Urinary Tract Infection - UTI

Original article by Tom Leach | Last updated on 7/6/2014
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Introduction

These are very common in women, but far less common in men and children.
Recurrent infection can lead to considerable morbidity and may even lead to renal disease, and possibly end stage renal failure.
It is also a source of life-threatening Gram-negative septicaemia.
 

Epidemiology

  • Urinary tract infections are much more common in women. 50% of women will suffer from a UTI in their lifetime.
  • About 3% of 20 year old women have a UTI at any one time. This increase by 1% with each decade of life.
  • UTI’s are pretty uncommon in men, except during the first year of life, and over the age of 60.
  • UTI’s account for 1-2% of all patients in primary care.
  • About 30% of catheterized patients have a UTI.
 

Aetiology

  • In women, often the urinary tract is anatomically normal.
  • In contrast, in men and children where UTI’s are much less common, then there often is an anatomical abnormality.
  • Infection is most commonly due to the bacteria in the patient’s own bowel – and the most common route of transmission is up the urethra, although it can get there through blood, lymphatics or a fistula.
  • A UTI infection can affect any part of the urinary tract. The most common place is in the bladder. Site of infection are classified as follows:
    • Bladder – cystitis
    • Prostate – prostatitis – this is the most common site of presentation in the male.
    • Renal pelvis - Pyelonephritis
  • UTI’s are more common in sufferers of diabetes.
  • E. coli is the major cause of UTI’s – it is responsible for >70% of cases in the community, and >41% of cases in hospital.
 

Pathology

Symptom severity is determined by the type of bacterial infection, however, tissue damage is due to the level of inflammation and injury caused by the hosts own immune system.
Virulence –this is dependent upon certain characteristics of the infecting organism.to be successful in causing an infection, bacteria should have:

  • Flagellae – for motility
  • Aerobactin – for acquiring iron in an iron poor environment
  • Adhesions – these are the most important as they enable the bacteria to adhere to the epithelial cells of the urinary tract. There are two main types of E. Coli, one with adhesion molecules better suited to the bladder, and the other with adhesion molecules more suited to the renal pelvis.

Other implicated factors

  • Urine pH and osmolality – the greater the osmolality, the less likely the bacteria are to survive. If the pH is particularly high or particularly low then this is also likely to reduce bacterial survival.
  • Commensal organisms – other bacteria are actually involved in normal host defence – they prevent E. Coli from overgrowing. these other bacteria can be killed by spermicidal gel or disruption by antibiotics, and as such, these agents are often advised against.
  • Urine flow / micturition – these wash out bacteria, and thus urine stasis promotes UT infection.
 

Natural history

  • 90% of UTI’s are isolated events, only 10% are part of a patients recurring infection pathology. Of those with recurring infection, 20% will relapse (this is where the same infection occurs within less than 7 days after treatment), whilst 80% will become re-infected (this is where there is a period of 14 days or more without infection, and then the patient may be infected again, with the same or a different organism – re-infection involves a separate infection, relapse is the same infection that just hasn’t cleared up.)
  • Uncomplicated UTI – this is a UTI where the anatomy of the urinary tract is normal, and renal imaging will be normal. There will be no underlying condition contributing to infection. This is unlikely to result in serious kidney damage.
  • Complicated UTI -  this will occur in urinary tracts with stones, and also in diabetes (as a result of the kidney damage caused by diabetes). The recurrent infections can themselves contribute to stone formation. The combination of recurrent infection and urinary tract obstruction can result in sever and rapid kidney damage. In these conditions there is a risk of Gram-negative septicaemia.
  • You should always assume in MEN that a UTI is complicated until proven otherwise.
 

Acute Pyelonephritis

This is acute kidney infection.
This will often present with fever, loin pain, tenderness and significant bacteriuria.
There may be small renal abscesses and streaks of pus in the renal medulla.
Histologically you can see infiltration with leucocytes.
CT scans will often show ‘wedge-shaped’ areas of inflammation, although if treated with antibiotics it will rarely cause permanent kidney damage.
 

Reflux Nephropathy

This was in the past called chronic pyelonephritis.
It results from a combination of
  • A compromised vesicoureteric valve (the valve that separates the ureters from the bladder)
  • Infection in infancy or early childhood.
Normally, the vesicoureteric junction acts as a one-way valve, allowing urine to enter from above, but not leave the bladder via this route when the bladder contracts.
In some infants and children, this valve is compromised. This results in a jet of urine shooting up the ureter upon emptying the bladder. This is also associated with incomplete bladder emptying, and incomplete bladder emptying predisposes infection. The reflux of urine also leads to kidney damage.
 
Diagnosis –on CT scan the kidneys will appear irregular, and may be reduced in size. The condition can be unilateral or bilateral, and may affect all or only part of the kidney.
Reflux often subsides around the age of puberty, when the base of the bladder grows, however by this time, the damage may have already been done. Renal function can decline, even if there is no further infection, due to fibrosis of the renal tissue.
 
