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.
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)
The vast majority of patients don’t require antimicrobial treatment as management of gastroenteritis.
However, a small minority do. Which groups are antibiotics indicated for?
Immunocompromised patients
Those with severe sepsis or invasive infection
Chronic illness e.g malignancy
Summary
Gastroenteritis is common + can be diagnosed clinically
Minority of patients are admitted to hospital
Mainstay of treatment = rehydration – oral or IV
Minority of patients require antibiotics
What toxins does C.diff produce?
enterotoxin and cytotoxin
How do you treat C.diff?
metronidazole
If severe - Oral vancomycin - usually don’t take vancomycin orally because it is a big molecule and passive diffusion into the systemic circulation is less than 10%. But in this case it is good as it remains within the gut and can act on the c.diff there
Fidaxomicin (new and expensive)
Stool transplants
Surgery may be required
How can you identify salmonella in the lab?
Using MacConkey agar which contains a pH indicator – turns pink if bacteria are fermenting lactose and producing acid.
If you grow on this agar, salmonella will not show colour change as they are non-fermenters
What do S.typhi and S.paratyphi cause?
Typhoid and paratyphoid and not gastro-enteritis
How can you prevent C.diff infection?
Reduction in broad spectrum antibiotic prescribing
Avoid 4 Cs – cephalosporins, co-amoxiclav, clindamycin, ciprofloxacin
Isolate symptomatic patients
Wash hands between patients
Management of C.diff
Stop precipitating antibiotic (if possible)
Follow published treatment algorithm – oral metronidazole if no severity markers (i.e. fever, WCC >15, acute rising creatinine or suspicion of colitis/toxic megacolon)
Oral vancomycin if 2 or more severity markers
Parasites found in the UK (2)
Giardia lamblia
Cryptosporidium parvum
Parasitic diarrhoea: Giardia lamblia
Causes Giardiasis - abdominal cramps, bloating, nausea and bouts of watery diarrhoea, malabsorption and failure to thrive
Source = contaminated water
treat with metronidazole
Parasitic diarrhoea: Cryptosporidium parvum (protozoa)
Causes Cryptosporidiosis – watery diarrhoea, nausea and vomiting, abdominal cramps, low grade fever
Exist in two forms: oocysts, trophozoites
Source: ingestion of oocysts in faecally contaminated water
No specific treatment
Viral diarrhoea types (3)
Rotavirus
Adenovirus
Norovirus
What age group does Rotavirus typically affect?
Children under 5 yrs
Norovirus
Very infectious – 1g faeces may shed 5 billion infectious doses
Ward closures common – staff and patients affected
Diagnosis by PCR
Alcohol gel is not effective
Parasitic diarrhoea: Entamoeba histolytica
Imported parasite into the UK
Amoebic liver abscess may be long term complication (“anchovy pus”) – trophozoites multiply in liver cells
Which 4 antibiotics should be avoided to prevent c.diff infection?
cephalosporins, co-amoxiclav, clindamycin, ciprofloxacin
