Practice questions answers 1 Infectious gastroenteritis
Practice questions answers 1
Infectious gastroenteritis
© Jun Wang, MD, PhD
1. D. The symptoms described in the case, including mild to moderate mid-abdominal cramps, nausea, vomiting, and watery diarrhea after attending a social gathering at a seafood restaurant, are suggestive of a foodborne illness. Although many pathogens may cause diarrhea, the mild presentations are most likely associated with norovirus infection. The major pathogenetic pathway for norovirus induced diarrhea is malabsorption. Activation of guanylate cyclase and efflux of Cl– and H2O is seen in enterotoxigenic e coli diarrhea and cholera. However, enterotoxigenic e coli usually do not have vomiting. Cholera usually presents with severe diarrhea with rice water appearance and signs of dehydration. While colonization of giardia intestinalis can be seen in duodenum and jejunum, they do not invade mucosa. Suppression of normal colonic flora is associated with clostridium difficile diarrhea, characterized by green foul smelling watery diarrhea, after usage of antibiotics. In addition, patients with clostridium difficile diarrhea usually have fever and are more severely ill.
2. C. For mild diarrhea without severe illness, multi-pathogen molecular tests can be used for a quick evaluation of possible pathogens, even though most of the diagnosis can be made clinically. Colonoscopic examination and biopsy are not commonly used for diagnosing Infectious gastroenteritis, although they can be used for clostridium difficile induced pseudomembranous colitis. Darkfield microscopic examination of stool can be used to identify highly motile comma-shaped bacteria of vibrio cholerae. Regular microscopic examination of stool can be used to identify cysts and trophozoites for parasite infection, such as giardia intestinalis and entamoeba histolytica. Stool culture is commonly used for confirmation of pathogens causing bacterial gastroenteritis. However, stool microbiology tests, including culture, are usually not recommended unless presence of fever, bloody/inflammatory diarrhea, severe diarrhea/hypovolemia, or high risk comorbidities etc.
3. E. See discussion in question 1. Campylobacter infection is characterized by fever, abdominal pain and inflammatory diarrhea. Shigella infection usually has fever and multiple scanty bloody diarrhea and tenesmus.
4. A. Watery diarrhea with the recent travel history to a developing country and consumption of street food, is highly suggestive of a enterotoxigenic e coli infection, especially when vomiting is not present. Enterotoxigenic e coli causes diarrhea due to production of enterotoxin ST to activate guanylate cyclase and enterotoxin LT to cause efflux of Cl– and H2O by activating adenylate cyclase. While colonization of giardia intestinalis can be seen in duodenum and jejunum, they do not invade mucosa. Malabsorption caused by norovirus and giardia intestinalis can result in diarrhea. Suppression of normal colonic flora is associated with clostridium difficile diarrhea, characterized by green foul smelling watery diarrhea, after usage of antibiotics.
5. C. Molecular tests for enterotoxin LT can be used for quick diagnosing enterotoxigenic e coli infection. Also see discussion of question 2.
6. B. Watery diarrhea with the recent travel history to a developing country and consumption of street food, is highly suggestive of an enterotoxigenic e coli infection, especially when vomiting is not present. Salmonella enterocolitis is characterized by fever, vomiting and watery to bloody diarrhea. Shigella infection usually has fever and multiple scanty bloody diarrhea and tenesmus.
Also see discussion of question 1.
7. E. This case is characterized by bloody diarrhea after traveling to a developing country, accompanied with fever and abdominal cramps. Stool findings of inflammatory diarrhea and multiplex molecular panels finding of bacterial pathogens are consistent with bacterial gastroenteritis. Stool culture is commonly used for confirmation of pathogens, especially when molecular tests are positive for bacterial infections. Clostridium difficile test is used for clostridium difficile diarrhea, characterized by green foul smelling watery diarrhea, after usage of antibiotics. Molecular tests for enterotoxin LT can be used for quick diagnosing enterotoxigenic e coli infection. Also see discussion of question 2.
8. C. Results of stool culture at 37°C of Gram-negative bacilli, forming dark pink colonies on MacConkey agar is consistent with sorbitol fermenting e coli infection, include enterotoxigenic e coli and enteroinvasive e coli, but not enterohemorrhagic e coli infection. EHEC does not ferment sorbitol and will have white colonies on MacConkey agar. While bloody diarrhea can be caused by enterohemorrhagic e coli or enteroinvasive e coli, enterotoxigenic e coli usually cause watery diarrhea with fever. Clostridium difficile is Gram-positive and usually cause green foul smelling watery diarrhea, after usage of antibiotics. Campylobacter infection is characterized by fever, abdominal pain and inflammatory diarrhea. However, campylobacter need to be cultured in Campylobacter or Skirrow agar at 42.0°C. Shigella infection usually has fever and multiple scanty bloody diarrhea and tenesmus. Shiga toxin test is positive for infections of Shigella or enterohemorrhagic e coli. Cholera usually presents with severe diarrhea with rice water appearance and signs of dehydration.
