L32 Enteric infections

Question 1

What is the definition of diarrhea?

Answer 1

Passage of =/> 3 loose or liquid stools per day

Question 2

What is acute and chronic diarrhea?

Answer 2

Acute: <2 weeks
Persistent: > 2 weeks

Question 3

Which of the following is incorrect?
A. Diarrheal stool is stool that is conformed to the shape of the container
B. Gastroenteritis is a syndrome characterised by n/v, diarrhea, abdominal discomfort rather than only diarrhea
C. Food poisoning is a type of gastroenteritis (GE)
D. All GE are caused by food poisoning
E. Dysentry is bloody diarrhea with painful defaecation

Answer 3

D

Question 4

Dysentry is caused by either ________ or _________?

Answer 4

1. Bacterial rods (bacillary)

2. Amobebic (Entamoeba histolytica)

Question 5

Name the 4 groups of causative agents causing gastroenteritis.

Answer 5

1. Bacteria: MC
2. Viruses: rotavirus, norovirus (causing watery diarrhea rather than dysentery)
3. Protozoa: Giardiasis (watery), amoebiasis (dysentery)
4. Non-infective: small bowel malabsorption

Question 6

List 4 host factors pre-disposing to gastroenteriris.

Answer 6

1. Age
2. Immunity (humoral and cell-mediated)
3. GI: normal flora, mucosal integrity, motility
4. Gastric acidity: use of PPI

Others: motility of gut

Question 7

What is the transmission method of gastroenteritis?

Answer 7

1. Fecal-oral route
2. Person-to-person

(waterborne, animal reservoir, sanitation and public hygiene)

Question 8

How is the storage of food related to gastroenteritis?

Answer 8

1. Room temperature without refrigeration at 4 degrees celcius
2. un-preserved food

Question 9

EPEC (enteropathogenic E Coli) main pathogenic mechanism is by mucosal adherence.
Explain the mode of action and clinical presentation.

Answer 9

Effacement of intestinal mucosa;

Presented with moderate watery diarrhea

Question 10

A patient presented with bloody diarrhea. Possible pathogenesis is Mucosal invasion/ cytotoxin.
The mode of action is the penetration and destruction of the mucosa. What are the examples of causative agents?

Answer 10

CHESS mneumonics:

1. Campylobacter jejuni
2. EHEC (Enterohaemorrhagic E coli)
3. Entamoeba histolytica
4. Shigella
5. Salmonella
6. V. parahaemolyticus (vibrio)

Question 11

Exotoxin from ETEC (enterotoxigenic E coli) and V. parahaemolyticus can be heat stable/ heat-labile. What do they mean?

Answer 11

Heat-stable toxin (ST): resist 1000 degrees for 15 minutes, acid resistant, alkali susceptible

Heat-labile toxin (LT): denature at 600 degrees for 15 minutes
(activates adenylate cyclase to increase cAMP in intestinal mucosa)

Question 12

S. aureus, Bacillus cereus, and Clostridium botulinum all work by the production of ________________ that is pre-formed in food, acting directly on ______________, patients presented with _________________.

Answer 12

Neurotoxins/enterotoxins;
CNS/ENS;
Profuse watery diarrhea

Question 13

Other than exotoxin pre-formed in food, ________________ formed in vivo can also cause profuse watery diarrhea causing fluid secretion ___with/without__ mucosal damage.

List 3 causative agents to this type of infection.

Answer 13

Enterotoxins; without;

1. Clostridium perfringens
2. Clostridium botulinum (infants)
3. C. difficile
4. Vibrio cholerae
5. V. parahaemolyticus
6. ETEC (enterotoxigenic E.coli)
7. Bacillus cereus (long incubation)

Question 14

What important history taking information to be noted in patients who complained of diarrhea? (4)

It is also important to examine the hydration status (skin turgor, peripheral and central pulses) and urine output of the patient.

Answer 14

1. Onset
2. Food history
3. TOCC: travel, occupation, cluster, contact
4. Appearance of stool

Question 15

Which of the following about laboratory investigations of diarrhea is correct?
A. Stool can be taken for culture or bacteria or microscopy
B. Blood can be taken for culture
C. Food can be taken for culture routinely
D. Food sample is for the detection of bacteria quantitatively
E. Food sample can detect heat-stable toxins and Enterotoxins

Answer 15

C is incorrect

B. yes, in severe cases
C. no! only in case of an outbreak

D. >10^5 cfu/g (colony forming unit) food (S.aureus, B.cereus), >10^6 cfu/g food (C.perfringes)

Question 16

Which of the following about Stool culture is correct?
A. Bacterial culture: TCBS for Shigella and Salmonella
B. Bacterial culture: DCA (Deoxycholate citrate agar) for Vibrio
C. Skirrow’s agar for Campylobacter
D. Single collection of ova and cysts (parasites) for microscopy
E. Gram stain for Cryptosporidium (parasite)

Answer 16

C is correct

A: Thiosulfate-citrate-bile salts-sucrose agar - VIbrio!

