Infectious Diarrhoea Flashcards
What is the difference between diarrhoea, gastro-enteritis and dysentery?
Diarrhoea = fluidity and frequency (subjective)
Gastro-enteritis = three or more loose stools/day with accompanying features (objective)
Dysentery = large bowel inflammation, blood stools (obvious)
What are the 7 types of stool on the Bristol stool chart?
What are some causes of gastro-enteritis?
- Contamination of foodstuff
- Poor storage of produce
- Bacterial proliferation at room temperature
- Travel related infections
- Such as salmonella
- Person to person spread
- Such as norovirus
Are viruses or bacteria the most common cause of gastro-enteritis?
Viruses
Which bacteria is the commonest bacterial pathogen for gastro-enteritis?
Campylobacter
What bacteria causes the most hospital admissions due to gastro-enteritis?
Salmonella
What are some defences against enteric infection?
- Hygiene
- Stomach acidity
- Normal gut flora
- Immunity
What are the 3 classes of clinical features of diarrhoeal illness?
Non-inflammatory/secretory
Inflammatory
Mixed
How do non-inflammatory/secretory illnesses cause diarrhoea?
- Secretory toxin-mediated
- Cholera increases cAMP levels and Cl secretion
What is an example of bacteria that causes non-inflammatory/secretory illness and diarrhoea?
- Enterotoigenic E.Coli
What is the main therapy for a non-inflammatory/secretory illness causing diarrhoea?
- Rehydration mainstay of therapy
What is an example of a bacteria causing inflammatory diarrhoeal illness?
Shigella dysentery
Describe how inflammatory illness causes diarrhoea?
- Inflammatory toxin damage and mucosal destruction
- Causing pain and fever
- Bacterial infection/amoebic dysentery
What is the treatment for inflammatory illnesses causing diarrhoea?
- Antimicrobials but rehydration alone is often sufficient treatment
Which of non-inflammatory/secretory or inflammatory illness is more associated with pain?
Non-inflammatory - frequent watery stools with little abdominal pain
Inflammatory - pain and fever
What is an example of bacteria causing diarrhoea by both non-inflammatory and inflammatory mechanisms?
C. Difficile
Describe the mechanism of diarrhoea in cholera?
- Increased cAMP results in loss of Cl from cells along with Na and K
- Osmotic effect leads to massive loss of water from gut
In what kind of diarrhoea can fluid and electrolyte loss be severe?
Fluid and electrolyte loss can be severe with secretory diarrhoea:
- Hyponatraemia due to sodium loss
- Hypokalaemia due to K loss
When assessing a patient with diarrhoea what should be explored?
- Symptoms and duration
- Risk of food poisoning
- Dietary, contact, travel history
- Assess hydration
- Postural BP, skin turgor, pulse
- Features of inflammation
- Fever, raised WCC
What are signs of poor hydration?
What investigations should be done for diarrhoea?
- Stool culture with or without molecular or Ag testing
- Blood culture
- Renal function
- Blood count
- Neutrophilia, haemolysis
- Abdominal x-ray/CT if abdomen distended or tender
What is the common differential diagnosis for infectious diarrhoea?
- Inflammatory bowel disease
- Spurious diarrhoea
- Secondary to constipation
- Carcinoma
What are indicators that the diarrhoea and fever is not due to gastro-enteritis?
Diarrhoea and fever can occur with sepsis outside of the gut:
- Lack of abdominal pain goes against gastroenteritis
- No blood/mucus in stools
What is the treatment of gastro-enteritis?
Rehydration:
- Oral rehydration with salt/sugar solution
- IV saline
What is done to identify causative organism of infectious diarrhoea?
Routine bacterial culture is done to identify causative organism, but is difficult midst complex normal flora:
- Takes 3 days to complete all tests
- Selective and enrichment methods of culture necessary
- Molecular detection
- Antigen detection
What two species of coampylobacter cause the most infections?
- C. Jejuni (90%)
- C. Coli (9%)
Where is campylobacter found?
Found in chickens, contaminated milk, puppies
Does campylobacter gastroenteritis usually occur in isolated cases or outbreaks?
Isolated cases
Describe the timing of salmonella gastroenteritis?
- Symptoms onset usually <48 hours after exposure
- Diarrhoea usually lasts less than 10 days
What 2 species of salmonella usually cause salmonella gastroenteritis?
- S. Enterica
- S. Bongori (cold-blooded animals)
- >2500 serotypes with individual names, most are S. Enterica
What are the 2 most common salmonella isolates?
- Salmonella enteritidis
- Salmonella typhimurium
How is salmonella identified as the cause of gastroenteritis?
Screen by microscope, then antigen and biochemical tests
(Screened out as lactose non-fermenters as E.coli ferments lactose and salmonella does not)
What species of salmonella cause enteric fever and not gastro-enteritis?
S.Typhi and S.Paratyphi cause enteric fever (typhoid and parathyphoid) and not gasto-enteritis
How is E-Coli 0157 spread?
Infection from contaminated meat or person to person spread
What is an E-coli 0157 infection characterised by?
Characterised by frequent bloody stools
What toxin is produced by E-coli 0157
What is a consequence of toxins from E-Coli 0157 getting into the blood?
Toxin can cause haemolytic-uraemic (HUS) syndrome, which is haemolytic anaemia and renal failure and thrombocytopenia:
- This happens because toxins stimulate platelet activation causing micro-angiopathy
- Treatment is supportive, antibiotics not indicated
What is HUS?
