A 67-year-old man complains of urinary obstruction and retention. He is diagnosed with benign prostatic hyperplasia, and urinary bladder catheterization is utilized to temporarily relieve the obstruction. He then undergoes a transurethral resection of his enlarged prostate gland. Following the surgery, an indwelling urinary bladder catheter attached to a closed drainage system is put in place. The patient develops a fever to 38ºC two days later, and on the third postoperative day, he becomes confused and disoriented and has a shaking chill. The patient's vital signs (on the third day) are T = 39 C, P = 120, R = 18, and BP = 90/40 mmHg. On physical examination, he knows his name but is disoriented as to time and place. His heart, lungs, and abdomen are normal, but there is mild costovertebral tenderness over the area of the left kidney.

Question 1.1: What tests would you order to help resolve this case?

A kidney infection may be indicated by left costovertebral angle tenderness, and a UTI seems likely based on the patient's history. A urine sample can be obtained from the catheter port with a needle and syringe. A Gram stain, urinalysis, and urine culture should be carried out on the urine sample. A CBC with differential should also be ordered. Some of the symptoms point to septicemia and shock so blood cultures should be ordered as well.

Lab Results

Laboratory tests showed Hgb 13.5 g/dL, Hct 40.5%, MCV 90 fL, and a white blood cell count of 18,000/µL with differential count of 80 segs, 8 bands, 9 lymphs, and 3 monos. Blood urea nitrogen is 19 mg/dL, serum creatinine 1.0 mg/dL, glucose 81 mg/dL, sodium 140 mmol/L, potassium 4.2 mmol/L, chloride 103 mmol/L, and CO2 26 mmol/L.

The urine sediment contained innumerable white blood cells, a few white blood cell casts, a few red blood cells, and numerous bacteria. The urine Gram-stain showed relatively large, Gram negative bacilli, which were also present in the urine and blood cultures. The urine bacterial count was >105 bacteria/mL. The Gram-negative bacterium isolated from the urine and blood cultures does not have a fermentative metabolism.

Question 1.2: What is your diagnosis?

The presence of white blood cells, red blood cells, and bacteria in the urine sediment indicate a UTI, and the high urine bacterial count confirms this. As noted earlier, the costovertebral angle tenderness hints at kidney involvement, so the UTI probably involves pyelonephritis, an inflammation of the kidney. The elevated temperature is consistent with this, as is the presence of the causative agent in the bloodstream. Pyelonephritis is frequently accompanied by septicemia, although septicemia is not absolutely necessary to produce systemic symptoms such as the fever seen in this case. Given that the infecting bacterium is Gram-negative, it is not surprising that the septicemia would include signs of shock, probably induced by bacterial endotoxin.

Question 1.3: What is the most likely etiology of this infection?

This is obviously a nosocomial infection because it occurred while the patient was being cared for in a hospital. The infection is almost certainly associated with the use of an indwelling urinary catheter. Urinary catheters are actually the most frequent cause of nosocomial infections in the U.S., and the prevalence of UTIs among catheterized patients increases roughly 5% for each day the catheter is left in place. Catheters serve as a conduit along which bacteria can spread. They also serve a source or pathogens that cause persistent infection as long as the catheter remains in place.

Question 1.4: What is the most likely causative agent of this infection?

Escherichia coli is the most frequent cause of uncomplicated UTIs that are not nosocomial in origin. With complicated UTIs (those involving anatomical abnormalities such as obstructions, urinary stones, or indwelling catheters), however, the range of likely causative agents becomes much wider. Pseudomonas aeruginosa is a leading cause of nosocomial UTIs. The most likely alternative causative agents in complicated UTIs are Klebsiella spp. (including K. pneumoniae), Serratia spp., E. coli, and other members of the Enterobacteriaceae. All of these are Gram-negative rods. Pseudomonas tends to produce larger cells than the enteric bacteria, but only an experienced clinical microbiologist could tell the difference with any accuracy.

In this case, the lab reports that the causative agent does not possess a fermentative metabolism. This eliminates the enteric bacteria and makes a diagnosis of Pseudomonas aeruginosa more likely. (Of course, the lab can use various physiological tests to confirm the identities of any of the possible Gram-negative causative agents.)

Question 1.5: How should this patient be treated?

Pyelonephritis generally requires 10-14 days of antibiotic therapy. Treatment for 14-21 days is often recommended in the case of a relapse. It should be noted that, in this type of case, it will be very difficult to cure the infection as long as the obstruction and/or use of the urinary catheter continues. Nosocomial UTIs often are caused by antibiotic-resistant strains because these strains tend to be prevalent in hospitals. In a situation like that described in this case, the hospital has probably been seeing other nosocomial infections caused by the same strain of Pseudomonas. If so, its antibiotic resistance pattern may already be known and the infection in this case should be treated accordingly. In the absence of recent local information, you would initiate treatment with an antibiotic (or combination of antibiotics) known to work well against hospital strains of P. aeruginosa and have the lab do susceptibility testing on the isolated bacterium to make sure you are using an effective treatment regimen.