MB9 Gastrointestinal Infections 1

Question 1

What are the body’s natural barriers to infection?

Answer 1

Question 2

1. What is Diarrhoea?
2. Where is it particularly prevalent?
3. How is it diagnosed?
4. What types of organisms can cause it?

Answer 2

1. Mild & self-limiting to severe with dehydration & death
2. A leading cause in childhood death in the developing world
3. Microbiologic diagnosis is impossible without laboratory investigations
4. Bacteria, Viruses and Parasites

Question 3

How are these different causes of diarrhoea diagnosed?

1. Bacteria
2. Viruses
3. Parasites

Answer 3

1. Culture (Increasingly PCR is replacing this), Toxin Detection
2. Electron Microscopy, PCR
3. Light Microscopy

(all from faeces)

Question 4

In general, how are diarrhoeal diseases managed?

Answer 4

Fluid & electrolytes

Control

antibiotics – only for patients with high risk criteria

(Antimotility drugs - best avoided)

Question 5

What is

1. Infection
2. Intoxication

Answer 5

1. The illness is associated with proliferation of pathogenic microbes in infected host
2. The illness is associated with the presence of a preformed toxin in the food

Note: Some bacteria produce toxins during infection – Clostridium difficile (ie not preformed but produced in the gut)

Question 6

Which Bacteria cause INTOXICATION?

Outline the process.

Answer 6

• Bacillus Aureus
• Staphylococcus Aureus
• Clostridium Perfringens
• Clostridium Botulinum

Bacteria grows in food

Makes toxin

Ingested

=>V&D…. Or worse!

SHORT INCUBATION = 2-12hours

Question 7

Which bacteria cause INFECTION?

Answer 7

• Salmonella
• Shigella
• Escherichia coli
• Vibrio cholerae
• Campylobacter
• Clostridium difficile
• Listeria monocytogenes

Bacteria get in via mouth

(Hu-Hu faeco-oral /

Zoonotic / via food)

Multiples in gut

=> V&D…. Or worse!

LONGER INCUBATION = DAYS

Question 8

Which has the LONGER incubation period, infection or intoxication?

Answer 8

Infection (days)

Question 9

1. What family are salmonella from?
2. Do they normally inhabit the human gut?
3. How many serotypes?
4. Give some examples of serotypes

Answer 9

1. Enterobacteriaceae (Gram –ve rods family )
2. No
3. >2000 serotypes based on O and H antigens
4. Salmonella Belfast

Salmonella Dublin

Salmonella typhi

Salmonella paratyphi

Salmonella typhimurium

Salmonella enteritidis

Question 10

What are the two main syndromes caused by salmonella?

What sized-innoculum is needed?

Answer 10

Enterocolitis

• a zoonosis
• about 2,000 named organisms
• Most important S. typhimurium & S. enteritidis

Enteric Fevers

• not a zoonosis - human to human transmission
• Salmonella typhi

Salmonella paratyphi

need a large innoculum- 1000s of bacteria

Question 11

Salmonella causing Enterocolitis

1. How is it transmitted?
2. What is the incubation period?
3. What are the symptoms of Enterocolitis?
4. How long will Enterocolitis last for?
5. How is it diagnosed?
6. How can it be managed?

Answer 11

1. To humans via contaminated food and person to person
2. 6hours-2days
3. nausea, vomiting, abd. cramps, and non-bloody diarrhoea
4. 2-7days
5. Culture on selective media or PCR
6. Fluid & electrolyte replacement may be needed
   
   1. Salmonella (non-typhoid)

Treat invasive or severe infection only (rare) or if immunocompromised Ciprofloxacin or cefotaxime

Question 12

Salmonella causing Enteric Fever

1. What bacteria causes this?
2. How is it transmitted?
3. What is the incubation period?
4. What are the symptoms?
5. How long does it last?
6. How is it diagnosed?
7. How can long term carriers be identified?
8. What is the treatment?

Answer 12

1. S. typhi and paratyphi
2. Human to human
3. 10 to 14 days
4. Fever with headaches, myalgias, malaise (can be severe sepsis)
5. 1 week followed by diarrhoea
6. Culture on selective media
7. Post infection carriers- long term in some – gall bladder colonisation
8. Ciprofloxacin or cefotaxime

Constipation and muscle cramps, seen in returning travellers

Question 13

Shigella

1. What family is shigella from?
2. How is transmitted?
3. How many species cause bacillary dysentry? Which is the most serious?
4. What are most cases caused by?