9. D. Enteroinvasive e coli cause diarrhea by direct invasion and subsequent inflammation of colonic mucosa. After invasion of colonic epithelium, they will proliferate intracellularly and spread laterally through actin jet trail. Intestinal endothelial injury may be cause by Shiga toxin produced by Shigella or enterohemorrhagic e coli. Also see discussion of question 1.
10. E. See discussion of questions 2 and 5.
11. C. See discussion of question 8.
12. C. See discussion of questions 1 and 9.
13. E. Shiga toxin can be produced by Shigella or enterohemorrhagic e coli, and is the cause of HUS. Clostridium difficile test is used for clostridium difficile diarrhea, characterized by green foul smelling watery diarrhea, after usage of antibiotics. Molecular tests for enterotoxin LT can be used for quick diagnosing enterotoxigenic e coli infection. Also see discussion of question 2.
14. E. See discussion of questions 2 and 7.
15. A. The clinical presentation of fever, abdominal pain and diarrhea from watery to bloody, after poultry consuming is highly suspicious of campylobacter infection. This infection is confirmed by findings of Gram-negative curved rods by stool culture on Skirrow agar at 42.0°C. Other pathogenic e coli and Shigella will grow on MacConkey agar at 37.0°C. Vibrio cholerae will grow on thiosulfate citrate bile sucrose agar or taurocholate tellurite gelatin agar.
16. C. Campylobacter causes diarrhea by invasion and subsequent inflammation of intestinal mucosa. Activation of guanylate cyclase and efflux of Cl– and H2O is seen in enterotoxigenic e coli diarrhea and cholera. Intestinal endothelial injury can be seen in HUS, caused by Shaga toxin produced by Shigella or enterohemorrhagic e coli. Malabsorption is the major cause of diarrhea associated with norovirus and giardia intestinalis.
17. A. Campylobacter is sensitive to gastric acid, and more likely cause symptomatic infections in patients with reduced gastric acid production, such as autoimmune gastritis. Other comorbidities in this patient do not have any known connection with increase risk for infectious gastroenteritis.
18. C. This case is characterized by severe watery diarrhea after traveling to a developing area and consuming likely contaminated street food. The elevated hematocrit and low serum bicarbonate are consistent with severe dehydration and metabolic acidosis. The watery, milky stool with abundant whitish mucus-like contents is also called “rice water” diarrhea, a typical presentation of cholera. Darkfield microscopic examination of stool can be used to identify highly motile comma-shaped bacteria of vibrio cholerae. Clostridium difficile test is used for clostridium difficile diarrhea, characterized by green foul smelling watery diarrhea, after usage of antibiotics. Molecular tests for enterotoxin LT can be used for quick diagnosing enterotoxigenic e coli infection. Shiga toxin can be produced by Shigella or enterohemorrhagic e coli, and is the cause of HUS. Diarrhea caused by Shigella or enterohemorrhagic e coli is usually bloody, not watery.
19. F. See discussion of question 18. Diarrhea caused by campylobacter, Shigella and entamoeba histolytica are usually bloody. Diarrhea caused by enterotoxigenic e coli can be watery, but usually do not have motile, comma-shaped organisms in stool. Diarrhea caused by giardia intestinalis is usually fatty with foul odor. The watery diarrhea associated with enterotoxigenic e coli, giardia intestinalis or norovirus usually does not have abundant mucus in the stool, nor severe dehydration, as seen in cholera.
20. A. Activation of guanylate cyclase and efflux of Cl– and H2O is seen in enterotoxigenic e coli diarrhea and cholera. Inflammation of colonic mucosa can be caused by infection of Shigella, enterohemorrhagic e coli, entamoeba histolytica, campylobacter, etc. Inhibition of ribosome function and endothelial injury are commonly due to Shiga toxin produced by Shigella or enterohemorrhagic e coli. Malabsorption is the major cause of diarrhea associated with norovirus and giardia intestinalis.
21. D. The clinical presentation and laboratory findings of microangiopathic hemolytic anemia (as evidenced by fragmented red cells on peripheral blood smear), thrombocytopenia, and acute kidney injury are consistent with hemolytic-uremic syndrome (HUS), a condition often associated with enterohemorrhagic e coli, commonly serotype O157:H7, or Shigella. Both infections may have very similar presentations concerning diarrhea. However, enterohemorrhagic e coli is much more commonly seen and tend to have a low grade fever, unlikely Shigella infection, usually cause a fever greater than 101°F. Other pathogens have no known association with HUS.
22. B. The consumption of unpasteurized milk from a local farm is most likely associated with enterohemorrhagic e coli infection. Poultry consumption is more commonly associated with salmonella. Rice is commonly associated with B. cereus. Sea food is more commonly associated with norovirus and cholera. Contaminated water is commonly associated with Shigella, enterotoxigenic e coli diarrhea and cholera.
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