Diarrhoea

Question 1

What are the three main bacteria that are sought by routine cultures of stools?

Answer 1

• Campylobacter
• E. coli O157
• Salmonella

Question 2

describe the incubation prossess Campylobacter?

Answer 2

○ Up to 7 days incubation so dietary history may be unreliable
○ Stools negative within 6 weeks
○ abdominal pain can be severe
○ <1% invasive

Question 3

What is the post infective sequelae of campylobacter?

Answer 3

Guillain-Barre syndrome, Reactive arthritis

Question 4

What is the routine bacterial culture of Campylobacter?

Answer 4

• specialised culture conditions

- C. jejuni/ C. coli

Question 5

Describe the natural history of Salmonella

Answer 5

○ symptom onset usually <48 hrs after exposure
○ diarrhoea usually lasts <10 days
○ <5% positive blood cultures
○ 20% patients still have positive stools at 20/52
○ Prolonged carriage may be associated with gallstones
○ Post-infectious irritable bowel is common

Question 6

What is the routine bacterial culture of Salmonella?

Answer 6

• screened out as lactose non-fermenters - then antigen and biochemical tests
• thousands (!) of species with individual names
• genetically most are serotypes of the same species (Salmonella enterica)
• traditionally named after place of first isolation
• Commonest isolates are Salmonella enteritidis and Salmonella typhimurium
• > 50% of these were imported from abroad in 2010
• N.B. - S. typhi and S. paratyphi cause enteric fever (typhoid and paratyphoid) and not gastro-enteritis

Question 7

How does E. coli O157 spread and how is the illness typically characterised?

Answer 7

○ Infection from e.g. contaminated meat or person-to-person spread (low inoculum)
○ Typical illness characterised by frequent bloody stools

Question 8

What are the other bacteria that cause diarrhea?

Answer 8

• Shigella (4 species) – outbreaks of Shigella sonnei in nurseries
• several other forms of E. coli cause diarrhoea
• enteropathogenic
• enterotoxic (traveller’s diarrhoea)
• enteroinvasive
• Occasional causes of food poisoning outbreaks
○ Staph aureus (toxin)
○ Bacillus cereus (re-fried rice)
○ Clostridium perfringens (toxin)

Question 9

How would you diagnose E. Coli (other than O157)?

Answer 9

• Routine diagnosis of these E. coli strains not possible – only O157 is easily distinguished from “ordinary” E. coli

Question 10

List the parasites commonly detected in stool specimens in the UK

Answer 10

• Protozoa and helminths
• Giardia lamblia
• Cryptosporidium parvum
• Entamoeba histolytica - amoebic dysentery

Question 11

What is the epidemiology of Cryptosporidium parvum?

Answer 11

○ first recognised in AIDS
○ contaminated water (animal faeces)
○ cysts seen on microscopy
○ no specific treatment usually required
○ 442 cases in Scotland in 2011

Question 12

What is Entamoeba histolytica?

Answer 12

○ vegetative form in symptomatic patient - (“hot stool”)
○ cysts seen in asymptomatic patient
○ amoebic liver abscess may be long term complication (“anchovy pus”)
○ treat with metronidazole

Question 13

What are the common viral causes of Diarrhea in the UK?

Answer 13

• Retrovirus
• Norovirus
• Adenovirus

Question 14

What is the epidemiology of Retrovirus?

Answer 14

• rotavirus in children under 5 years
• common in winter
• diagnosis by antigen detection
• 1465 laboratory reports in Scotland in 2011
• Routine vaccination 2013

Question 15

What is the epidemiology of norovirus?

Answer 15

○ Winter vomiting disease
		○ common cause of outbreaks
			§ hospital, community, cruise ships
		○ In Scotland in 2011:
			§ 1668 laboratory reports
			§ 175 recorded outbreaks
		○ diagnosis by PCR
		○ very infectious
		○ ward closures common – staff and patients affected
		○ strict infection control measures needed

Question 16

Define diarrhea, Gastroenteritis and dysentry

Answer 16

• Diarrhoea - subjective
○ fluidity and frequency
• Gastro-enteritis - objective
○ three or more loose stools/day
○ accompanying features
• Dysentery – obvious
○ large bowel inflammation, bloody stools

Question 17

How is bacterial and viral gastroenteritis spread?

