Urinary Tract Infections (UTI)

Definition

• UTI is defined as the presence of micro-organisms in the urinary tract.

• Most patients with UTI have significant bacteriuria, i.e. more than 105 CFU/ml, in a suitably collected mid-stream urine.

Types of UTI

• Urethritis

• Cystitis

• Acute bacterial pyelonephritis

Pyelonephritis

• An infection of the upper urinary tract (kidney).

• Common clinical symptoms include: fever, and flank pain accompanied with bacteriuria and pyuria.

Cystitis

• An infection of the lower urinary tract (bladder).

• Common clinical symptoms include; urgency, frequency, and pain on urination,, and occasionally fever.

Pathogenesis and route of transmission

Organisms from the faecal flora usually enter the urinary tract by;

1. Direct or ascending route; via the urethra to the urinary bladder and the kidney where they multiply and produce toxins, the female are more prone to infection because of short urethra.

2. Blood; from septic focus causing bacteremia and UTI.

Predisposing factors

• Age; Incidence increase gradually with age.

• Sex; The short female urethra greatly predisposes to infection of UT by ascending route.

• Instrumentation and surgery. • Other host factors as; D.M and

immunosuppresion by steroids or cytotoxic drugs.

Commensals

• Urinary tract is normally sterile, except of urethra which may contain a few commensals such as acinetobacter species, and diptheriods. Yeast may also be found in the female urethra.

• Contamination of the urine with skin commensals including staphylococci, dipththeroids, and mycobacterium smegmatis may occur as a specimen is being collected.

• In female patients, the urinary may become contaminated with organisms from the vagina (epithelial cells)

Causative organisms

• Gram +ve: Enterococci, Staphylococcus saprophyticus.

• Gram –ve: Escherichia coli, Proteus species, Pseudomonas aeruginosa, Klebsiella strains.

• Also: Mycobacterium tuberculosis

Escherichia coli

• E. coli (serotypes: 02, O4, O6) which are fimbrinated strains adhering to uro-epithelial cells, leading to colonization and infection is the commonest cause of urinary tract infections.

Gram negative bacilli

• Pseudomonas, Proteus, and Klebsiella infections often follow catheterization and gynecological surgery (nosocomial pathogen).

• Infection with proteus may be complicated by phosphate stone formation as it is urea leads to alkaline pH.

S. saprophyticus

• Infection more common in young women.

Specimen collection

• Samples should be collected before the start of antibiotics.

• Transport within 2 h. if delay is suspected then refrigeration at 4C or boric acid.

• Mid stream urine.

• Adhesive bags; in infants.

Macroscopic examination

• Pus, blood and turbidity.

• Strip: nitrite for infection/ leukocyte esterase for pyuria/ pH for proeus.

• Microscopic examination;

1. Epithelial cells.

2. Leuckocyte.