Lecture 1: Infectious Diarrhoea

Question 1

what is dysentry?

Answer 1

large bowel inflammation, bloody stools

Question 2

what ways can a person get gastro-enteritis?

Answer 2

• contamination of foodstuffs: intensively farmed chicken and campylobacter
• poor storage of produce: bacterial proliferation at room temp.
• travel-related infections e.g. salmonella
• person to person spread e.g. norovirus

Question 3

what pathogens are the most common cause of gastroenteritis?

Answer 3

• viruses are most common cause
• campylobacter is the most common bacterial pathogen

Question 4

what is the most common pathogen causing hospital admissions with food poisoning?

Answer 4

salmonella

Question 5

list the defences against enteric infections

Answer 5

• hygiene
• stomach acidity: antacids and infection
• normal gut flora: C.diff diarrhoea
• immunity: HIV + salmonella

Question 6

what are the different types of diarrhoea?

Answer 6

• non-inflammatory/secretory
• inflammatory
• mixed picture

Question 7

features of non-inflammatory/secretory diarrhoea

what causes it, how does it present, whats the treatment

Answer 7

• toxin-mediated usually e.g. cholera and E.coli
• watery stools, rapid dehydration, relatively little abdo pain
• rehydration mainstay of treatment

Question 8

features of inflammatory diarrhoea

what causes it, how does it present, whats the treatment

Answer 8

• bacterial infection usually e.g. shigella dysentery
• abdo pain, bloody stools, systemic upset
• rehydration and (sometimes) antimicrobials required

Question 9

what organism typically causes diarrhoea with a mixed-picture i.e. non-inflammatory (secretory) and -inflammatory?

Answer 9

C.difficile

Question 10

which organsims commonly cause non-inflammatory diarrhoea?

Answer 10

• cholera
• E.coli

Question 11

how does cholera cause diarrhoea?

Answer 11

• increased cAMP results in loss of Cl- from cells along with Na and K.
• osmotic effect leads to massive loss of water from the gut.

Question 12

how would we assess a patient with diarrhoeal illness?

Answer 12

• inquire about their symptoms and duration
• assess risk of food posioning: dietary, contact, travel history
• assess hydration: postural BP, skin turgor, pulse
• are there features on inflammation? fever, raised WCC

Question 13

describe the fluid and electrolyte losses due to diarrhoeal illness

Answer 13

• can be severe with secretory diarrhoea: 1-7L fluid per day containing 80-100 mmol Na
• hyponatraemia due to sodium loss with fluid replacement by hypotonic solutions
• hypokalaemia due to K loss in stool (40-80mmol/l of K in stools)

Question 14

diarrhoeal illness investigations

Answer 14

• stool culture +/- molecular or Ag testing
• blood culture
• renal function
• blood count: neutrophilia, haemolysis (E.coli O157)
• abdo x-ray/CT if abdomen distended, tender

Question 15

features of campylobacter gastroenteritis

Answer 15

• C.jejuni principle pathogen
• incubation up to 7 days
• infection clears within 3 weeks
• severe abdo pain =/- colitic picture
• rarely invasive < 1%
• post-infective sequelae: Guillaine-Barre syndrome, reactive arthritis

Question 16

which two species of campylobacter cause the most infections?

Answer 16

C.jejuni (90%)
C.coli (9%)

Question 17

sources of Campylobacter infection

Answer 17

• chickens
• contaminated milk
• puppies

Question 18

del

Question 19

Features of E.coli O157:H7

Answer 19

• enterohaemorrhagic E.coli
• cattle reservoir
• excretion over three weeks after symptoms
• produce a shiga-like toxin (SLT)
• 5-9 days between onset of diarrhoea and haemolytic uremic syndrome (HUS)
• HUS largely a complication in children and elderly

Question 20

features of Shigella infection

Answer 20

• largely a disease of childhood/travel
• HUS and seizures may complicate
• widespread quinolone against shigellosis in developing world leading to resistance
• different serotypes hamper development of a universal vaccine

Question 21

features of Traveller’s diarrhoea

Answer 21

• enterotoxigenic E.coli, campylobacter and shigella account for 80% of tourist infections (Nepal)
• about 1/3 travellers develop a bout of diarrhoea
• usually lasts < 1 week but persistent diarrhoea (> 30 days) in 1-3%
• significant shortening by antibiotics

Question 22

features of viral gastro-enteritis

Answer 22

• rotavirus is most common viral enteropath
• > 800,000 deaths in children under 5y
• faecal-oral transmission
• infects mature enterocytes of villous body and tip with cell death and lactose intolerance.

Question 23

list some intestinal parasites

Answer 23

• Cryptosporidiosis
• Giardia
• entamoeba histolytica

Question 24

gastroenteritis diagnostic requirements

Answer 24

• 3+ stools in 24 hours plus at least one of fever, vomiting, pain, blood/mucus stools

Question 25

features of Cryptosporidiosis

Answer 25

- water-borne outbreaks - 3-6% diarrhoea in developed countries - cattle the principle reservoir - oocysts seen on microscopy - self-limiting, but often protracted illness, in non-compromised patients

Question 26

features of Giardia

Answer 26

- present in surface water - asymptomatic cyst carriers - treatment by metronidazole, tinidazole

Question 27

features of Entamoeba histolytica

Answer 27

- microscopy only 50% sensitive - may mimic ulcerative colitis - treat symptomatic disease with 10/7 metronidazole and furamide for cyst carriage

Question 28

what % of patients given antimicrobials get diarrhoea?

Answer 28

5-10%

Question 29

C.difficile is present in what percentage of antibiotic associated diarrhoea (AAD)? AND WHY?

Answer 29

10-15% overgrowth of C.diff and production of toxins A > enterotoxin and B > cytotoxin

Question 30

antibiotic associated diarrhoea (AAD) treatment

Answer 30

- metronidazole (up to 6% resistant, poor stool concn.) - vancomycin (cost and drug resistance in gut flora) - teicoplanin/fusidic acid/cholestyramine - surgery

Question 31

commonest salmonella isolates in the UK

Answer 31

- salmonella enteriditis - salmonella typhimurium

Question 32

HUS is characterised by

Answer 32

- renal failure - haemolytic anaemia - thrombocytopenia

Question 33

list some occasional causes of food poisoning outbreaks

Answer 33

- Staph aureus (toxin) - Bacillus cereus (re-fried rice) - Clostridium perfringens (undercooked meat/cooked food left out - toxin accumulates in spore formation)

Question 34

when are antibiotics indicated for gastroenteritis

Answer 34

- immunocompromised - severe sepsis or invasive infection - chronic illness e.g. malignancy - not indicated for healthy hapteint with non-invasive infection

Question 35

treatment for C.diff diarrhoea

Answer 35

- metronidazole (if no severity markers) - oral vancomycin (if 2 or more severity markers) - fidaxomicin (new and expensive) - stool transplants - surgery may be required

Question 36

how can C.diff infection be prevented?

Answer 36

- reduction in broad spectrum antibiotics prescribing - avoid 4Cs- cephalosporins, co-amoxiclave, clindamycin, ciprofloxacin - antimicrobial management team and local antibiotic policy - isolate symptomatic patients - wash hands between patients - contaxt precautions - cleaning environment

Question 37

how is norovirus diagnosed?

Answer 37

PCR

Question 38

list the bacterial species that are routinely sought in stool specimens

Answer 38

- campylobacter - salmonella - shigella - e.coli O157 - cholera (under specific circumstances)