Micro Chapter 63: Urinary Tract Infections
UTIs are the most common bacterial infection in humans
Can happen in both men and women
1/5 girls will have a UTI by age 30, and over half will have a UTI in their life
UTIs can happen at any part of the urinary tract – including the bladder, kidneys, and prostate in men
Urethritis – infection of the urethra, and is characteristic fo some STDs, like gonorrhea and chlamydia
Acute uncomplicated UTI – a UTI that presents as acute cystitis (bladder or lower-tract infection) in
otherwise healthy women
Acute nonobstructive pyelonephritis (aka acute uncomplicated pyelonephritis) – kidney infection or
upper tract infection in otherwise healthy women
Complicated UTI – UTI in people with underlying structural or functional abnormalities of the GU
Asymptomatic bacteriuria – bacteria in the urine, but no signs or symptoms of UTI
Bacterial prostatis – bacterial infection of the prostate
Chronic bacterial prostatis – chronic bacteria in the prostate causing recurrent or persistent pelvic or
urinary symptoms in men
A person who’s had a UTI is at risk for a future one
Reinfection – if a new organism is isolated, or a previously isolated organism is reintroduced
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Reinfection in UTIs happens when a previously isolated organism is reintroduced into the
urinary tract from the colonizing gut or genital flora
Relapse – UTI that resists drugs and stays in the GU tract
UTI usually happens when colonizing flora from the periurethral area, or vagina in women, ascend up
the urethra into the bladder
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Bacteria causing UTI usually originate from the normal gut flora
UTI happens more often in women, because of the shorter female urethra, allowing easier
access of bacteria to the bladder
Most bacteria that ascend to the bladder, will be removed with the next normal urination
For infection ot happen, bacteria must be able to persist and reproduce int eh bladder
Pyelonephritis happens when organisms go further up to the kidneys
o Can happen when the bacteria have adhesins, or from reflux up the ureter in people
with incompetent ureteral sphincters
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Bacterial infection of the prostate gland also happens mainly through ascension of organisms
form the urethra into the prostate ducts
o This is facilitated by turbulent urine flow, which is common in men with prostate
hypertrophy
Occasionally, UTI can happen from spread of organism through the blood from somewhere else
o The characteristic feature of hematogenous dissemination (spread through blood) is
renal abscesses in the renal cortex
o UTIs from blood are usually S. aurea or candida
The most important pathogen in UTI is E. coli, but other bacteria can cause UTI
Uncomplicated UTI:
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Uncomplicated UTI will be E. coli 80-85% of the time
o An essential E. coli virulence characteristic for acute cystitis is expression of mannosesensitive fimbria (FimH)
 This protein receptor allows adherence of E. coli to bladder uroepithelial cells,
through attachmet to the mannosylated glycoproteins that line the bladder
mucosa
 The adhesion is common though, so other things must also lead to the bladder
infection
Staph saprophyticus is a gram-positive that is seen in the rest of uncomplicated UTI cases
o S. saprophyticus is seen way more often in the fall
When it becomes acute nonoubstructive pyelonephritis, it is usually E. coli
o Has the adhesion factor P fimbria, which binds Gal disaccharide
 Causes bacterial persistence and inflammation of the urinary tract
o Other virulence factors include aerobactin (scavenges for iron for the bacteria to grow)
and hemolysin (may lyse host cells)
Complicated UTI:
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E. coli is again the most common pathogen for complicated UTI, but the % isn’t as high as for
uncomplicated
Urease producing organisms, like proteus mirabilis, morganella morganii, and providencia spp.
