Micro 12 - GI infections Flashcards
(34 cards)
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
D+ abdo cramping 1-2d
Clostridium perfringens
Bacillus cereus
Extra-intestinal manifestations causative organisms
o aortitis, osteomyelitis, deep tissue infection o haemolytic anaemia o Glomerulonephritis o HUS o erythema nodosum o reactive arthritis o meningitis
o Salmonella, Yersinia aortitis, osteomyelitis, deep tissue infection
o Campylobacter, Yersinia haemolytic anaemia
o Shigella, Campylobacter, Yersinia Glomerulonephritis
o STEC, Shigella HUS
o Yersinia, Campylobacter, Salmonella, Shigella erythema nodosum
o Salmonella, Shigella, Campylobacter, yersinia, (giardia, Cyclospora cayetanensis) reactive arthritis
o Listeria, salmonella (infants <3m) meningitis
Staph aureus - how does it cause diarrhoea
Produces enterotoxin - can acts as a super antigen in the GIT, releasing IL1 IL2 –> vomiting + watery non bloody diarrhoea
C difficile - how does it cause diarrhoea
produces 2 toxins - toxin A and toxin B
Toxin A - enterotoxin - inflammation
Toxin B - cytotoxin - virulence factor (more dangerous than A)
Which organism can cause paralysis and how?
Clostridium botulinum
from canned or vacuum packed food
ingestion of preformed toxin –> blocked release of ACh from PNS - paralysis
Listeria buzzwords
b haemolytic
aesculin positive
tumbling-weed motility
refrigerated foods
unpasteurized dairy
vegetables
mx - amoxicillin
What causes travellers diarrhoea and how to manage it
E coli
Dont give abx
Enterotoxins produced in traveller’s diarrhoea
caused by E. coli
Heat labile enterotoxin – adenylate cyclase + cAMP
Heat stable enterotoxin – stimulates guanylate cyclase
bowel (jejunum/ ileum) not on colon
E coli vs salmonella vs shigella vs vibrio vs yersinia
E coli
glucose/lactose fermenters
Salmonella
non-lactose fermenters
H2S producers
Shigella
non-lactose fermenters
non H2S producers
vibrio
late lactose fermenter
Yersinia
non lactose fermenter
