MB9 Gastrointestinal Infections 1 Flashcards Preview

Pathology > MB9 Gastrointestinal Infections 1 > Flashcards

Flashcards in MB9 Gastrointestinal Infections 1 Deck (34):

What are the body's natural barriers to infection?


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

  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


How are these different causes of diarrhoea diagnosed?

  1. Bacteria
  2. Viruses
  3. Parasites

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

(all from faeces)


In general, how are diarrhoeal diseases managed?

Fluid & electrolytes


antibiotics – only for patients with high risk criteria

(Antimotility drugs - best avoided)


What is 

  1. Infection
  2. Intoxication

  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)


Which Bacteria cause INTOXICATION?

Outline the process.

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

Bacteria grows in food

Makes toxin


=>V&D.... Or worse!




Which bacteria cause INFECTION?



•Escherichia coli

•Vibrio cholerae


•Clostridium difficile

•Listeria monocytogenes


Bacteria get in via mouth

(Hu-Hu faeco-oral /

Zoonotic / via food)

Multiples in gut

=> V&D.... Or worse!




Which has the LONGER incubation period, infection or intoxication?

Infection (days)


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

  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


What are the two main syndromes caused by salmonella?





What sized-innoculum is needed?


  • 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


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?

  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


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?

  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



  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?

  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   


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

  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


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?

  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


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?

  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 


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

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

    –O157 sorbitol-non fermenter-

    –Detection of toxin production


  3. Verotoxin-producing E. coli infection, showing fibrin 'thrombi' in glomerular capillaries in HUS

  4. It is a public health concern



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

  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


Cholera - Epidemiology 

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

  1. Contaminated water supplies
  2. The El Tor biotype has largely displaced the classical biotype 

  3. a new non-O1 strain (0139) (1992)


  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?

  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 


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?

  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.


    Alternative, ciprofloxacin

    Strains with decreased sensitivity to ciprofloxacin isolated frequently


  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?

  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


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?

  • 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


What can PCR Ribotyping be used for?

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

If different types = random infections

Every C.Diff positive patient is ribotyped


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?

  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


Name the virus associated with viral diarrhoea



•Adenoviruses (group F)



What is the most common cause of viral gastroenteritis?


•Medium sized

•Segmented dsRNA virus



•ssRNA virus



  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?

  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


    Fluid and salt replacement 


    UK Vaccine introduced from 2013  




  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?

  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



  1. Rotaviruses
  2. Noroviruses

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


How is Viral Gastroenteritis diagnosed?

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


What is the treatment for Viral Gastroenteritis?

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


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

  • 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)


What is the general approach to gasto-enteritis?

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