Infectious Diarrhoea

Question 1

List the bacteria that are sought by ROUTINE culture of stools from patients with diarrhoea in the UK and outline their epidemiology

Answer 1

Bacteria

• Campylobacter - most common bacterial cause - chicken, milk, puppies
• Salmonella - causes most admissions - often travel related
• E. Coli O157 - contaminated meat or person-person
• Shigella - nurseries

Question 2

List other NON-ROUTINE bacteria that cause diarrhoea, indicate the availability of routine tests for them & outline their epidemiology

Answer 2

SA - toxin
Bacillus cereus - refried rice
Clostridium perfringens - toxin
C. Diff - toxin-detected
Enteropathogenic, enterotoxic, enteroinvasive E. coli not routinely detected 
Vibrio cholerae

Question 3

List the parasites commonly detected in stool specimens in the UK by microscopy and
outline their epidemiology

Answer 3

Common

• Cryptosporidiosis - waterborne, cattle reservoir
• Giardia - surface water,

Entamoeba histolytica - uncommon

Question 4

List the viruses that commonly cause diarrhoea and outline their epidemiology and
how they are detected.

Answer 4

Rotavirus - most common, faecal-oral
Norovirus - common cause of outbreaks, hospitals/cruise ships

PCR (antigen detection)

Question 5

Define gastro-enteritis and dysentery

Answer 5

Gastro-enteritis
- 3+ stools in 24hrs plus at least one of fever, vomiting, pain, blood/mucus stools

Dysentery
- large bowel inflammation, bloody stools

Question 6

General sources of viral/bacterial gastroenteritis

Answer 6

Food contamination - e.g. chicken and campylobacter
Poor storage of produce
Travel-related e.g. Salmonella
Person to person e.g. Norovirus

Question 7

Host factors affecting spread of enteric infection.

Answer 7

Age
Hygiene
Stomach Acidity/Gastric Motility
Normal flora
Immunity

Question 8

What are the mechanisms by which infecting organisms can produce diarrhoea? What are some examples?

Answer 8

Toxin

• e.g. Cholera (inc cAMP and Cl secretion
• enterotoxigenic E. Coli (traveller’s diarrhoea)

Invasion

Others

Question 9

What to look out for in history AND the examination of someone with possible gastro-enteritis? How to differentiate inflammatory from non-inflammatory?

Answer 9

Non-Inflammatory
- Watery stools, rapid dehydration, relatively little abdo pain

Inflammatory

• Abdo pain, bloody stools, sytemic upset (fever)
• usually bacterial

If >2 weeks, unlikely to be infective gastro-enteritis
Take food history, travel history
Assess hydration - postural BP, turgor, pulse
Features of SIRS - fever, raised WCC

Question 10

What investigations should/could be performed?

Answer 10

Stool culture
Blood culture
Renal function
Blood count - neutrophilia, haemolysis
Abdominal X-ray if distension, tenderness
Sigmoidoscopy
Serology

Question 11

How are secretory diarrhoea and gastro-enteritis managed? Who should get more thorough treatment?

Answer 11

Non-inflammatory
- Rehydration mainstay of treatment

Gastro-enteritis

• Rehydration
• Antibiotics for: immunocompromised, severe sepsis/invasive infection, valvular heart disease, chronic illness, diabetes
• C. Diff with metronidazole/oral vancomycin/fidaxomicin
• Giardia and entamoeba with metronidazole

Question 12

Describe a potential complication of E. coli O157 (and the presentation) and treatments

Answer 12

Haemolytic-uraemic syndrome

Characterised by

• renal failure
• haemolytic anaemia
• thrombocytopenia

Antibiotics NOT indicated
- supportive treatment: fluid and electrolyte balance