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Urinary Tract Infections Reading: pg. 241 – 248

Introduction
Acquisition and etiology (fig. 20.1, pg. 241)
- Escherichia coli
- Viral
- Parasitic
Pathogenesis (fig. 20.2, pg. 242)
- Mechanical factors
  - Obstructions
  - Catheters (fig. 20.3, pg. 243)
- Virulence factors
- Resistance to bacterial colonization
Clinical features and complications
- Acute lower UTIs
  - Pyuria
  - Bacteriuria
  - hematuria
- Recurrent infections
- Upper UTIs
  - pyelonephritis
Laboratory diagnosis
- Collection
- Special collection
Treatment (fig. 20.8, pg. 247)

Urinary tract infections

Introduction

n Urinary tract infections common in women, not as common in men.

n Most UTIs are acute and short-lived.

Female urinary organs

Acquisition and etiology

n    Bacteria enter urinary system through urethra (Ascending route from urethra to bladder)

n    Infection may proceed to the kidneys

n    Invasion of bloodstream result in septicemia à spread to kidneys.

n    fig. 20.1 Common causes of urinary tract infections in two settings, community-acquired and hospital-acquired (nosocomial)

n    Nosocomial-acquired UTIs - associated with use of catherers

–     Escherichia coli – most common cause of ascending UTI

n     80% of community acquired UTI, 40% in hospital

n     Other gram negative rods – also cause UTIs in hospital setting (due to their resistance to antibiotics)

Acquisition and etiology

– Viral

– Viral causes of UTI is rare

– Some associations with:

§ hemorrhagic cystitis (human polyomaviruses, adenovirus)

§ other renal diseases (hantavirus, mumps, HIV)

– Parasitic

–    Very few cause UTIs

–    Fungi – Candida spp., Histoplasma capsulatum

–    Protozoan – Trichomonas vaginalis

–   causes urethritis in males and females, vaginitis in females

–    Worms – Schistosoma haematobium

§    eggs penetrate bladder wall and may become calcified

§    Chronic infections à bladder cancer

§    Inflammatory response can lead to obstruction of ureter à hydronephrosis

Pathogenesis

n    Mechanical factors that predisposes an individual to UTIs

n    fig. 20.2 Host factors

n   Obstructions: Anything that disrupts urine flow or complete emptying of bladder

n   Shorter female urethra – more susceptible to UTI

n   Sexual intercourse moves microbes up urethra

n   Male infants – UTI more common in uncircumcised males

n    Bacterial attributes

n   Capsules

n   Enzymes – hemolysins, urease

n   Fimbriae

Pathogenesis

Main causes of obstruction to complete bladder emptying

• Loss of neurologic control of bladder and sphincters (spina bifida, paraplegia, MS)

• Large residual urine in bladder - obstruction to urine flow

• Vesicoureteral reflux (reflux of urine from bladder up ureters)

• common in children with anatomic abnormalities of urinary tract

• Predisposed to ascending infection and kidney damage

• People with diabetes mellitus

• UTIs more severe, more persistent

Mechanical factors

n Catheters: major predisposing factor for UTI

n During insertion – carries bacteria into bladder

n While in situ

n fig. 20.3

Virulence factors

n   Most urinary tract pathogens are fecal flora

n   Only aerobic and facultative species

n   Must have virulence factors required to colonize and infect urinary tract

n   E. coli serotypes capable of causing UTIs = UPEC (uropathogenic E. coli)

n   Possess genes not found in fecal E. coli

§   Fimbriae – allow adherence

§   Capsular acid polysaccharide (K) antigens – inhibits phagocytosis

§   Hemolysins – acting as membrane-damaging toxins

n   Proteus – produce urease

§   Causes pyelonephritis and stones

Resistance to bacterial colonization

n   A healthy urinary tract is resistant to bacterial colonization

n   pH

n   Chemical content

n   Flushing action of urine

n   All prevent colonization and multiplication of bacteria

Clinical features and complications

n   Lower urinary tract infections – limited to bladder

n   Acute lower UTIs characterized by:

n   Dysuria

n   Urgency

n   Frequency of micturition

n   Urine is cloudy due to:

n   Pyuria

n   Bacteriuria

n   Hematuria

n   Diagnosis confirmed by:

n   Examination and culture of urine specimen

Clinical features and complications

n   Recurrent infections due to:

n   Same strain of organism

n   Infection by different organism

Clinical features and complications

n    Upper UTIs

n   Pyelonephritis (infection of the kidney)

n    Symptoms: lower urinary tract symptoms and fever

n    Cause - Staphylococci

n    Renal abscess present

n    Recurrent infection à loss of renal function à hypertension à renal damage

n    Stone formation à obstruction of renal tract

n    Hematuria – feature of endocarditis, immune complex disease and infection of kidneys

n    Pyuria – kidney infection by M. tuberculosis

n    Asymptomatic infection (bacteria in urine) – important in:

n    Pregnant women and young children

n    People undergoing instrumentation in urinary tract à may proceed to bacteremia

n    Elderly and diabetics – both risk factors for asymptomatic bacteriuria

Laboratory diagnosis

n   Urine in bladder is normally sterile

n   Collection

n   Usual method of collection

n   Midstream urine (MSU) collected into sterile container

§   Bacteriuria is “significant” if MSU contains >10^5 organisms/ml, usually only a single species

