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Urinary tract infections: Clinical practice

Urinary tract infections: Clinical practice


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USMLE® Step 2 style questions USMLE

18 questions

A 35-year-old man comes to clinic because of hematuria for the past week. He says red streaks of blood appear during the last 2 seconds of urination. Past medical history is noncontributory. He does not take any medications and denies alcohol, tobacco, or illicit drug use. His spouse mentions that he went on a trip to North Africa 8 months ago and since then he has had diarrhea about 3 days per week. His temperature is 37.2° C (99° F), pulse is 77/min, respirations are 16/min, and blood pressure is 130/70 mm Hg. A bladder biopsy shows pink, polygonal cells with hyperchromatic nuclei having intermediate filament. Which of the following mechanisms of treatment would have most likely prevented this exacerbation of his condition?


Content Reviewers:

Rishi Desai, MD, MPH

Urinary tract infections or UTIs are infections that affect part of the urinary tract.

They’re usually caused by bacteria found in fecal flora, which normally colonizes the urethral meatus.

However, when those bacteria make their way up the urethra and into the bladder, they can cause lower UTIs, like cystitis, which is the inflammation of the bladder, or upper UTIs, like acute pyelonephritis, which is the inflammation of the renal pelvis and kidneys.

Both cystitis and acute pyelonephritis can be uncomplicated or complicated.

By complicated, we mean that the individual has an associated structural or functional condition of the genitourinary tract or an underlying disease which increases the risk of a severe infection.

So a complicated UTI is one that happens in a male, a pregnant female, and individuals with indwelling urinary catheters.

Additionally, it’s considered a complicated UTI when it happens in individuals with poorly controlled diabetes mellitus, immunocompromised individuals, those with urologic conditions- like urethral strictures, and those that have had urologic procedures.

So let’s start with uncomplicated cystitis.

The most common pathogens are Enterobacteriaceae which include Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis.

Another pathogen is Staphylococcus saprophyticus.

Uncomplicated cystitis usually appears in women, because they have a shorter urethra than men, making the urethral meatus closer to the anal orifice.

Risk factors for cystitis are recent sexual intercourse, as well as the use of spermicide-coated condoms, or general spermicides- because spermicides facilitate the growth of E.coli.

Shortly after a sexual intercourse, symptoms include dysuria, urinary frequency, urinary urgency, and suprapubic pain. In females over 65 years, symptoms can include chronic dysuria or urinary incontinence.

Now, in young women with typical symptoms, no further testing is necessary to make the diagnosis.

But in individuals with atypical symptoms, a urinalysis is done, either by dipstick or microscopy, along with urine cultures and susceptibility testing.

On the dipstick, a positive leukocyte esterase- suggests pyuria, and positive nitrites- reflects the presence of Enterobacteriaceae, which convert urinary nitrate into nitrite.

On microscopy, there are usually over 10 leukocytes per microliter, and over 5 red blood cells per microliter.

A gram stain is also done in order to rapidly identify some bacteria, like E.coli.

Now, ideally the urine sample shows the bladder bacterial count with very little contamination from the distal urethra and genital mucosa.

This is obtained by a clean-catch, mid-stream sample of the first urine of the day.

In cystitis, the urine culture shows bacteriuria, meaning more than 1000 or 10 to the third power colony-forming units or CFUs per milliliter of the predominant species- usually a known pathogen.

If it’s lower than 1000 CFU per milliliter, then it’s considered contamination.

A similar cutoff is used for a urine sample taken from an individual with an indwelling urinary catheter.

If the urine sample was taken through suprapubic aspiration, then any amount of bacteria present- no matter the number- it’s considered diagnostic for an infection. That’s because the urine in the bladder is normally sterile and shouldn’t contain any bacteria.

Treatment of uncomplicated cystitis relies on antibiotics, and medication to help with urinary discomfort.

Antibiotic therapy is usually done empirically without urine culture and susceptibility testing, and common choices are 100 milligrams of Nitrofurantoin twice daily for 5 days or a single double strength of Trimethoprim-sulfamethoxazole tablet, or 160 mg of Trimethoprim and 800 mg of sulfamethoxazole twice daily for 3 days, both give orally.

Alternatively, 3 grams of fosfomycin can be given orally in a single dose.

Follow-up cultures are not needed if symptoms resolve on antibiotic therapy.

However, if individuals have persistent symptoms after 72 hours of antibiotics or recurrent symptoms within a few weeks of the initial treatment, then urine cultures and susceptibility testing is done and empiric treatment is started with another antibiotic.

When results are available, antibiotic treatment is adjusted accordingly.

Pain management is done with phenazopyridine for 3 days- this is a drug that’s excreted in the urine and has a local analgesic effect - which helps relieve dysuria.

Moving on to uncomplicated pyelonephritis, which is typically caused by the ascension of bacteria via the urethra and into the bladder, ureter and the kidneys, but can also be caused by bacteremia causing an infection in the kidneys.

Symptoms develop quickly and the individual typically has a fever, costovertebral angle tenderness, nausea, and vomiting, in addition to symptoms of cystitis.

Lab studies include a CBC which typically shows leukocytosis with neutrophilia.

Renal function can be checked by obtaining a BUN and creatinine level.

Urinalysis is done using either with dipstick or microscopy.

On microscopy, if there are white cell casts that take the form of the renal tubules, then it suggests that there’s a renal origin for pyuria.

That’s because where there’s an infection in the renal pelvis- there are also leukocytes and they tend to aggregate and take the form of the renal tubules as they pass through.

Finally, urine culture and susceptibility testing is always done.

On a renal ultrasound, pyelonephritis shows up as a hypoechoic mass within one kidney, but it can also be bilateral.

Now, sometimes imaging is needed with an abdominal CT-scan with or without contrast.

For example, imaging is useful in individuals who still have symptoms after 72 hours of antibiotic treatment.

On a CT-scan, acute pyelonephritis shows localized hypodense regions in one or both kidneys.

Imaging should also be done if we suspect a urinary obstruction-like a stone- which can cause a decline in urine output and cause elevated creatinine levels.

A CT-scan can help identify a stone’s location as well as signs of hydronephrosis- which often happens as a result of the obstruction.

Okay, now, empiric treatment can be started with oral ciprofloxacin for 7 days in individuals that can tolerate oral treatment.

In individuals with nausea or vomiting, IV ciprofloxacin or IV ceftriaxone can be used for 10 to 14 days.

IV antibiotics can be switched to oral antibiotics if symptoms improve.

In individuals with urinary obstruction, broad spectrum antibiotics like IV Imipenem plus IV Vancomycin are given for about 14 days.

The antibiotic treatment is then adjusted according to the results of urine culture and susceptibility testing.

Now, let’s switch to complicated UTIs.

In both complicated cystitis or complicated pyelonephritis, a urinalysis, urine culture, and susceptibility testing is always done, because the pathogen is more likely to be an atypical bacteria.