are common causes as well
o These organisms are also pathogenic because as urease metabolizes urea to ammonia, it
can lead to struvite formation
o The ammonia produced damages the kidney directly, and can cause kidney stones that
obstruct and cause further damage
Bacteria from people with complicated UTI are also characterized by being resistant
o This is because of using antibiotics on them in the last time they flared up
People with complicated UTI often have urologic devices in them, like a urethral catheter
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They get coated with biofilm when bacteria contaminate them and grow along them,
then ascend to the bladder
The conditions caused by the device protect the organisms growing from antibiotics and
host defense, making them hard to get rid of
Asymptomatic UTI – E. coli is again most common, with low prevalence of virulence factors
Acute bacterial prostatitis is an uncommon infection, mainly caused by S. aureus or E. coli
Prostate stones form in men with age, providing a way for organisms to persist in the prostate, and a
source of bacteria for relapsing cystitis
The most important host defense for preventing UTI is complete, normal urination
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This removes bacteria in the bladder and along the uroepithelial cells
Host factors in uncomplicated UTI:
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Shows normal voiding
Women with recurrent acute uncomplicated UTI are more likely to have a close relative who
also gets recurrent infections
o Shows a genetic predisposition
o One genetic cause is if you don’t secrete ABH blood antigens
 They’re normally secreted at mucosal surfaces, and bind to receptors on
bacterial cells to prevent attachment to the uroepithelium
 About 1/5 of people are nonsecretors, so their bacterial cell surface receptors
remain exposed, allowing attachment of bacteria to host uroeptihelial cells
The most important behavioral risks for acute cystitis in premenopausal women are sexual
intercourse and use of spermicides for birth control
o Sex mechanically facilitates the ascension of organisms from the periurethral area into
the bladder
o Bacteria enter the bladder in about 1/3 of episodes of intercourse
 They get cleared usually the next time the girl urinates, but if they don’t you get
either symptomatic or asymptomatic infection
o An increased frequency of intercourse is associated with an increased frequency of
symptomatic UTIs
o The normal flora of the vagina maintains an acidic pH that prevents colonization by
potential pathogens like E. coli
 Spermicide disrupts this normal flora, allowing E. coli to colonize the vagina
Other behavioral risk factors that are less important are a new sex partner, diaphragm use, and
recent use of antibiotics
o New sex partner increases exposure to new strains of E. coli
o A diaphragm may block the urethra and prevent complete bladder emptying
Condom use without spermicide, or use of birth control pills, won’t increase risk of infection
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Things that don’t increase risk for UTI are urination before or after sex, wiping, douches and
tampons, types of underwear, or bathing rather than showering
Uncomplicated UTI is rare in healthy young men – so rare though that you basically assume a
UTI in a guy is comlicated
o Risk factors for men include a new sex partner, and anal sex
Patients with complicated UTI have structural or functional problems of the GU tract that compromise
urination, or promote entry of bacteria into the urinary tract
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Includes blocked urine flow, stones, and increased access thanks to catheters or reflux
Women with acute cystitis have an inflammatory response in the urinary tract, characterized by local
cytokine production (like Il-6, 8, or 10) and recruitment of WBCs
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Probably triggered by LPS activating TLR-4 on the bladder epithelium
Untreated acute uncomplicated cystitis resolves in about half of episodes by 2-4 weeks
The limited local immunity that develops in an episode of acute cystitis, doesn’t protect from
future episodes
For acute pyelonephritis, the initial host response is also inflammatory
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Manifested by pyuria (WBCs in the urine) and cytokine production
Systemic inflammotry response includes fever, WBCs, and increased C-reactive protein
o System antibodies develop, mainly IgM for the first infection, and IgG’s in following
infections
The inflammatory response int e kidney likely adds to tissue damage and renal scarring
Diagnosing UTIs:
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Uncomplicated cystitis or pyelonephritis
o Acute cystitis in women presents with lower tract irritative symptoms like dysuria (pain
