A 20-year-old woman attending FSU experiences increasing urinary frequency, along with urgency and dysuria for 2 days. Over the next 12 hours or so, these symptoms persist and her urine is pink or bloody. She then becomes concerned and goes to the campus student health clinic for advice. Vital signs are: T = 37.5ºC, P = 105, R = 18, and BP = 105/70 mm Hg. The only abnormal finding on physical examination is a mild tenderness to deep palpation in the suprapubic area. No genital ulcers are noted. There is no vaginal discharge. The patient has no previous history of similar complaints. However, she has recently become sexually active and has been using a diaphragm with spermicide.

Question 1.1: What is your preliminary diagnosis and what tests should you carry out to confirm it?

The patient's history might indicate a sexually transmitted disease. However, she does not have any signs or symptoms (e.g., genital lesions or purulent discharge) that might specifically point to one of the common STDs. The primary symptoms of dysuria, frequency, and urgency would appear to indicate a UTI. In the absence of significant fever and flank pain (which might indicate pyelonephritis), it is most likely cystitis (inflammation of the bladder), a lower UTI.

The appropriate lab tests to confirm this diagnosis would include a urinalysis with microscopic evaluation of clean-catch urine for bacteria and pyuria. A urine culture and CBC are not indicated for a first incident with no fever and with no evidence for pyelonephritis, diabetes, or other complications. These tests will not change the outcome and are not cost effective.

Test Results

Laboratory tests including CBC (had they been done) would show Hgb 13.9 g/dL, Hct 41.7%, MCV 79 fL, and white blood cell count of 10,500/µl with 66% segs, 5% bands, 19% lymphs, 9% monos, and 1% eos. Blood urea nitrogen is 15 mg/dL, serum creatinine 0.8 mg/dL, glucose 74 mg/dL, sodium 141 mmol/L, potassium 3.9 mmol/L, chloride 101 mmol/L, and CO2 25 mmol/L.

The urine sediment contains innumerable white cells, moderate numbers of red cells, and noticeable bacteria. A urine culture grows 103 bacterial cells/ml. A Gram stain of the urine reveals a few Gram-negative rods, and the urine culture grows Gram-negative rods.

Question 1.2: What is your final diagnosis and what is the most likely causative agent?

The lab tests confirm a diagnosis of cystitis. The urine bacterial plate count may appear negative in that growth of more than 105 organisms/ml from a "clean-catch" sample is usually considered to indicate infection. In patients with noticeable symptoms, however, 102 to 104 organisms/ml is often sufficient to indicate infection, and the count obtained from this patient is within that range. Also, the specimen does not appear to be contaminated by multiple organisms.

A variety of bacteria can cause cystitis, but 80% of the cases seen in patients without structural abnormalities (obstructions, urinary stones, indwelling urinary catheters, etc.) and with a history that eliminates nosocomial infection are caused by Escherichia coli. The most likely alternative causative agents are other types of enteric bacteria (Enterobacteriaceae spp.), Proteus mirabilis, Staphylococcus saprophyticus (the incidence of which is increasing in young women), enterococci, and Group B streptococci. It is not possible to distinguish between E. coli, other enteric bacteria, and P. mirabilis with a Gram stain because they are all Gram-negative rods that look roughly the same. Additional lab tests based on physiological or biochemical traits are required to confirm the specific identities of these organisms. This is also true for the different types of Gram positive cocci listed above.

Question 1.3: How do infections like the one seen in this patient usually get started?

Most uncomplicated lower UTIs are caused by fecal bacteria that are inadvertently introduced into the periurethral area. The bacteria then gain access to the urinary bladder by ascent from the urethra. Transport to and subsequent establishment within the bladder is facilitated by various predisposing factors (see answer to next question). Hematogenous infection of the urinary tract is quite rare and is more likely to lead to renal abscesses than to lower UTIs.

Question 1.4: What predisposing factors did this patient have for this type of infection?

Women are generally far more susceptible than men to lower UTIs for several reasons. The female urethra appears to be particularly prone to colonization with colonic Gram-negative bacilli because of its proximity to the anus. The comparatively short length of the female urethra also facilitates transport of bacteria from the periurethral area to the bladder. The incidence of UTIs in young women increases markedly with the onset of sexual activity. (Note the history of the patient in this case.) Apparently, sexual intercourse mechanically introduces urethra associated bacteria upward into the bladder. As a result, voiding shortly after intercourse helps to reduce the risk of cystitis. The use of a contraceptive diaphragm interferes with complete emptying of the bladder. Urine retained in the bladder encourages the growth of bacteria therein and greatly promotes infection.

Question 1.5: What are the human body's natural defenses against infections like this one?

The most important antimicrobial defenses in the urinary tract are the periodic outward flow of urine and the sloughing of epithelial cells to which bacteria may attach. The bladder transitional epithelium produces a mucoid secretion with natural anti-bacterial properties. In males, antimicrobial substances in prostatic fluid may provide additional protection. Immune defense mechanisms do little to protect against infection in this part of the human body. Therefore, anything that interferes with normal voiding of urine (e.g., obstructions, physiological malfunctions, or the use of contraceptive diaphragms, etc.) greatly increases the likelihood of infection.

Question 1.6: How should this infection be treated?

A single dose or short course of appropriate antibiotic is usually sufficient to treat uncomplicated bacterial cystitis. This will not be effective in patients who have early pyelonephritis, chlamydial cystitis, or an infection caused by a resistant strain. The current drugs of choice for infections by Escherichia coli, Staphylococcus saprophyticus, Proteus mirabilis, or Klebsiella include trimethoprim, trimethoprim-sulfamethoxazole, or a quinolone.