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What is a urinary tract infection (UTI)?

A UTI is not just the presence of micro-organisms but also the inflammatory response to them, that can involve the upper or lower urinary tract.


What are the different types of UTI?

UTI's are classified based on whether they are complicated or uncomplicated depending on various factors.

UTI can either be:
- acute uncomplicated UTI
- acute uncomplicated pyelonephritis
- complicated UTI
- recurrent UTI

The difference between all of the above depends on the number (colony forming units) of bacteria per ml of urine on MSU urine culture.


What factors predispose to development of UTI?

These can be related to the host or the virulence factors of the infecting organism.

Host factors include:
- indwelling catheter
- breach of the bladder lining
- foreign body
- calculi
- diabetes
- urinary tract obstruction
- immunocompromise
- female pregnancy/ post menopausal


What microbe most commonly causes UTIs?

Most UTIs are caused by faecal derived bacteria, the commonest being gram negative bacilli such as E.coli E.coli causes 75-90% of uncomplicated UTI.
Other species include Klebsiella and Proteus.

E.coli possess an operon (FimH) coding for pili on the cell surface, which aids attachment to the urothelium. This helps them being washed out by urine flow and contributes to their ability to ascend to the upper urinary tract and cause infection there. The loss of this mechanical flushing effect in urinary tract obstruction results in urinary stasis and promotes bacterial growth.


Why are post menopausal women more likely to develop UTI?

Vaginal commensal bacteria are an important factor in preventing UTI. Specifically, Lactobacilli metabolise glycogen to lactic acid creating an inhospitable environment for uropathogens.

Atrophy of vaginal tissue following the menopause results in loss of lactobacilli. This is the rationale for use of topical oestrogens and live yoghurt to treat recurrent UTI.


Do patients with asymptomatic bacteriuria require treatment?

No. The majority of patients with indwelling catheters will develop bacteriuria. Although a foreign body is an important focus of infection, only patients who are symptomatic should be treated with antibiotics.


What is the difference between a complicated and an uncomplicated UTI?

An uncomplicated UTI is one occurring in a patient with a structurally and functionally normal urinary tract. A complicated UTI is one occuring in the presence of an underlying anatomical or functional abnormality. This distinction is important because it affects management.

Several factors can help distinguish complicated vs uncomplicated UTI, these include:
- male sex
- hospital acquired infection
- pregnancy
- indwelling catheter
- recent urinary tract intervention
- diabetes
- immunosuppression


UTIs can also be classified based on whether they affect the upper or lower tract. What symptoms can help distinguish between the two?

Lower urinary tract involvement tends to present with:
- frequency
- dysuria
- suprapubic pain
- haematuria

Upper tract involvement presents with:
- fever
- loin pain
- vomiting


What is the management of uncomplicated UTI in women?

UTI is much more common in women cf. men. Remember that uncomplicated UTI occurs in a normally functioning urinary system.

Diagnosis is made clinically and confirmed with urine dipstick. Nitrites and white cell dipstick result has a sensitivity of about 88%. MC&S is not routinely required for women with uncomplicated UTI. It should be undertaken however if there are risk factors for a complicated UTI, the woman has recurrent episodes, or has not responded to antibiotic treatment.

Treatment is usually with co-amoxiclav or trimethoprim.


What are the indications for further investigation in female UTI?

- development or signs of upper tract infection
- failure to respond to antibiotics
- recurrent infections
- factors suggestive of a complicated UTI
- pregnancy


What is sterile pyuria?

Occasionally, patients may present with symptoms of UTI but have no growth of organisms on microscopy and culture despite having persistent white cells on urinalysis.

This is called sterile pyruria. In the presence of persistent symptoms, non-visible haematuria, or sterile pyuria, the patient should be referred for a urology review to rule out an underlying malignancy or atypical infection such as TB.



= Acute renal infection
Occurs in small number of patients due to ascending infection from the lower urinary tract


Clinical features of pyelonephritis

Acute pain in one or both loins - radiates to iliac fossa or suprapubic region
Lumbar tenderness, guarding
Dysuria (due to cystitis in 30%)
Fever, rigors, vomiting and hypotension
Urinalysis - neutrophils, organisms, red blood cells and tubular epithelial cells

Hint: patients look unwell, shocked, with fever, leucocytosis and positive blood cultures


Complications of pyelonephritis

Caused by bacteriaemia
Renal or perinephric abscess (bulging, painful loin)
Papillary necrosis


Investigations in pyelonephritis

Urinalysis - bacteria, neutrophils
Renal tract USS/ CT - excludes perinephric collection and obstruction


Management of pyelonephritis

Adequate fluid intake
Antibiotics (first line co-amoxiclav and ciprofloxacin) given for 7-14 days
If severe, give initial i.v. therapy with a cephalosporin, fluoroquinolone or gentamicin