Haemolytic-uraemic syndrome:
- which is haemolytic anaemic, renal failure and thrombocytopenia
How do toxins from e-coli 0157 cause HUS?
This happens because toxins stimulate platelet activation causing micro-angiopathy
What is the treatment for HUS?
Treatment is supportive, antibiotics not indicated
What bacteria is usually responsible for diarrhoea?
Campylobacter
Salmonella
E. Coli 0157
Shigella
Other forms of e.coli
Staph aureus
Bacillus cereis
Clostridium perfringens
Clostridium difficile
What 4 species of shigella are known to cause diarrhoea?
S. Sonnei, S. Flexneri, S. Boydii, S. Dysenteriae
Sonnei in nurseries
What are several forms of e.coli? (4)
- Enterohaemorrhagic
- Enterotoxic (traveller’s diarrhoea)
- Enteroinvasive – organisms invade
- Enteropathogenic
- Routine diagnosis of may E. Coli strains is not possible, only 0157 as is not sorbitol fermenting whereas the rest are
What are some occasional causes of food poisoning outbreaks?
- Staph aureus (toxin)
- Bacillus cereus
- Clostridium perfringens
When are antibiotics indicated in gastroenteritis?
Indicated in gastroenteritis for:
- Immunocompromised
- Severe sepsis or invasive infection
- Chronic illness such as malignancy
Not indicated for healthy patient with non-invasive infection
Patients with C. Diff diarrhoea usually have a history of what?
Patient usually has history of previous antibiotic treatment
What is inflammation of the large intestine due to overgrowth of C. Diff called?
Pseudomembranous colitis
What toxins does C. Diff produce?
C. Diff produces enterotoxin (A) and cytotoxin (B) which are inflammatory
What are different forms of treatment for C. Diff diarrhoea?
- Metronidazole
- Oral vancomycin
- Fidaxomicin (new and expensive)
- Stool transplants
- Surgery may be required
What can be done for CDI prevention?
- Reduction in broad spectrum antibiotic prescribing
- Avoid 4Cs
- Cephalosporins
- C-amoxiclav
- Clindamycin
- Ciprofloxacin
- Antimicrobial management team (AMT) and local antibiotic policy
- Isolate symptomatic patients
- Wash hands between patients (spores resist alcohol rubs)
- Cleaning environment
What does AMT stand for?
Antimicrobial management team
What antibiotics should be avoided to avoid risking a C. Diff overgrowth?
- Cephalosporins
- Co-amoxiclav
- Clindamycin
- Ciprofloxacin
Describe the management of CDI?
- Stop precipitating antibiotics (if possible)
- Follow published treatment algorithm
- Oral metronidazole if no severity markers
- Oral vancomycin if 2 or more severity markers
What are the severity markers in CDI?
- Raised temp > 38.5
- WCC >15
- Acute rising creatinine
- Suspicion of colitis/ileus/toxic megacolon
What is responsible for parasite infections?
Protozoa and helminths
What are parasite infections generally diagnosed by?
Diagnosis generally by microscopy:
- Send stool with request “parasites, cysts and ova” or P, C and O
What are common UK parasites?
- Giardia duodenalis
- Cryptosporidium parvum
BOTH PROTOZOA
What does giardia duodenalis cause?
- Causes diarrhoea, gas, malabsorption, failure to thrive
What is giardia duodenalis transmitted by?
- Direct contact with cattle/cats/dogs/other people
- Food/water contaminated with faeces
How is giardia duodenalis infection diagnosed?
Exists as cysts (can survive outside host) and trophozoites (from the cyst)
- Cysts seen on stool microscopy
- Trophozoites – diarrhoea specimen (not normal stool specimen), duodenal biopsy or “string test” (gelatin capsule on absorbent string – swallowed and withdrawn)
What is the treatment for a giardia duodenalis infection?
- Treat with metronidazole
What does cryptosporidium parvum cause?
- Causes diarrhoea, nausea, vomiting and abdominal pain
What is cryptosporidium parvum transmitted by?
- Transmitted by infected animals/faeces, or food water
How is a cryptosporidium parvum infection diagnosed?
- Oocysts seen on microscopy
What is the treatment for a cryptosporidium parvum infection?
- No specific treatment usually required
What is a common imported parasite?
- Entamoeba histolytica
PROTOZOA
What infections can entamoeba histoytica cause?
- Different infections
- Ameobic dysentery (intestinal amoebiasis)
- Invasive extraintestinal amoebiasis (liver/pleuropulmonary/brain abscess)
What investigations are done for entamoeba histolytica infection?
- Microscopy
- Trophozoites in symptomatic patient
- Cysts in asymptomatic patient
- Antibody detection (serum) for invasive disease
What is the treatment for entamoeba histolytica infection?
- Metronidazole and luminal agent to clear colonisation
What is viral diarrhoea often caused by?
- Rotavirus
- In children under 5
- Vaccine exists for children at 8 and 12 week (70% reduction)
- Norovirus
- Most common cause of outbreaks
- Common in
- Hospitals, schools, care homes, cruise ships, prisons
- Diagnosis by PCR
- Adenovirus
In what season is viral diarrhoea most common?
Winter
How is viral diarrhoea diagnosed?
Diagnosis by antigen detection in stool
What are the general rules for treating a patient with gastro-enteritis?
- Not indicated for healthy patient with non-invasive infection
- Campylobacter – macrolides (clarithromycin)
- Salmonella – ciprofloxacin, some are resistant
- Mainstay of treatment – rehydration, can be done with oral rehydration solution
