AssessmentsLower urinary tract infection
Lower urinary tract infection
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 38-year-old woman comes to the office because of ongoing urinary frequency, urgency, and dysuria. Patient’s medical history includes recurrent urinary tract infections, with about four to six each year for the last three years. She says that her symptoms typically resolve with antibiotic use, but will return once she stops using the antibiotics. Urinalysis is performed and shows the following:
Which of the following is the most likely underlying cause of this patient's recurrent urinary tract infections?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
With cystitis, cyst- refers to the bladder, and -itis refers to inflammation, therefore cystitis describes an inflamed bladder, which is usually the result of a bacterial infection, but also can result from fungal infections, chemical irritants, foreign bodies like kidney stones, as well as trauma.
Now a urinary tract infection, or UTI, is any infection of the urinary tract, which includes the upper portion of the tract—the kidneys and ureters, and the lower portion of the tract—the bladder and urethra.
So cystitis, when it’s caused by an infection, is a type of lower UTI.
Lower UTIs are almost always caused by an ascending infection, where bacteria typically moves from the rectal area to the urethra and then migrate up the urethra and into the bladder.
Having said that, on rare occasions, a descending infection can happen as well where bacteria starts in the blood or lymph and then goes to the kidney and makes its way down to the bladder and urethra.
Normally, urine is sterile, meaning bacteria doesn’t live there; the composition of urine, which has a high urea concentration and low pH, helps keep bacteria from setting up camp.
Also, though, the unidirectional flow in the act of urinating also helps to keep bacteria from invading the urethra and bladder.
Some bacteria, though, are better surviving in and resisting these conditions, and can stick to and colonize the bladder mucosa.
On the other hand, gram positive bacteria can also cause problems, like Enterococcus species, and Staphylococcus saprophyticus, which is actually the second most common cause after E. coli and particularly affects young, sexually active women.
That said, as far as risk factors go, sexual intercourse is a major risk factor, because bacteria can be introduced into the urethra, and this is sometimes even referred to as “honeymoon cystitis”.
In general, women are at higher risk for cystitis than men, due to having a shorter urethra. This is because bacteria that are ascending up the urethra don’t have to travel as far.
Other risk factors include presence of a Foley catheter in the urethra, which can introduce pathogens.
Another risk factor is having diabetes mellitus, since people with diabetes tend to have hyperglycemia or high blood glucose. Normally with an infection, neutrophils move out of the circulatory system toward the infection, called diapedesis, as well as carry out phagocytosis, but hyperglycemia inhibits these processes, making those neutrophils less effective at killing invaders.
Also, infant boys with foreskin around their penis have a slightly higher risk of a UTI compared to infant boys who’ve have had a circumcision.
A final important risk factor is impaired bladder emptying causing urinary stasis, which means urine tends to sit still, allowing bacteria the chance to adhere and colonize in the bladder.