A 42-year-old man comes to the office due to 2 weeks of progressive fever, chills, abdominal discomfort, and loose stools, which began during a trip to Southeast Asia. He received no pre-travel vaccinations and did not strictly follow food and water safety precautions during the trip. The patient has no chronic medical conditions but has experienced a prior episode of Salmonella enteritidis gastroenteritis, which resolved with symptomatic care. Temperature is 39.4 C (103 F), blood pressure is 110/64 mm Hg, pulse is 62/min, and respirations are 18/min. Physical examination reveals a faint macular rash on the trunk. There is mild tenderness on palpation of lower abdominal quadrants with no guarding or rebound tenderness. Blood culture grows non-lactose fermenting gram-negative rods. Which of the following best explains the prolonged and severe disease course from this pathogen compared to the patient's previous bacterial infection?

Question

A 42-year-old man comes to the office due to 2 weeks of progressive fever, chills, abdominal discomfort, and loose stools, which began during a trip to Southeast Asia.  He received no pre-travel vaccinations and did not strictly follow food and water safety precautions during the trip.  The patient has no chronic medical conditions but has experienced a prior episode of Salmonella enteritidis gastroenteritis, which resolved with symptomatic care.  Temperature is 39.4 C (103 F), blood pressure is 110/64 mm Hg, pulse is 62/min, and respirations are 18/min.  Physical examination reveals a faint macular rash on the trunk.  There is mild tenderness on palpation of lower abdominal quadrants with no guarding or rebound tenderness.  Blood culture grows non-lactose fermenting gram-negative rods.  Which of the following best explains the prolonged and severe disease course from this pathogen compared to the patient's previous bacterial infection?

Quizplus · Accepted Answer

11ec160b_3855_c8b5_9249_2dabb99a0952_MD0001_00 Salmonella are gram-negative, non-lactose-fermenting, motile enteric rods that are divided into nontyphoidal (eg, S enteritidis) and typhoidal (eg, S typhi, S paratyphi) strains. Both strains are able to cause disease by penetrating enterocytes, where they then travel in vacuoles from the apical to the basolateral end of the cell to invade the lamina propria. However, the pathogenesis then diverges, as follows: Nontyphoidal species are phagocytosed by neutrophils and macrophages in the lamina propria and induce a massive inflammatory response marked by dramatic neutrophil infiltration. The cytokine-mediated inflammatory response typically results in 1-5 days of gastroenteritis (eg, watery diarrhea, abdominal pain, and fever). Most cases resolve without intervention. In contrast, typhoidal species contain a specialized capsular antigen called Vi (short for virulence) that inhibits neutrophil recruitment and phagocytosis. This limits the acute inflammatory response that helps contain the nontyphoidal species. It also inhibits macrophages from generating an oxidative burst to destroy the bacteria, which allows the pathogen to undergo extensive unchecked intracellular replication and subsequently disseminate through the lymphatic and reticuloendothelial system. This results in typhoid fever. Typhoidal strains of Salmonella are found only in humans and are typically transmitted by the consumption of food or water contaminated by human feces. Typhoid Salmonella is endemic to areas where sanitation is poor. Travelers may become ill if they are unvaccinated (typhoid vaccine) and do not strictly adhere to food and water safety precautions. Manifestations begin approximately a week after transmission with an escalating fever that is often associated with relative bradycardia (pulse-temperature dissociation). Approximately a week later, patients typically develop abdominal pain, diarrhea or constipation, and transient salmon-colored macules (rose spots) on the trunk. Serious complications such as intestinal bleeding and perforation can occur later. (Choice A) Contact between Entamoeba histolytica and the host cell results in the insertion of an amebic channel-forming protein in the host cell membrane that causes cell death. Manifestations of E histolytica infection typically include bloody diarrhea (colitis) and/or extraintestinal manifestations (eg, liver abscess). (Choice B) Campylobacter infection is a common cause of self-limited acute infectious diarrhea and may result in the formation of cross-reacting antibodies to GM1 ganglioside, leading to Guillain-Barré syndrome. Campylobacter symptoms usually last <7 days and do not include rose spots or temperature dissociation. (Choice D) Shigella and enterohemorrhagic Escherichia coli produce a potent exotoxin that can result in cell death, hemorrhagic colitis, and systemic manifestations (eg, hemolytic-uremic syndrome). Exotoxins do not play a prominent role in Salmonella infection. (Choice E) Rotavirus and giardia damage intestinal villi, which leads to intestinal malabsorption due to villous blunting and decreased levels of brush border enzymes (eg, maltase, sucrase, lactase). Educational objective: Typhoid strains of Salmonella contain a capsular antigen (Vi) that inhibits neutrophil phagocytosis, neutrophil recruitment, and macrophage-mediated destruction. Therefore, typhoid strains are able to undergo extensive replication within the intracellular space of macrophages with subsequent spread through the lymphatic and reticuloendothelial system, leading to a widespread systemic disease (typhoid fever).

A 42-Year-Old Man Comes to the Office Due to 2