection to kidneys - infection with other organisms originating from a distant source: e.g.
- Mycobacterium tuberculosis
- Salmonella typhi
- Staphylococcus aureus
- Candida spp.
Clinical Diagnosis of UTI’s
The diagnosis of UTI can be seperated into two components:
- Lower urinary tract infection (lower/uncomplicated UTI): Acute cystitis
- Upper urinary tract infection (upper /complicated UTI) -Acute pyelonephritis:
Clinical diagnosis
Lower urinary tract infection (lower/uncomplicated UTI): Acute cystitis
Rapid onset of dysuria: urgency, burning-BOM, frequency –FOM; and suprapubic pain
In the elderly and those with indwelling catheters, infection may be asymptomatic ( Asymptomatic bacteriuria)
Urethritis and vaginitis may cause similar symptoms.
Urine is turbid/cloudy due to neutrophils (pyuria) and bacteria (bacteriuria), may contain blood (haematuria)
Recurrent infections of the lower urinary tract occur due to:
- Persistent infection or relapse caused by the same organism
- Reinfection with a new organism
Clinical diagnosis
Upper urinary tract infection (upper/complicated UTI): Acute Pyelonephritis
Fever and flank pain
Often accompanied by lower tract symptoms at same time
Pyuria and bacteriuria present -laboratory
Organisms implicated are those that also cause lower tract infection
When Staphylococcus aureus is isolated, renal abscesses are often present and a remote/ endovascular source must be excluded.
Recurrent episodes of pyelonephritis result in loss of renal tissue/ scarring.
Laboratory Diagnosis:
Specimen Collection
- Aseptic technique: Collection of urine specimens:
- Collect urine specimen before starting antibiotic therapy
- Transport specimen to the laboratory without delay
- Urine is a good growth medium - delay between collection and culture will affect the results
- If delayed transportation: refrigerate specimen to avoid overgrowth of bacteria
- Aseptic technique: Collection of blood culture
- Collect blood culture before starting antibiotics if any signs of sepsis are present
Laboratory Diagnosis:
Collection of Mid-stream urine
Proper collection of the MSU specimen is very most important
All voided specimens will contain some bacteria.
Quantitative assay must be carried out.
Number bacteria colonies will be misleading unless contaminating bacteria are minimized
Patient must be informed how to wash genital area with soap (not an antiseptic) and water, and how to
collect specimen.
Urine to be collected in a sterile container after first 25 ml has been voided into the toilet and before the last amount voided in the toilet.
Laboratory Diagnosis:
Types of Urine Specimens
Catheter Specimens
Suprapubic Aspiration
Cystoscopy/Nephrostomy specimens
Catheter Specimens
Specimens with minimal contamination
Intermittent and long term
Danger of introducing organisms from the urethra into the bladder
Not performed routinely to obtain urine specimen
Specimen is collected from the catheter tubing - not the drainage bag
Suprapubic Aspiration
Using a needle and syringe - directly through abdominal wall
Only if cannot obtain a sterile specimen using other techniques
Cystoscopy/Nephrostomy Specimens
Specimens from the bladder or left and right ureter (ureteral specimen)
Laboratory diagnosis of UTI:
Specimen processing
- Macroscopic Examination:
- Clear, turbid, bloody - Microscopic Examination
- Uncentrifuged urine
- Wet preparation: Cell count: Neutrophils (pyuria), red blood cells (haematuria), epithelial cells, bacteria and yeast cells can be seen.
- Culture of Urine:
- Urine is cultured on different media for growth
- Semi-quantitative culture method used for colony counts, using calibrated loops
4. Biochemical Analysis for Identification of Bacteria: - Manual or automated tests
5. Antimicrobial Susceptibility Testing
Laboratory Diagnosis:
Colony counts
Diagnosis of an infection is based on the number of bacteria in the urine
1.More than 100 000 (10^5 CFU/ml
indicates infection =significant bacteriuria
- 1 000 (10^3) to 10 000 (10^4 bacteria per
ml in a symptomatic patient - probable infection - Less than 1 000 (10^3 ) bacteria per ml not
normally considered significant unless
symptomatic and one type grows
Single organism with inflammatory cells
Several types of bacteria and epithelial cells indicate
contamination.
NOTE:
- Guidelines and not absolute numbers.
- Criteria for significant bacteriuria only apply to midstream specimens
- Catheter, urethral and supra-pubic aspirate specimens use different criteria
- N.B. Specify specimen type on request form
-In these specimens any number of organisms may be significant
UTI Rapid diagnostic test
Urine dipstick- bedside test: Sensitivity low, but high specificity
Leukocyte esterase
Nitrites
Red blood cells
Protein
Sterile Pyuria:
Definition
Inflammatory white blood cells present in urine but no bacteria isolated from urine using routine culture methods
Sterile Pyuria:
Causes
1) Mycobacterium tuberculosis infections
2) Chlamydia and Mycoplasma infections
3) Prior antibiotic therapy
4) Neoplasms
5) Kidney stones
6) Fastidious organisms, not detected with standard routine culture methods
Host Factors to consider for UTI treatment
Age
First episode/ recurrent infection
Uncomplicated/ complicated UTI
Asymptomatic bacteriuria
Indwelling catheter present/absent
Symptomatic treatment vs curative
No treatment at all / bladder wash out
Pregnancy
Prophylaxis vs abortive treatment
General Factors to consider for UTI treatment
Majority of Gram-negative bacilli causing UTI produce betalactamase enzymes- resistant to ampicillin and amoxicillin
Urinary antiseptics only for uncomplicated UTI
Asymptomatic bacteriuria should be treated in the following patients: pregnant, renal transplant, invasive procedures
Follow-up cultures should be done after treatment (2 weeks later) to confirm eradication of the organism.
Removal of catheter important esp candiduria