Answer 13

1. Gram –ve rods- enterobacteriacea
2. Strictly human pathogen -spread by fecal-oral route => V. infectious (small infective dose)
3. 4 Species. S. dysenteriae
4. S. sonnei

Question 14

1. What is Bacillary Dysentry?
2. Who does it affect?
3. What are the symptoms?
4. What is the treatment?

Answer 14

1. Shigellosis
2. Primarily a pediatric disease
3. Short IP- diarrhea is watery initially, but later contains mucus & blood & pus- abdominal cramps & fever
4. Antibiotics should only be given for severe shigella diarrhoea – susceptibility testing important
   
   1. BNF: Antibacterial not indicated for mild cases.

Ciprofloxacin or azithromycin

Alternatives if micro-organism sensitive, amoxicillin or trimethoprim

Question 15

Escherichia coli

1. ​What family is E.Coli from?
2. How many different groups of E.Coli are there?
   
   1. What is ETEC?
   2. What is EPEC?
   3. What is EHEC? (tests are carried out to distinguish groups)
   4. Is antibacterial therapy indicated?

Answer 15

1. Gram –ve rods - enterobacteraceae (some strains are normal gut flora others cause infections)
2. 6 with different pathogenetic mechanisms some invasive, others toxigenic
   
   1. enterotoxigenic E.coli (causes traveller’s diarrhoea)
   2. enteropathogenic E.coli (cause diarrhoea in babies)
   3. enterohaemorrhagic E.coli Haemolytic uraemic syndrome
   4. NO

Question 16

EHEC enterohaemorrhagic E.coli

1. What does it cause?
2. What is a complication?
3. Where is it from?
4. What is the gene that can be detected by PCR?
5. What is the most common serotype?

Answer 16

1. Causes bloody diarrhoea with abdominal cramps but no fever
2. Haemolytic uraemic syndrome
3. Zoonotic - from farm animals. Associated with eating undercooked, ground beef & raw milk or contact with animals. Outbreaks and sporadic cases are common.
4. Verotoxin gene
5. O157:H7

Question 17

1. What are the symptoms of haemolytic uremic syndrome?
2. How is it diagnosed?
3. What can be seen?
4. Why is treatment urgent?

Answer 17

1. anaemia, thrombocytopenia, renal failure
2. High concerns- routine screen

–O157 sorbitol-non fermenter-

–Detection of toxin production

–Molecular

3. Verotoxin-producing E. coli infection, showing fibrin ‘thrombi’ in glomerular capillaries in HUS
4. It is a public health concern

Question 18

Cholera

1. What is it caused by?
2. What are the symptoms?
3. What is critical in the treatment?

Answer 18

1. Acute infection - caused by the comma-shaped Gram-ve acterium V. cholerae serotype 01. Symptoms are due to enterotoxin
2. Toxin causes fluid loss & painless, profuse, watery diarrhea…death by dehydration and electrolyte imbalance if untreated
3. Fluid replacement

Question 19

Cholera - Epidemiology

1. Where is infection acquired from?
2. What biotype?
3. What is the newest strain?

Answer 19

1. Contaminated water supplies
2. The El Tor biotype has largely displaced the classical biotype
3. a new non-O1 strain (0139) (1992)

Question 20

1. What is the most common cause of food-associated diarrhoea in the uk?
2. What is the organism’s appearance?
3. Which species causes most human infection?
4. What is the main reservoir and how does it spread?
5. How is it diagnosed?
6. Where does campylobacter grow best?

Answer 20

1. Campylobacter
2. Curved or S-shaped Gram negative rods
3. C.Jejuni
4. Large animal reservoirs and spread via food chain
5. Special laboratory culture requirements
6. Microaerophilic – grows best where there is a CO2 rich environment

Question 21

Campylobacter enteritis

1. ​​How long does it last for?
2. What are the symptoms?
3. What is a rare complication?
4. What is the treatment for Campylobacter enteritis?

Answer 21

1. IP 3-10d duration of symptoms 1 week
2. Initial symptom fever > 40°C, Abdominal pain & blood in faeces are notable features
3. Guillain- Barre syndrome
4. Frequently self-limiting; treat if immunocompromised or if severe infection.

Clarithromycin

Alternative, ciprofloxacin

Strains with decreased sensitivity to ciprofloxacin isolated frequently

Question 22

1. What causes Antibiotic associated diarrhoea?
2. Why does Clostridium Difficule grow?
3. How can spread occur?
4. What is it a common cause of?
5. What is it’s mechanism of action?
6. What can result?
7. What new strain has occurred?
8. How is it diagnosed?
9. What is the treatment?

Answer 22

1. Cl. Difficile
2. Component of normal gut flora ; flourishes under selective pressure of antibiotics (broad-spectrum) Importance: Antibiotic Stewardship / Outbreak Ward Rounds
3. Person to person.

• Spores are infectious
• Resistant to alcohol products

4. Hospital acquired infectious diarrhoea
5. Produce both an enterotoxin (A) and cytotoxin (B)
6. Pseudo-membraneous colitis- can be rapidly fatal
7. Cl. difficile 027
8. Detection of toxin in faeces
9. Metronidazole or vancomycin

Question 23

Clostridium difficile infection - BNF

• What does the BNF recommend as first line treatment?
• What does it suggest for subsequent infection/severe infection/infection not not responding to metronidazole?
• What does it suggest for infection not responding to vancomycin/life-threatening infection/patients with ileus?

