Pathophysiology of the Disease
Urine is an ideal medium for bacterial growth. Factors that make it less favorable for
bacterial growth include: a pH less than 5, the presence of organic acids and high
levels of urea. Frequent urination and high urinary volumes are also known to
decrease the risk of UTI.
Uncomplicated UTI is usually considered to be cystitis or pyelonephritis that occurs
in premenopausal adult women with no structural or functional abnormality of the
urinary tract and who are not pregnant and have no significant comorbidity that
could lead to more serious outcomes. Also, some experts consider UTIs to be
uncomplicated even if they affect postmenopausal women or patients with wellcontrolled diabetes. In men, most UTIs occur in children or older patients, are due to
anatomic abnormalities or instrumentation, and are considered complicated. Sexual
intercourse is a common cause of a UTI as it promotes the migration of bacteria into
the bladder. People who frequently void and empty the bladder tend to have a lower
risk of a UTI.
Complicated UTI can involve either sex at any age. It is usually considered to be
pyelonephritis or cystitis that does not fulfill criteria to be considered uncomplicated.
A UTI is considered complicated if the patient is a child, is pregnant, or has any of the
following:
 A structural or functional urinary tract abnormality and obstruction of urine
flow
 A comorbidity that increases risk of acquiring infection or resistance to
treatment, such as poorly controlled diabetes, chronic kidney disease, or
immunocompromise
 Recent instrumentation or surgery of the urinary tract
Bacteria that cause UTIs tend to have adhesins on their surface which allow the
organism to attach to the urothelial mucosal surface. In addition, a short urethra also
makes it easier for the uropathogen to invade the urinary tract. Premenopausal
women have large concentrations of lactobacilli in the vagina and an acidic pH which
prevents colonization with uropathogens. However, the use of antibiotics can erase
this protective effect.
TREATMENT GUIDELINES
The treatment has varied historically from 3 days to 6 weeks. There are excellent cure
rates with “mini-dose therapy” which involves three days of treatment. E.
coli resistance to common antimicrobials varies in different areas of the country, and
if the resistance rate is greater than 50% choose another drug.
Trimethoprim/Sulfamethoxazole for 3 days is good mini-dose therapy, but resistance
rates are high in many areas. It should not be used if local resistance is >20%. Firstgeneration cephalosporins are good choices for mini-dose therapy. Nitrofurantoin is
a good choice for uncomplicated UTI, but it is bacteriostatic, not bactericidal, and
must be used for 5 to 7 days. Fluoroquinolones have high resistance but are a favorite
of urologists because of high tissue penetration levels, especially in the prostate. For
this reason, fluoroquinolones are not preferred except for complicated infections and
those involving the prostate. Recent precautions from the FDA about fluoroquinolone
side effects should be heeded.
Recently, the FDA approved Fosfomycin as a single-dose therapy for uncomplicated
UTIs caused by E coli. Adjunctive therapy with phenazopyridine for several days may
help provide additional symptom relief.
Even without treatment, most UTIs will spontaneously resolve in about 20% of
women; especially if increased hydration is used. The likelihood that a healthy female
will develop acute pyelonephritis is very small.
Asymptomatic bacteriuria is quite common and requires no treatment, except in
pregnant women, those who are immunosuppressed, have had a transplant or
recently underwent a urological, surgical procedure.
REFERENCE: Michael J. Bono; Wanda C. Reygaert. Urinary Tract Infection.
[Update: June 23, 202] In: StatPearls [Internet]. Treasure Island (FL): StatPearls
Publishing;
2022
Jan-.
Available
from:
https://www.ncbi.nlm.nih.gov/books/NBK470195/
https://www.msdmanuals.com/professional/genitourinary-disorders/urinarytract-infections-utis/bacterial-urinary-tract-infections