Infectious diarrhoea

Question 1

What is Gastroenteritis?

Answer 1

inflammation of the stomach and intestines, typically resulting from bacterial toxins or viral infection and causing vomiting and diarrhoea.

Question 2

How is diarrhoea defined?

Answer 2

 3 or more loose or watery stools per day

 faeces that fits the receptacle it is in

Question 3

What are the pathological mechanism of diarrhoea?

Answer 3

• toxin mediated
• damage to intestinal epithelial surface
• invasion across intestinal epithelial barrier

Question 4

How can toxins be produced?

Answer 4

o Produced prior to consumption (S.aureus, B.cereus)

• Toxins are liberated onto food by the bacteria before the food is consumed
• Hallmark = sickness a few hours after eating

o Produced after consumption (C.difficile, E.coli 0157)
- Once consumed, the organism replicates within the gut and produces toxins

Question 5

How can epithelial damage cause diarrhoea?

Answer 5

o Direct toxic effect to cells

o Inflammation of the gut causes diarrhoea = gut tries to evacuate the pathogen

Question 6

What are the three main symptoms to look for in a patient presenting with diarhoea

Answer 6

• vomiting
• type of diarrhoea
• non-intestinal manifestations

Question 7

What is the significance of vomiting in a patient with diarrhoea

Answer 7

(nausea common, vomiting uncommon)

o Sudden onset within 6-12hrs of food ingestion suggests pre-formed toxin (in food)
 S. aureus
 B. cereus - e.g. in contaminated rice

o Viral aetiology
 Norovirus
 Sapovirus

Question 8

How can diarrhoea be classed?

Answer 8

classified according to where the predominant infection is:

• small intestine
• large intestine

Question 9

What are the symptoms associated with small intestine diarrhoea?

Answer 9

(digestion and absorption) infection will result in:
o high volume diarrhoea
o a lot of cramping (stretching of small intestine)
o weight loss when chronic (due to impaired nutrient absorption)
o bloating
o wind

Question 10

What are the symptoms of large intestine diarrhoea?

Answer 10

= (fluid and electrolyte absorption) colitis:
o frequent diarrhoea
o small amounts
o Often contains blood
o Fever
o Painful stool

Question 11

What are the most common bacterial causes of diarrhoea?

Answer 11

 Campylobacter sp – by far the most common bacterial cause of gastroenteritis
 Salmonella sp – battery hens are vaccinated against salmonella, greatly reducing prevalence
 Shigella sp – often seen in travellers
 E. coli (0157: H7)
 Clostridium difficile

Question 12

What are the most common viral causes of diarrhoea?

Answer 12

 Norovirus
 Sapovirus
 Rotavirus – common cause of D&V in children
 Adenoviruses – red eye, vomiting, diarrhoea

Question 13

What are the most common parasitic causes of diarrhoea?

Answer 13

 Cryptosporidium – causes small bowel infection
o Colonises the gut of lambs – common in lambing season (infects water supply from faeces
washout)
 Giardia – travel related
 Entamoeba histolytica – LI infection, travel related
 Cyclospora - travel related (often seen in Mexico)
 Isospora - travel related

Question 14

What should be enquired during a history of a patient with diarrhoea?

Answer 14

• Food history
• Onset & nature of symptoms
• Residence
• Occupation
• Travel
• Pets / hobbies
• Recent hospitalisation / antibiotics
• Co-morbidity

Question 15

What is the use of Faecal leukocytes & occult blood testing?

Answer 15

Both a waste of time, not used clinically at all in the UK

(idea is that presence of faecal leukocytes may indicate a colonic or “inflammatory” cause
o Poor sensitivity & specificity
o Not used clinically

Faecal occult blood
o Bacterial cause
Faecal calprotectin
o Protein found in stool that can be elevated with inflammation in the gut
o Can be raised but NOT specific for infection

Question 16

What is the use of obtaining a stool culture?

Answer 16

Necessity of documenting a pathogen
o Self-limiting illness
o Indications for treatment – whether or not to give antibiotics
o Public health implications – limiting spread of infection (e.g. preventing people from handling
food while infected)

Consider microscopy for ova and cysts if parasitic cause is possible
o Travellers
o Epidemiology

Question 17

What are the disadvantages of stool cultures?