If the condition is chronic and does not resolve with age after being acquired in infancy, then it is likely to cause end-stage renal failure in childhood or adult life.
Having this condition in child-hood also predisposes to hypertension in later life.
 
Reflux nephropathy cannot occur in the absence of reflux, and it does not begin in adult life. So, adult females with bacteriuria and a normal urogram* can be reassured that kidney damage will not develop.
* An X-ray of the urinary tract
 

Aet​iology

  • Being female
  • Sexual intercourse
  • Exposure to spermicide in females
  • Pregnancy
  • Menopause
  • Immunosuppression
  • UT obstruction
  • Catheterization – in catheterisation the urine is almost always infected, so it is pointless sending samples for testing, or treating unless the patient is ill.
  • Constipation can impair bladder emptying. 
 

Clinical presentation of UTI

  • Frequency of micturation (both day and night)
  • Pain on voiding (dysuria)
  • Suprapubic pain and tenderness
  • Haematuria
  • Smelly urine
  • Pyuria (pus in the urine)
These symptoms are related to bladder and urethral inflammation, and they are the lower urinary tract symptoms (LUTS)
  • Loin pain, fever, oliguria (extremely low urine output) and systemic symptoms suggest involvement of the pelvis of the kidney – pyelonephritis / pyelitis.
  • HOWEVER, be wary, as localisation of the infection by symptoms alone is unreliable.
  • UTI’s may also present with no symptoms, or atypical symptoms, such as abdominal pain, fever and nocturia.
  • Children may also present in unusual ways, and UTI should always be considered in children who ‘fail to thrive’.
 
You need to excrete a minimum of 500ml urine a day to be able to remove all the toxins from your blood – if you are excreting less than this, then you aren’t removing enough to remove your toxins – as a result, blood urea levels will be raised.
 

Investigations

MSU – dipstick – these tests can be unreliable, so don’t take them as gospel.

  • Most Gram-negative bacteria will reduce nitrates to nitrites and thus the dipstick test for nitrites can be an indicator of infection. There are many false positives for this test.
  • Leukocytes esterase may also be present in the sample – and this shows the presence of pyuria. Thus a dipstick test that shows both esterase and nitrites will be highly suggestive of bacterial infection (sensitivity of 75%, specificity of 82%).

MSU – analysis – you can also send the sample off to the lab for more accurate analysis:

  • Bacteria of greater than 105 in the urine allows for diagnosis
  • Bacteria of greater than 102 in the presence of pyuria allows for diagnosis.
 

Presentations without signs of infection

These can include:
  • Postcoital bladder trauma
  • Vaginitis
  • Urethritis (in the elderly)
  • Interstitial cystitis (Hunner’s Ulcer) – this is rare and usually affects women over 40. There4 are inflammatory changes of the UT, including often ulceration of the base of the bladder. Many people believe this to be an autoimmune disorder. There are various treatment options, with varying degrees of success. These can include oral prednisolone or blader instillation of sodium cromoglicate.
  • In sterile young women with pyuria, then Chlamydia and tuberculosis are possible.
 

Management

In primary care, a dipstick test positive for nitrites and leukocytes is enough to make a positive diagnosis.
Generally ciprofloxacin and co-amoxiclav are used against resistant organisms.
In patients who present for the first time with loin pain, fever and tenderness, then URGENT ULTRASOUND should be requested to exclude the possibility of obstructed pyonephrosis. If this is present, then it can be drained by percutaneous nephrostomy.
 

One-off presentation

Drink lots!(>2L / day) – encouraging the patient to drink a lot of fluids will ensure they urinate often. The patient should also be encouraged to drink lots for a couple of weeks after the infection appears to have passed.
Before you have identified the organism; treat as follows:

  • Cystitis – Trimethoprim – 200mg/12 hours – 3 days course in women, 7 days course in men. Given orally. Alternatives include ciprofloxacin and co-amoxiclav.
  • Pyelonephritis – Cefuroxime / Ciprofloxacin. Usually given intravenously initially until symptoms begin to improve (~8 hours), then orally for 7 days.
  • Prostatitis - Ciprofloxacin
 

Recurrent presentation

  • You should take urine cultures to establish if it is relapse or reinfection.
  • Relapse – you should try to identify a cause for the relapse – such as stones or scarred kidneys if anything is found, then this should be treated. If nothing is found, try IV antibiotics for 7 days, then oral antibiotics for 4-6 weeks. If still relapses occur, then you should consider long term antibiotics.
  • Re-infection – this implies poor bladder defence mechanisms. Contraceptive practice should be reviewed (use of diaphragm and spermicidal gel should be discouraged). Patients should take preventative measures (basically the opposite of the aetiological factors, and drink lots!)