Answer 17

• Contamination of foodstuffs
○ e.g. chicken and campylobacter
• Poor storage of produce
○ E.g. Bacterial proliferation at room temperature
• Travel-related infections e.g. Salmonella
• Person-to-person spread
○ e.g. norovirus

Question 18

What are the trends with bacterial and viral gastroenteritis?

Answer 18

• 25% of population have Infectious intestinal disorder each year
• 2% of population visit GP because of GI infection each year
• For each reported case there are 10 GP consults and 147 community cases that are unreported
• Viruses are commonest cause with campylobacter being the commonest bacterial pathogen

Question 19

What are the food poisoning trend?

Answer 19

○ There are more than 500,000 cases of food poisoning a year from known pathogens
○ Campylobacter is the most common foodborne pathogen, with about 280,000 cases every year
○ Salmonella is the pathogen that causes the most hospital admissions – about 2,500 each year
○ Poultry meat was the food linked to the most cases of food poisoning, with an estimated 244,000 cases every year

Question 20

How should someone assess a patient with gastroenteritis?

Answer 20

○ Symptoms and their duration 
- >2/52 unlikely to be infective gastroenteritis
○ Risk of food poisoning 
- Dietary, contact, travel history 
○ assess hydration
- postural BP, skin turgor, pulse
○ features of inflammation (SIRS)
- fever, raised WCC

Question 21

Describe the fluid and electrolyte loss in a patient with gastroenteritis?

Answer 21

○ Can be severe with secretory diarrhoea

• 1-7 l fluid per day containing 80-100 mmol Na
• Hyponatraemia due to sodium loss with fluid replacement by hypotonic solutions
• Hypokalemia due to K loss in stool (40-80 mmol/l of K in stools)

Question 22

What investigations should be carried out on a patient with gastroenteritis?

Answer 22

○ stool culture
○ blood culture
○ Renal function
○ blood count - neutrophilia, haemolysis
○ abdominal X-Ray if abdomen distended, tender

Question 23

What are the indications to give antibiotics to a patient with gastroenteritis?

Answer 23

• immunocompromised
• severe sepsis or invasive infection
• valvular heart disease
• chronic illness
• diabetes

Question 24

What are the complications of E. coli O157?

Answer 24

• Complications are caused by the toxin (not the bug) getting into your blood
• E. coli O157 produces verocytotoxin
• E. coli O157 stays in the gut but the toxin gets into the blood
• toxin can cause hemolytic-uraemic (HUS) syndrome (haemolytic anaemia and renal failure)
○ HUS characterised by renal failure, haemolytic anaemia and thrombocytopenia
○ Toxin binds to globotriaosylceramide
○ Platelet activation stimulated
○ micro-angiopathy results
○ attach to endothelial, glomerular, tubule and mesangial cells

Question 25

What is the treatment for the complications of E. coli O157?

Answer 25

Treatment supportive – antibiotics NOT indicated

Question 26

What is the commonest cause of bacterial food poisoning in UK?

Answer 26

Campylobacter

Question 27

Through what sources can Campylobacter be transmited?

Answer 27

chickens, contaminated milk, puppies

Question 28

Which is more common in Campylobacter: isolated cases or outbreaks?

Answer 28

Isolated cases

Question 29

What are the host’s natural defences against enteric

Infections?

Answer 29

• hygiene
• stomach acidity
○ antacids and infection
• normal flora
		○ Cl. difficile diarrhoea
		○ Protect against all forms of bacterioentrities 
• immunity
		○ HIV- salmonella

Question 30

Describe the mechanisms by which infecting organisms can produce diarrhoea

Answer 30

• Secretory toxin-mediated
○ cholera - increases cAMP levels and Cl secretion
○ enterotoxigenic E. coli (travellers’ diarrhoea)

Question 31

What are the treatments for gastroenteritis?

Answer 31

○ Rehydration - iv or oral?

		- Oral rehydration with salt/sugar solution
		- iv saline