Lecture 1: Infectious Diarrhoea Flashcards
what is dysentry?
large bowel inflammation, bloody stools
what ways can a person get gastro-enteritis?
- 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
what pathogens are the most common cause of gastroenteritis?
- viruses are most common cause
- campylobacter is the most common bacterial pathogen
what is the most common pathogen causing hospital admissions with food poisoning?
salmonella
list the defences against enteric infections
- hygiene
- stomach acidity: antacids and infection
- normal gut flora: C.diff diarrhoea
- immunity: HIV + salmonella
what are the different types of diarrhoea?
- non-inflammatory/secretory
- inflammatory
- mixed picture
features of non-inflammatory/secretory diarrhoea
what causes it, how does it present, whats the treatment
- toxin-mediated usually e.g. cholera and E.coli
- watery stools, rapid dehydration, relatively little abdo pain
- rehydration mainstay of treatment
features of inflammatory diarrhoea
what causes it, how does it present, whats the treatment
- bacterial infection usually e.g. shigella dysentery
- abdo pain, bloody stools, systemic upset
- rehydration and (sometimes) antimicrobials required
what organism typically causes diarrhoea with a mixed-picture i.e. non-inflammatory (secretory) and -inflammatory?
C.difficile
which organsims commonly cause non-inflammatory diarrhoea?
- cholera
- E.coli
how does cholera cause diarrhoea?
- 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.
how would we assess a patient with diarrhoeal illness?
- 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
describe the fluid and electrolyte losses due to diarrhoeal illness
- 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)
diarrhoeal illness investigations
- 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
features of campylobacter gastroenteritis
- 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
which two species of campylobacter cause the most infections?
C.jejuni (90%)
C.coli (9%)
sources of Campylobacter infection
- chickens
- contaminated milk
- puppies
del
Features of E.coli O157:H7
- 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
features of Shigella infection
- 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
features of Traveller’s diarrhoea
- 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
features of viral gastro-enteritis
- 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.
list some intestinal parasites
- Cryptosporidiosis
- Giardia
- entamoeba histolytica
gastroenteritis diagnostic requirements
- 3+ stools in 24 hours plus at least one of fever, vomiting, pain, blood/mucus stools
features of Cryptosporidiosis
- 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
features of Giardia
- present in surface water
- asymptomatic cyst carriers
- treatment by metronidazole, tinidazole
features of Entamoeba histolytica
- microscopy only 50% sensitive
- may mimic ulcerative colitis
- treat symptomatic disease with 10/7 metronidazole and furamide for cyst carriage
what % of patients given antimicrobials get diarrhoea?
5-10%
C.difficile is present in what percentage of antibiotic associated diarrhoea (AAD)? AND WHY?
10-15%
overgrowth of C.diff and production of toxins A > enterotoxin and B > cytotoxin
antibiotic associated diarrhoea (AAD) treatment
- metronidazole (up to 6% resistant, poor stool concn.)
- vancomycin (cost and drug resistance in gut flora)
- teicoplanin/fusidic acid/cholestyramine
- surgery
commonest salmonella isolates in the UK
- salmonella enteriditis
- salmonella typhimurium
HUS is characterised by
- renal failure
- haemolytic anaemia
- thrombocytopenia
list some occasional causes of food poisoning outbreaks
- Staph aureus (toxin)
- Bacillus cereus (re-fried rice)
- Clostridium perfringens (undercooked meat/cooked food left out - toxin accumulates in spore formation)
when are antibiotics indicated for gastroenteritis
- immunocompromised
- severe sepsis or invasive infection
- chronic illness e.g. malignancy
- not indicated for healthy hapteint with non-invasive infection
treatment for C.diff diarrhoea
- metronidazole (if no severity markers)
- oral vancomycin (if 2 or more severity markers)
- fidaxomicin (new and expensive)
- stool transplants
- surgery may be required
how can C.diff infection be prevented?
- 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
how is norovirus diagnosed?
PCR
list the bacterial species that are routinely sought in stool specimens
- campylobacter
- salmonella
- shigella
- e.coli O157
- cholera (under specific circumstances)
