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.