Answer 17

Low rate positive stool cultures (1.5-5.6% of patients)
o Viral causes cannot be cultured
o Organisms in the gut are used to very specific environmental conditions, and this is incredibly
difficult to reproduce in the lab
o Campylobacter is very difficult to culture
o Many patients will therefore have a false negative

Question 18

What is the use of endoscopy in patients with diarrhoea?

Answer 18

 Not very useful, as it does not add to diagnosis with infective diarrhoea
 Can indicate colitis, but not the source of infection
 Useful when patient has diarrhoea but no infection  can be used to rule out disorders of the gut, e.g.
UC/Crohn’s with biopsies

Question 19

How is infectious diarrhoea treated?

Answer 19

 Oral rehydration solution – morbidity can result from dehydration
o Small intestinal Na-glucose cotransport remains intact
o Can absorb water if Na & glucose also present (osmotic potential)

 May require IV fluid replacement
o Vomiting

Question 20

Should antibiotics be given to patients with diarrhoea?

Answer 20

 Self-limiting illness – antibiotics are usually not required
 Antibiotics reduce duration of diarrhoea by about 1 day (1.7 v 2.8 days)
o This is not worth the damage antibiotics do to the patient or the risk of antibiotic resistance
 Antibiotics can WORSEN outcome in some illnesses
o E. coli 0157:H7

Question 21

Which patients should receive antibiotics?

Answer 21

• v. ill
• septic/ evident bacteraemia
• significant co-morbidity
• certain causes

Question 22

What cause of diarrhoea should be given antibiotics and what antibiotic should be given?

Answer 22

C. difficile associated diarrhoea (metronidazole)

Question 23

What is the use of treating symtpoms of diarrhoea?

Answer 23

e.g. Imodium
 Generally not indicated
 Potentially worsens prognosis in bacterial disease but may be safe given with antibiotics for travellers
 Diarrhoea is the body’s way of eliminating the organism
 Slowing this down may prolong the duration of illness

Question 24

In what situations can exclusion diets be helpful?

Answer 24

o Could potentially be beneficial in managing C.difficile infection
o Travellers diarrhoea = cutting out lactose helps with giardia infection

Question 25

What is the common cause of Campylobacter diarrhoea?

Answer 25

Most common source is chicken

Question 26

What is the pathophysiology of campylobacter diarrhoea?

Answer 26

```  Infecting dose of ~9000 organisms  Sensitive to stomach acidity o Beware things that reduce stomach acidity, e.g. PPIs = increase susceptibility to infection  Attach and invade intestinal epithelial cells o Small bowel o Large bowel o Causes mixed diarrhoea  Incubation period 3 days (1 to 7 days) o Depends on infecting dose ```

Question 27

What are the clinical features of campylobacter diarrhoea?

Answer 27

```  Diarrhoea o Frequent and can be high volume o Blood in stool common  Abdominal pain (cramping)  Often severe  Nausea common / vomiting rare  Fever ```

Question 28

How is campylobacter diarrhoea managed?

Answer 28

 Clinical course o Self-limiting (7 days)  Antibiotics usually not given, rarely indicated o High rates of antibiotic resistance o Can develop resistance to the antibiotic used on treatment

Question 29

What are late complications of campylobacter diarrhoea?

Answer 29

o Reactive arthritis | o Guillain-Barre

Question 30

What is the main source of SALMONELLA diarrhoea?

Answer 30

 Main source = chicken, reptiles (excrete salmonella on their skin)  Spreads person-to- person

Question 31

Describe the pathophysiology of salmonella diarrhoea

Answer 31

 Numerous serotypes, but generally split into: o Typhoidal (travellers) o Non-typhoidal  Infectious dose ~10,000 organisms  Interactions with host o Increased risk with decreased stomach acid (PPIs, H2RA, etc.) o Increased risk with diminished gut flora  Invasion of enterocytes with subsequent inflammatory response o Can cause bacteraemia/systemic infection

Question 32

What are the clinical features of salmonella diarrhoea

Answer 32

 Illness within 72 hours of ingestion  Onset of illness depends on inoculum; higher inoculum  more rapid onset  Nausea, diarrhoea, abdominal cramps, fever  Invasive disease o Bacteraemia in <5% o Secondary infection (endocarditis, osteomyelitis, mycotic aneurysm)

Question 33

How should salmonella diarrhoea be treated?