• Yellow: Vibrio cholerae
• Green: Virbio parahaemolyticus

D: requires 3 times! intermittent excretion, amoebae must be examined within 30 minutes after collection
E: Modified acid fast stain for cryptosporidium

Question 17

Stool test:
A. Viral: antigen detection (rotavirus) in infants
B. Viral: PCR (norovirus)
C. Toxin A/B detection by PCR/ELISA in C. difficile colitis

Answer 17

All of the above

Question 18

What is the 1st line treatment for diarrhea? (1)

Briefly describe what is that. (1)

Answer 18

Oral rehydration therapy

• Hypo-osmolar (245nM): low glucose and Na
• improve efficacy in children with acute diarrhea
• may cause biochemical hypoNa without any clinical signs

Question 19

If there is severe dehydration, what is given?

Answer 19

IV fluid

Question 20

The patient presented with early-onset vomiting (<6 hours) after ingestion of food (neurotoxins) as well as delayed onset of diarrhea (enterotoxins).
Possible agent?

Answer 20

Bacillus cereus

Question 21

The patient has consumed defectively-canned food and presented with descending flaccid paralysis.
What is the causative agents and specific treatment? (2)

Answer 21

Clostridium botulinum
Tx: Antitoxins

• neurotoxins at NMJ causing descending flaccid paralysis and respiratory arrest
• toxins are pre-formed in adult, formed in vivo in infants

Question 22

E coli O157:H7 can cause _________________, thus _________ is contraindicated as it increases lysis of bacteria, increases Shiga-like toxin and aggrevate the above situation.

Answer 22

HUS - Hemolytic uremic syndrome

antibiotics

Question 23

The patient has taken re-heated and pre-cooked meat dishes and has a relatively late onset of diarrhea (compared to those with pre-formed neurotoxins: 8-12 hours).
Possible agent?

Answer 23

Clostridium perifringens.

Question 24

This agent can be found in undercooked poultry (animal reservoir) and has varying mechanisms of infection - enterotoxin, cytotoxic, and invasive.
Name this agent and what can be given if there is systemic involvement (e.g. fever) as a treatment? (2)

Answer 24

Salmonella enteritidis;

Quinolones

(inflammatory diarrhoea: 2nd most common after Campylobacter - Sketchy)

Salmonella typhi - another type causing Typhoid/Enteric fever

Salmonella is the most common causal agent of osteomyelitis in sickle cell disease patients

Question 25

_______________ is the MC cause of diarrhea in western world, found in undercooked poultry. It also causes reactive arthritis and neurological complications. What can be given as treatment?

Answer 25

Campylobacter jejuni/coli; | usually self-limiting but Erythromycin (macrolide)/ Quinolones to reduce the duration of symptoms

Question 26

This patient experienced explosive diarrhea after consuming contaminated seafood (halophilic - salt-loving bacteria). This bacteria produces enterotoxins and cytotoxins. Name the possible agent.

Answer 26

Vibrio parahaemolyticus

Question 27

Traveler's diarrhea has risk highest in areas with poor food and water hygiene. What are the commonest causative organisms (2).

Answer 27

1. ETEC (enterotoxigenic) E.coli (Bacerial) | 2. Giardia lamblia (Parasitic)

Question 28

How is Traveler's diarrhea prevented? (1) | Treatment (2)

Answer 28

Prevention: Cook it, peel it, or leave it Treatment - Oral rehydration - Quinolones if dysenteric of fever, but resistance common

Question 29

Clostridium difficile-associated disease (CDAD) is found in 3% of colonic flora of a healthy population. Which of the following are risk factors of it? A. Advanced age B. Immunocompromised C. GI surgery D. Prolonged hospitalization

Answer 29

all of the above

Question 30

What is the pathogenesis of Clostridium difficile-associated disease (CDAD)? It spreads via ________________route as vegetative form/hard spores. When antibiotics like clindamycin is given, there is the destruction of colonic normal flora. C. difficile then? (2)

Answer 30

Fecal oral route; - reproduces in intestinal crypts, - releasing toxins A (recruit neutrophils) and B (degrade colon epithelial cells)

Question 31

What are the possible presentations of Clostridium difficile-associated disease (CDAD)?

Answer 31

1. Watery diarrhea 2. Toxic megacolon 3. Pseudomembranous colitis (PMC): yellowish plaques - a pseudomembrane of necrotic epithelial cells, mucus, fibrin and neutrophils adhering to colonic mucosal surface 4. Colon perforation and sepsis

Question 32

How can Clostridium difficile-associated disease (CDAD) be diagnosed?

Answer 32

Detection of Toxins A and B in stool by PCR, ELISA

Question 33

Treatment of Clostridium difficile-associated disease (CDAD)?

Answer 33

1. Discontinue antibiotics (+PPI) if possible 2. Antibiotics treatment a. Oral metronidazole 500mg Q8h 10-14 days b. Oral vancomycin 125-500mg Q6h - IV metronidazole and IV vancomycin is INEFFECTIVE 3. Surgery - Relapse common >50% - Mx: tapering course of vancomycin over few weeks, or donor faecal transplant

Question 34

Prevention of Clostridium difficile-associated disease (CDAD)? (3)

Answer 34

Personal hygiene - contact precaution - handwashing, gowns, gloves, decontamination Food hygiene - avoid uncooked meat and seafood - refrigeration and preservation Environmental hygiene - clean water hygiene (also avoid overprescribing antibiotics - nosocomial! - Clindamycin, cephalosporins, amoxicillin, ampicillin caused)