Micro 12 - GI infections Flashcards
Define gastroenteritis
• Gastroenteritis = rapid onset diarrhoeal illness, lasting <2 weeks with diarrhoea (loose or unformed stool) ≥3/day or ≥200g of stool which is either viral or bacterial in aetiology
o Acute <14 days (may be viral or bacterial)
o Persistent 14-29 days
o Chronic >30 days (may be due to parasites and non-infectious aetiology)
Small bowel vs large bowel diarrhoea
o Small bowel diarrhoea
Watery, crampy abdominal pain, bloating and gas
Inflammatory cells, blood, fever rare
o Large bowel diarrhoea
Small volume, painful, occur with blood/mucous
Inflammatory cells + fever common
Define outbreak
> 2 cases of common food source or exposure
Diarrhoea with fever + neutrophils
Campylobacter
Shigella
Non-typhoidal salmonella
Diarrhoea with fever + mononuclear cells (enteric fever)
Yersinia
Brucella
Typhoidal Salmonella
How do toxins cause secretory diarrhoea
o Cholera toxin:
Subunit production
cAMP opens Cl- channels at the apical membrane of the enterocytes causing an efflux of Cl- to lumen with loss of water and electrolytes profoundly dehydrated
o Superantigens:
Superantigens bind directly to TCRs and MHC molecules, outside the peptide binding site there is massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response) secretory diarrhoea
What is the mechanism behind the diarrhoea seen in enteric fever?
o Inflammatory (exudative) diarrhoea
o Enteric fever – INTERSTITIAL INFLAMMATION
o Different responses in immunocompetent vs immunocompromised patients (immunocompromised patients can go into septic shock)
Suspicion of outbreak testing
Stools for bacterial, viral and parasitic infection should be tested
irrespective of blood in the stool, inflammatory markers or presence of fever or systemic symptoms
if there is suspicion of an outbreak and if tested with molecular methodology, should be followed by culture for public
ix if enteric fever suspected
stool microscopy and culture
Persistent or chronic D
Cryptosporidium spp
Giardia lamblia
Entamoeba histolytica
Bloody stool
STEC Shigella Salmonella Campylobacter Entamoeba histolytica noncholera vibrio species Yersinia
fever
any infection
higher temperatures - salmonella, Entamoeba histolytica
Persistent abdo pain + fever
Yersinia enterocolitica
Yersinia pseudotuberculosis
may mimic appendicitis
N+V lasting <24h
Staph aureus
Bacillus cereus
V + non-bloody diarrhoea 2-3d
norovirus