Answer 33

```  NB: when patients with gastroenteritis are treated with antibiotics its normally because of the fear of invasive salmonella  Antibiotics o Self-limiting (up to 10 days) o No significant reduction in duration o Severe disease ```

Question 34

What are the public health implications of salmonella diarrhoea?

Answer 34

Clear implications for food handlers (due to person-person transmission) o Asymptomatic shedding common & episodic o Median 5 weeks o Negative stool cultures (>1)

Question 35

What is the main source of e.coli 0157

Answer 35

 Found in beef mince, but also in vegetables (bean sprouts, spinach) because of fertiliser (animal faeces)  Person-person transmission  Commonly caught at petting zoos  Excreted by animals with more than one stomach

Question 36

What is the pathogenesis of e.coli 0157

Answer 36

```  Attachment to large bowel  Shiga toxin production o Enterocyte death o Enters systemic circulation  Infectious load as little as 10 organisms – incredibly infectious  Sporadic outbreaks ```

Question 37

What are the clinical features of e coli 0157

Answer 37

 Incubation period 3 to 4 days  Bloody diarrhoea & abdominal tenderness  Fever is rare > Haemolytic Uraemic Syndrome

Question 38

What is Haemolytic Uraemic Syndrome?

Answer 38

Systemic effect of shiga toxin Triad of: o Microangiopathic haemolytic anaemia (formation of fibrin clots in small blood vessels => RBC sheared open when they pass) o Acute renal failure (most small blood vessels in the kidney) o Thrombocytopenia (because platelets used in the clots)

Question 39

What is the incidence of Haemolytic Uraemic Syndrome?

Answer 39

Only occurs in up to 9% patients Tends to come on 5 to 10 days after onset diarrhoea o Diarrhoea may already have cleared

Question 40

How is Haemolytic Uraemic Syndrome treated?

Answer 40

```  50% require dialysis o Mortality 3 to 5% o Association with antibiotics  Poorer outcome with antibiotics  Management o Supportive, elimination of toxin (dialysis etc.) ``` ```  Prevention is key o Strict infection control for healthcare workers o Screening of contacts o Appropriate butchering of meat o Public health measures in outbreaks ```

Question 41

What are the risk factors for clostridium difficile infection?

Answer 41

- antibiotic exposure - older age (>65 - ?PPI use) - hospitalisation Elderly are at higher risk because gut microbiota decreases with age

Question 42

Describe the pathogenesis of clostridium difficile infection?

Answer 42

Destruction of gut microbiota allows colonisation by other bacteria => toxin production

Question 43

What are the symptoms of clostridium difficile infection?

Answer 43

 Loose stool & colic  Fever  Leukocytosis – because it is toxin-mediated  Protein losing enteropathy – any condition of the GI tract that results in a net loss of protein from the body (e.g. damage to the gut wall)  Pseudomembranous colitis – masses of puss on surface of colon

Question 44

How is C diff detected?

Answer 44

Toxin detection via: - tissue culture assay (no longer commonly used) - c. diff antigen/ c. diff toxin first test for antigen, then test for toxin

Question 45

How is c. diff treated?

Answer 45

 Stop causative antibiotics if possible (or at least narrow spectrum) o Allows normal gut flora to grow back  Metronidazole / Vancomycin  Faecal transplant - recolonise with normal flora o 96% cure rate

Question 46

Describe norovirus

Answer 46

Norovirus most common cause of epidemics o Tends to cause outbreaks within institutions (hospitals, care homes, nurseries, etc.) o Can lead to hospital ward closure Occur in all months with peak in winter

Question 47

How is norovirus transmitted?

Answer 47

o Faecal oral route o Infectious dose 10 – 100 viruses o Very stable organism (can survive up to 60°C, bleach, and utterly resistant to alcohol gel)  Must wash hands with soap and water, physically wash the virus off

Question 48

What are the clinical features of norovirus?

Answer 48

o Acute explosive diarrhoea and vomiting o Causes illness within 24 – 48 hours o No lasting immunity