urinating), frequency (having to go a lot), urgency (need to urinate immediately once
you feel the urge) and suprapubic discomfort
 Some women also get hematuria
 if you see vaginal symptoms like discharge or irritation, consider vaginitis or an
STD
o Women with acute uncomplicated pyelonephritis present with costovertebral angle
pain and tenderness due to renal inflammation
 Usually unilateral, but can be bilateral
 The systemic inflammatory response accompanying pyelonephritis shows fever,
and possibly nausea, vomiting, and sepsis hemodynamic problems
 Pyelonephritis can also show lower-tract irritative symtpoms
Complicated UTI - Show symptoms of uncomplicated or pyelonephritis
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Acute prostatitis presents with severe local and systemic symptoms, including high fever, pelvic
pain, and urinary retention
o Prostate will be swollen and tender
o Don’t do a rectal exam cause it may make things worse
Urine culture
o Need bacteria from urine to diagnose a UTI
o Have men pee in a cup, and women too but they have an increased chance of
contaminating it with vaginal secretions and giving false positive
 If a woman can’t cooperate with urinating, you can get a urine sample with a
catheter
o Contaminants show low #’s of colonies, while infecting organisms will have high
concentrations
o Most people with UTI just have one organism in the urine, but complicated UTI can
show more than one, especially when there’s a device like a catheter in place
o If you took a sample in a way that included biofilm, the biofilm is measured too and
usually has more organisms
o Any pathogens found in the urine is diagnostic for UTI
 For acute pyelonephritis or complicated UTI, they’ll have equal to or more than
105 bacteria
Pyuria is measured by microscopic examination of the urine, or a dipstick leukocyte esterase test
o Usually you’ll see pyuria in UTI, but you usually see WBCs in the urine any time bacteria
is in he urine, so pyuria isn’t diagnostic for UTI
o Lack of pyruia though is a good indictor there is no UTI
Treating UTI’s – page 647 table for treating UTIs
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Antibiotics that get excreted in the urine should be used for therapy
For cystitis, all you need to give them is an antibiotic into the urine
For pyelonephritis, you need antibiotics to get into both the tissues and urine
Short 3 day therapy is done in acute cystitis, and there’s no need for culture tests cause they’ll
take 3 days to get back anyways
Trimethoprim/sulfamethoxazole, or just trimethoprim, are the first choice drugs for 3-day
therapy
o Second line choices include fluoroquiniolone for 3 days or nitrofuantioin for 5 days
o These 3 drugs are empiric therapy
Acute uncomplicated pyelonephritis
o A urine specimen for culture should be taken before starting antibiotics
o The infection can be serious, so you have to know what the infecting organism is, to pick
the right therapy
o Should also take a WBC count, serum creatiine, and blood and urine cultures
o How severe it is depends on if there is fever, and the hemodynamic status
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You start with empiric therapy, and then reassess once urine culture results come back
in 2-3 days
 Can use, trimethoprim/sulfamethoxazole, just trimethoprim fluoroquinolones,
depending on what you think the culture will tell you
o Usually 7-14 days of therapy is recommended
o If there is no improvement in 2-3 days, check for urinary obstruction, abscess, or other
issues
Complicated UTI
o Need a urine sample before you start antibiotics every time
 Due to many different possible infecting organisms, and a good chance of
resistance being present
o If symptoms are mild, delay therapy till the results come back
o If symptoms are severe, empiric therapy is used, and then reassessed once the tests
come back
Asymptomatic bacteiuria – common in many populations, including nursing homes
o Should not be screened or treated in most cases
 Does more harm than good
 Exception – always screen and treat a pregnant patient
 Earlier you catch it, the less the chance of pyelonephritis later int eh
pregnancy
Recurrent UTI- 2 per 6 months, or 3 per year
o Prolonged antibiotic therapy may be indicated, to prevent reinfection
o Recurrent acute uncomplicated UTIs – antibiotics are very effective
 Given as long-term low-dose therapy daily or every other day
 Prophylaxis is indicated after 2 infections
 Trimethoprim/sulfamethoxazole, just trimethoprim, and fluoroquinolones work,
and decrease gram-negative colonizing flora in the gut, vagina,a nd periurethral
area, preventing infection
 Probiotics, like in yogurt, don’t prevent recurrent infections
 Daily cranberry juice or tablets decrease the frequency of infection by 1/3
 The cranberry juice binds E. coli adhesins as it’s excreted
o Recurrent complicated UTI – fix the underlying problem that is promoting infections