GI Infections Flashcards
What is gastroenteritis?
A rapid onset diarrheal illness, lasting less than 2 weeks with diarrhoea (loose and unformed stool) three or more times a day or at least 200 g of stool which is either viral or bacterial in aetiology.
What are reportable GI infections?
Campylobacter
Salmonella
Shigella
E.Coli 0157
Listeria
Norovirus
What is the incubation period, duration and cause of Campylobacter?
Incubation: 1-10 days
Duration: 2-20
Cause: Poultry
What is the incubation period, duration and cause of E.Coli 0157?
Incubation: 1-5 days
Duration: 1-4
Causes: HUS, verotoxin
What is the incubation period and duration of Shigella?
Incubation period: 12-96hrs
Duration: 5-7
What is the incubation period and duration of Salmonella (non-typhoidal)?
Incubation: 8-48h
Duration: 4-7
What is the incubation period and duration of Vibrio parahaemolyticus?
Incubation: 24-72h
Duration: 2-10
What are the mechanisms of disease for GI infections?
Secretory diarrhoea - toxin production: Cholera toxins and superantigens
Inflammatory diarrhoea vs enteric fever
How do cholera toxins lead to diarrhoea?
cAMP: opens Cl channel at the apical membrane of enterocytes.
Leads to efflux of Cl to lumen; loss of H2O and electrolytes.
How do superantigens lead to diarrhoea?
Superantigens bind directly to T-cell receptors and MHC molecules outside the peptide binding site.
This leads to massive cytokine production by CD4 cells ie systemic toxicity and suppression of adaptive response.
What is Staph. Aureus food poisoning?
1/3 population chronic carriers, 1/3 transient
Spread by skin lesions on food handlers.
Catalase, coagulase positive Gram positive coccus.
Appears in tetrads, clusters on Gram stain
Yellow colonies on blood agar
What is this?
Staph. Aureus on blood agar
What is the pathogenesis of Staph. Aureus food poisoning? What is the treatment of Staph. Aureus food poisoning?
Produces enterotoxin, an exotoxin that can act as a superantigen in the GI tract, releasing IL1 and IL2, causing prominent vomiting and watery, non bloody diarrhoea.
Don’t treat, self limited.
What is the pathogenesis of Bacillus cereus food poisoning?
Gram positive rod-spores
Heat stable emetic toxin: Not destroyed by reheating.
Heat labile diarrhoeal toxin: Food is not cooked to a high enough temperature.
What is this?
Bacillus cereus
What are clinical features of Bacillus cereus food poisoning?
Watery non bloody diarrhoea; self limited
Rare cause of bacteremia in vulnerable population
Can cause cerebral abscesses
What is clostridia?
Gram Positive Anaerobe
What is Clostridium botulinum food poisoning?
Botulism
Source: Canned or vacuum packed food (honey/infants)
Ingestion of preformed toxin (inactivated by cooking)
Blocks Ach release from peripheral nerve synapses
Treatment with antitoxin
What is Clostridium pefringens food poisoning?
Source: Reheated food (meat)
Normal flora of colon but not small bowel, where the enterotoxin acts (superantigen)
Incubation 8-16hrs
Watery diarrhoea, cramps,little vomiting lasting 24hrs
What is Clostiridium difficile (Pseudomembranous colitis)?
3%, 30% of hospitalised patients
Antibiotic related colitis (any but mainly cephalosporins, cipro and clindamycin).
What is the treatment of C.Diff?
Oral vancomycin
Adjunct: IV Metronidazole
What is Listeria monocytogenes food poisoning?
Outbreaks of febrile gastroenteritis.
ß haemolytic, aesculin positive with tumbling motility.
Source: Refrigerated food (“cold enhancement”),i.e. unpasteurised dairy, vegetables.
Grows at 4 ºC GI watery diarrhoea, cramps, headache, fever, little vomiting.
Perinatal infection, immunocompromised patients.