Infectious diarrhoea Flashcards
Definition of gastroenteritis
Three or more loose stools/day
Accompanying features – abdominal pain, fever, vomiting, blood/mucus in the stool
Definition of Dysentery
Large bowel inflammation
(+ a lot of abdominal pain), bloody stools
this is an old term but is still used sometimes
Causes of gastro-enteritis
Contamination of foodstuffs - Intensively farmed chicken and campylobacter
Poor storage of produce -
Bacterial proliferation at room temperature
Travel-related infections e.g. Salmonella
Person-to-person spread - norovirus
Which is the most common food-borne pathogen?
Campylobacter
Which pathogen causes the most hospital admissions each year?
Salmonella
What defences do we have against infections? (4)
Hygiene
Stomach acidity
Normal gut flora
Immunity
What are the 2 main presentations of gastroenteritis?
- Non-inflammatory/secretory gastroenteritis
- Inflammatory gastroenteritis
It can also be a mix of the two i.e. C.difficile
How does non-inflammatory gastroenteritis present?
Cholera and E.coli produce toxins causing this.
Frequent watery stools – not caused by inflammation. These patients are losing a lot of fluid – rehydration treatment
Mechanism of diarrhoea in cholera
Increased cAMP results in loss of Cl from cells along with Na and K
If you lose salt, you lose water with it => Osmotic effect leads to massive loss of water from the gut
How does inflammatory gastroenteritis present?
Toxins produced by the pathogens cause damage/destruction to the mucosal layer resulting in abdominal pain and fever (systemic inflammatory response)
Bacterial infection may be present.
Antimicrobials may be appropriate but rehydration alone is often sufficient
How would you assess a suspected gastroenteritis patient?
Find out their symptoms and their duration
>2/52 unlikely to be infective gastro-enteritis
Risk of food poisoning - Dietary, contact, travel history
Assess hydration - postural BP, skin turgor, pulse
Infants - sunken frontanelles, eyes or cheeks, dry mouth or tongue and few or no tears
Features of inflammation (SIRS) - fever, raised WCC
Fluid and electrolyte losses can be severe with secretory diarrhoea. What could result?
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)
Investigations for gastroenteritis patient
Stool culture +/- molecular or Ag testing (detect toxins)
Blood culture
Renal function
Blood count
Abdominal X-ray/CT if abdomen is distended, tender
What is spurious diarrhoea?
Commonly seen in care home patients.
It’s diarrhoea as a result of constipation – fluid that can get beyond the constipated stool. Easy to diagnose if you do a rectal examination
Campylobacter gastroenteritis
Up to 7 days incubation so dietary history may be unreliable
Stools negative within 6 weeks - Doesn’t hang around in your bowel
Abdominal pain can be severe
Post-infection sequelae - long term complication of acute infection - such as gastrointestinal disorders, neurological disorders, and joint disorders.
How do scientists in the lab identify specific pathogens within faecal sample etc?
Use selective and enrichment methods of culture - variety of media and incubation conditions
Culture conditions suitable for growth of Campylobacter?
Very particular culture conditions:
Temperature range 37-42 degrees and much lower O2 levels
Salmonella gastroenteritis
Symptom onset usually <48 hrs after exposure / consumption
Diarrhoea usually lasts <10 days
Stays around in your gut
Post-infectious irritable bowel is common
What can carry salmonella and cause you to be a source of infection for others over a prolonged period?
Gallstones - they can shed salmonella unless removed
2 common salmonella species?
S.enterica
S.bongori
2 common species of campylobacter?
C. jejuni
C. coli
What toxin does E.coli 0157 produce?
Shiga toxin
What is E.coli 0157?
A serotype of E.coli (there are many others but only O157 is easily distinguished from “ordinary” E.coli).
The shiga toxin that it produces causes the problem.
Infection from e.g. contaminated meat or person-to-person spread (low incoulum)
Typical illness characterised by frequent bloody stools, abdominal pain but no significant fever
The toxin can also cause Haemolytic-uraemic syndrome
What is Haemolytic-uraemic syndrome?
The toxin causes platelets to clump in the blood vessels. RBC squeeze through these clumps and become haemolysed
Results in renal failure, haemolytic anaemia and thrombocytopenia. Treatment supportive – antibiotics NOT indicated as although they destroy the organism, this releases more toxins into the bloodstream.
