A 72-year-old man is brought to the emergency department from a skilled nursing facility due to altered mental status, skin flushing, and a high fever. His temperature is 38.9 C (102 F), blood pressure is 80/40 mm Hg, pulse is 120/min, and respirations are 26/min. If blood cultures are positive for Escherichia coli, which of the following is the most likely site of infection leading to bacteremia in this patient?

Question

A 72-year-old man is brought to the emergency department from a skilled nursing facility due to altered mental status, skin flushing, and a high fever.  His temperature is 38.9 C (102 F), blood pressure is 80/40 mm Hg, pulse is 120/min, and respirations are 26/min.  If blood cultures are positive for Escherichia coli, which of the following is the most likely site of infection leading to bacteremia in this patient?

Quizplus · Accepted Answer

This elderly patient with fever, hypotension, altered mental status, and Escherichia coli bacteremia has septic shock most likely due to urinary tract infection (UTI). UTIs are a common cause of sudden disorientation or confusion in the elderly. Predisposing factors include urinary obstruction (eg, benign prostatic hypertrophy), fecal incontinence, neurogenic bladder (eg, due to diabetes), and frequent or indwelling catheterization. E coli is the most common organism causing UTI (others are Proteus, Klebsiella, Enterobacter, Citrobacter, and Pseudomonas), and UTIs represent the most common cause of E coli bacteremia. E coli is part of the normal gastrointestinal (GI) flora. Some strains have adhesive fimbriae allowing them to potentially contaminate the urethra and ascend the urinary tract, leading to UTI or pyelonephritis. Gram-negative sepsis or septic shock can ensue as a result of the body's systemic reaction to lipopolysaccharide endotoxin (a component in some gram-negative bacterial membranes). Signs of sepsis include hyper- or hypothermia, tachycardia, tachypnea (can lead to respiratory alkalosis), and leukocytosis. Severe sepsis is marked by organ dysfunction due to poor blood flow (eg, oliguria from poor renal perfusion and altered mental status from poor cerebral perfusion). Metabolic lactic acidosis can be seen, particularly during the late stages, due to poor tissue perfusion. Treatment is focused on maintaining blood pressure and organ perfusion with intravenous fluids, administering antibiotics directed against the offending organism, and maintaining proper ventilation and oxygenation. (Choice A) The biliary tree has many protective mechanisms against bacterial colonization and infection. The sphincter of Oddi prevents reflux of nonsterile duodenal contents into the biliary tree, bile salts can inhibit bacterial growth, downstream biliary flow helps to wash organisms away from the biliary tree, and bile secretory IgA helps to prevent bacterial adherence. Despite this, organisms such as E coli, Klebsiella, Enterobacter, and enterococci occasionally infect the biliary tract, leading to cholangitis that can cause sepsis if left untreated. However, this process is a much less frequent cause of bacteremia than UTI, and cholangitis classically presents with fever, abdominal pain, and jaundice. (Choices B and F) Many microorganisms inhabit the human GI tract as normal flora. Under normal circumstances, small intestine bacteria do not cause systemic disease. Anaerobic or gram-negative rod bacteremia can result from colonic perforation due to surgery, trauma, or wall rupture from certain pathologic processes. However, the likely site of infection in this patient with E coli bacteremia is the genitourinary tract; although it may represent the ultimate site of origin of E coli, the GI tract is not typically a site of infection. (Choices C and D) Bacterial causes of upper respiratory tract infection (eg, Moraxella and Haemophilus) do not usually cause disseminated disease. E coli and other gram-negative rods (Pseudomonas, Acinetobacter, and Klebsiella) would be common causes of health care-acquired pneumonia in this nursing home resident; from the lungs, these organisms can easily gain access to the bloodstream and cause sepsis. However, this patient does not have any respiratory symptoms, and E coli sepsis is more commonly due to UTI than pneumonia. (Choice E) Normal skin flora includes mostly gram-positive organisms such as staphylococci and streptococci. Educational objective: Escherichia coli is the most common cause of urinary tract infection (UTI) in both healthy adults and elderly patients. E coli is a part of the normal gastrointestinal flora, and special adhesive proteins (fimbriae) allow some strains to colonize and ascend the urinary tract. This can result in UTI, pyelonephritis, or bacteremia and sepsis following access to the bloodstream. UTIs are the most common cause of E coli bacteremia.

A 72-Year-Old Man Is Brought to the Emergency Department from a Skilled