§   Contamination: <10^4 organisms/ml and contain more than one species

§   numbers do not pertain to samples obtained by catheters or aspirated directly from bladder

Laboratory diagnosis

n   Special collection

n   Babies and children

n   Urine bags – usually heavily contaminated

n   Suprapubic aspiration of urine directly from bladder

n    Catheters – collected from catheter tube using needle and syringe, not from bag

n    Collection for detection of M. tuberculosis

n   early morning samples taken on 3 consecutive days

n Examination of urine sample:

n    Done promptly to avoid multiplication of bacteria

n    Microscopic:

n   number of bacteria à infection or contamination

n   Presence of blood à >10 WBC/ml is abnormal

n   Pyuria à may indicate infection even if sample is sterile

n    Culture methods

Treatment

§ Uncomplicated UTI (cystitis)

§ Antibiotic given as single dose or for 3 days

§ Choice of agent depends on susceptibility tests

§ Fig. 20.8 common oral antibiotics for urinary tract infections

§ Large volume of fluid to flush bladder

§ Recheck for eradication of infection

Treatment

§ fig. 20.8

Treatment

n Complicated UTI (pyelonephritis):

n   Systemic treatment with antibiotic based on susceptibility tests

n   Treatment continued until signs and symptoms subside

n   Replace with oral therapy

Prevention

n Healthy women:

n Empty bladder regularly – washes bacteria out especially following intercourse

Urinary tract infections

Introduction

n Urinary tract infections common in women, not as common in men.

n Most UTIs are acute and short-lived.

Female urinary organs

Acquisition and etiology

n Bacteria enter urinary system through urethra (Ascending route from urethra to bladder)

n Infection may proceed to the kidneys

n Invasion of bloodstream result in septicemia à spread to kidneys.

n fig. 20.1 Common causes of urinary tract infections in two settings, community-acquired and hospital-acquired (nosocomial)

n Nosocomial-acquired UTIs - associated with use of catherers

– Escherichia coli – most common cause of ascending UTI

n 80% of community acquired UTI, 40% in hospital

n Other gram negative rods – also cause UTIs in hospital setting (due to their resistance to antibiotics)

Acquisition and etiology

– Viral

– Viral causes of UTI is rare

– Some associations with:

§ hemorrhagic cystitis (human polyomaviruses, adenovirus)

§ other renal diseases (hantavirus, mumps, HIV)

– Parasitic

– Very few cause UTIs

– Fungi – Candida spp., Histoplasma capsulatum

– Protozoan – Trichomonas vaginalis

– causes urethritis in males and females, vaginitis in females

– Worms – Schistosoma haematobium

§ eggs penetrate bladder wall and may become calcified

§ Chronic infections à bladder cancer

§ Inflammatory response can lead to obstruction of ureter à hydronephrosis

Pathogenesis

n Mechanical factors that predisposes an individual to UTIs

n fig. 20.2 Host factors

n Obstructions: Anything that disrupts urine flow or complete emptying of bladder

n Shorter female urethra – more susceptible to UTI

n Sexual intercourse moves microbes up urethra

n Male infants – UTI more common in uncircumcised males

n Bacterial attributes

n Capsules

n Enzymes – hemolysins, urease

n Fimbriae

Pathogenesis

Main causes of obstruction to complete bladder emptying

• Loss of neurologic control of bladder and sphincters (spina bifida, paraplegia, MS)

• Large residual urine in bladder - obstruction to urine flow

• Vesicoureteral reflux (reflux of urine from bladder up ureters)

• common in children with anatomic abnormalities of urinary tract

• Predisposed to ascending infection and kidney damage

• People with diabetes mellitus

• UTIs more severe, more persistent

Mechanical factors

n Catheters: major predisposing factor for UTI

n During insertion – carries bacteria into bladder

n While in situ

n fig. 20.3

Virulence factors

n Most urinary tract pathogens are fecal flora

n Only aerobic and facultative species

n Must have virulence factors required to colonize and infect urinary tract

n E. coli serotypes capable of causing UTIs = UPEC (uropathogenic E. coli)

n Possess genes not found in fecal E. coli

§ Fimbriae – allow adherence

§ Capsular acid polysaccharide (K) antigens – inhibits phagocytosis

§ Hemolysins – acting as membrane-damaging toxins

n Proteus – produce urease

§ Causes pyelonephritis and stones

Resistance to bacterial colonization

n A healthy urinary tract is resistant to bacterial colonization

n pH

n Chemical content

n Flushing action of urine

n All prevent colonization and multiplication of bacteria

Clinical features and complications

n Lower urinary tract infections – limited to bladder

n Acute lower UTIs characterized by:

n Dysuria

n Urgency

n Frequency of micturition

n Urine is cloudy due to:

n Pyuria

n Bacteriuria