Answer 23

• Oral metronidazole

–Suggested duration of treatment 10–14 days

• For third or subsequent episode of infection, for severe infection, for infection not responding to metronidazole, or in patients intolerant of metronidazole, oral vancomycin

–Suggested duration of treatment 10–14 days

• For infection not responding to vancomycin, or for life-threatening infection, or in patients with ileus, oral vancomycin + i/v metronidazole

–Suggested duration of treatment 10–14 days

Question 24

What can PCR Ribotyping be used for?

Answer 24

If the same type of C.diff is present = outbreak

If different types = random infections

Every C.Diff positive patient is ribotyped

Question 25

**Viral Diarrhoea** 1. Viral causes make up what percentage of diarrhoea? 2. Why is it a cause for concern? 3. How is it transmitted? 4. What are the main symptoms? 5. What are the two important viruses to consider? 6. What is treatment?

Answer 25

1. 30-50% 2. Appalling morbidity and mortality especially in young children in poor countries 3. Faeco-oral route 4. watery diarrhea and vomiting 5. Rotaviruses & Norovirus 6. Largely supportive - no specific treatment

Question 26

Name the virus associated with viral diarrhoea

Answer 26

* Rotaviruses * Noroviruses * Adenoviruses (group F) * Astroviruses

Question 27

What is the most common cause of viral gastroenteritis?

Answer 27

**Rotavirus** * Medium sized * Segmented dsRNA virus **Norovirus** * Small * ssRNA virus

Question 28

**Rotaviruses** 1. Describe their genome 2. Describe their mechanism 3. What kind of diarrhoea do they cause? 4. Who is the infection most common in? 5. How is it diagnosed? 6. How is it treated?

Answer 28

1. Wheel-shaped - 11 genome segments -dsRNA virus 2. •Replicating viruses cause diarrhea by damaging transport mechanisms in gut. No inflammation or loss of blood. 3. **Acute onset of vomiting and diarrhea** which lasts 4 days (dehydration common) 4. ***_Children under 2 years of age_*** (outbreaks often seen in nurseries). Seasonal pattern (cooler months) - Small infective dose. 5. Viral particles can be seen by electron microscopy. **Detection of viral RNA / antigen** 6. Fluid and salt replacement •**UK Vaccine** introduced from 2013

Question 29

**Noroviruses** 1. What types? 2. Where are the outbreaks? 3. When is it more likely? 4. **Who is it more common in**? 5. What symptoms does it give rise to? 6. How is it Diagnosed? 7. Is there a vaccine?

Answer 29

1. Calicivirus- SS RNA virus - SRSV or NLV 2. in closed groups – nursing homes / hospitals 3. Winter = 'the winter vomiting disease' 4. ***_Older children and adults_*** 5. •Acute gastroenteritis, sporadic & outbreaks •Usually presents as acute-onset vomiting, watery non-bloody diarrhea 6. Realtime PCR 7. No

Question 30

Summarize 1. **Rotaviruses** 2. **Noroviruses**

Answer 30

**1. Rotaviruses** * Mainly diarrhoea * \<2 years of age * Severe presentation –dehydration common, major killer in 3rd world * Incubation 1-2 days * Duration ~ 4 days **2. Noroviruses** * Mostly vomiting, (‘Winter vomiting disease’) * All ages * Outbreaks in community, institutions, hospitals & Food associated outbreaks * Incubation 1-2 days * Duration 2 days

Question 31

How is Viral Gastroenteritis diagnosed?

Answer 31

* **PCR** * Sensitive especially useful for Norovirus where other techniques are insensitive * **Electron microscopy** * **Antigen detection** (eg ELISA) * Especially useful for Rotavirus

Question 32

What is the treatment for Viral Gastroenteritis?

Answer 32

* **No specific treatment** * Supportive only * Oral / IV dehydration * **Vaccine for Rotavirus introduced 2013** * Live * Oral * Started at 2 months of age

Question 33

What is the approach for testing faecal samples for enteric pathogens?

Answer 33

* Routine on all specimens (**PCR**): * Salmonella spp * Shigella spp * Campylobacter spp * Ecoli O157: H7 (verotoxin) * Cryptosporidium spp * On request + specific wards: **Clostridium difficile (PCR and toxin)** * Suspected food poisoning : need to look at **FOOD**! * Cl. perfringens * Staph aureus * Bacillus cereus * **History of foreign travel** → Vibrio cholera (culture) * **PCR** for gastroenteritis viruses: Astro, Rota, Adeno, Noro (on request + outbreaks)

Question 34

What is the general approach to gasto-enteritis?

Answer 34

Antibacterial drugs are generally unnecessary in simple gastro-enteritis because the complaint usually resolves quickly without them, and infective diarrhoeas in the UK often have a viral cause * Self-limiting