Infectious diarrhoea Flashcards
What is Gastroenteritis?
inflammation of the stomach and intestines, typically resulting from bacterial toxins or viral infection and causing vomiting and diarrhoea.
How is diarrhoea defined?
3 or more loose or watery stools per day
faeces that fits the receptacle it is in
What are the pathological mechanism of diarrhoea?
- toxin mediated
- damage to intestinal epithelial surface
- invasion across intestinal epithelial barrier
How can toxins be produced?
o Produced prior to consumption (S.aureus, B.cereus)
- Toxins are liberated onto food by the bacteria before the food is consumed
- Hallmark = sickness a few hours after eating
o Produced after consumption (C.difficile, E.coli 0157)
- Once consumed, the organism replicates within the gut and produces toxins
How can epithelial damage cause diarrhoea?
o Direct toxic effect to cells
o Inflammation of the gut causes diarrhoea = gut tries to evacuate the pathogen
What are the three main symptoms to look for in a patient presenting with diarhoea
- vomiting
- type of diarrhoea
- non-intestinal manifestations
What is the significance of vomiting in a patient with diarrhoea
(nausea common, vomiting uncommon)
o Sudden onset within 6-12hrs of food ingestion suggests pre-formed toxin (in food)
S. aureus
B. cereus - e.g. in contaminated rice
o Viral aetiology
Norovirus
Sapovirus
How can diarrhoea be classed?
classified according to where the predominant infection is:
- small intestine
- large intestine
What are the symptoms associated with small intestine diarrhoea?
(digestion and absorption) infection will result in:
o high volume diarrhoea
o a lot of cramping (stretching of small intestine)
o weight loss when chronic (due to impaired nutrient absorption)
o bloating
o wind
What are the symptoms of large intestine diarrhoea?
= (fluid and electrolyte absorption) colitis: o frequent diarrhoea o small amounts o Often contains blood o Fever o Painful stool
What are the most common bacterial causes of diarrhoea?
Campylobacter sp – by far the most common bacterial cause of gastroenteritis
Salmonella sp – battery hens are vaccinated against salmonella, greatly reducing prevalence
Shigella sp – often seen in travellers
E. coli (0157: H7)
Clostridium difficile
What are the most common viral causes of diarrhoea?
Norovirus
Sapovirus
Rotavirus – common cause of D&V in children
Adenoviruses – red eye, vomiting, diarrhoea
What are the most common parasitic causes of diarrhoea?
Cryptosporidium – causes small bowel infection
o Colonises the gut of lambs – common in lambing season (infects water supply from faeces
washout)
Giardia – travel related
Entamoeba histolytica – LI infection, travel related
Cyclospora - travel related (often seen in Mexico)
Isospora - travel related
What should be enquired during a history of a patient with diarrhoea?
- Food history
- Onset & nature of symptoms
- Residence
- Occupation
- Travel
- Pets / hobbies
- Recent hospitalisation / antibiotics
- Co-morbidity
What is the use of Faecal leukocytes & occult blood testing?
Both a waste of time, not used clinically at all in the UK
(idea is that presence of faecal leukocytes may indicate a colonic or “inflammatory” cause
o Poor sensitivity & specificity
o Not used clinically
Faecal occult blood
o Bacterial cause
Faecal calprotectin
o Protein found in stool that can be elevated with inflammation in the gut
o Can be raised but NOT specific for infection
What is the use of obtaining a stool culture?
Necessity of documenting a pathogen
o Self-limiting illness
o Indications for treatment – whether or not to give antibiotics
o Public health implications – limiting spread of infection (e.g. preventing people from handling
food while infected)
Consider microscopy for ova and cysts if parasitic cause is possible
o Travellers
o Epidemiology
What are the disadvantages of stool cultures?
Low rate positive stool cultures (1.5-5.6% of patients)
o Viral causes cannot be cultured
o Organisms in the gut are used to very specific environmental conditions, and this is incredibly
difficult to reproduce in the lab
o Campylobacter is very difficult to culture
o Many patients will therefore have a false negative
What is the use of endoscopy in patients with diarrhoea?
Not very useful, as it does not add to diagnosis with infective diarrhoea
Can indicate colitis, but not the source of infection
Useful when patient has diarrhoea but no infection can be used to rule out disorders of the gut, e.g.
UC/Crohn’s with biopsies
How is infectious diarrhoea treated?
Oral rehydration solution – morbidity can result from dehydration
o Small intestinal Na-glucose cotransport remains intact
o Can absorb water if Na & glucose also present (osmotic potential)
May require IV fluid replacement
o Vomiting
Should antibiotics be given to patients with diarrhoea?
Self-limiting illness – antibiotics are usually not required
Antibiotics reduce duration of diarrhoea by about 1 day (1.7 v 2.8 days)
o This is not worth the damage antibiotics do to the patient or the risk of antibiotic resistance
Antibiotics can WORSEN outcome in some illnesses
o E. coli 0157:H7
Which patients should receive antibiotics?
- v. ill
- septic/ evident bacteraemia
- significant co-morbidity
- certain causes
What cause of diarrhoea should be given antibiotics and what antibiotic should be given?
C. difficile associated diarrhoea (metronidazole)
What is the use of treating symtpoms of diarrhoea?
e.g. Imodium
Generally not indicated
Potentially worsens prognosis in bacterial disease but may be safe given with antibiotics for travellers
Diarrhoea is the body’s way of eliminating the organism
Slowing this down may prolong the duration of illness
In what situations can exclusion diets be helpful?
o Could potentially be beneficial in managing C.difficile infection
o Travellers diarrhoea = cutting out lactose helps with giardia infection
What is the common cause of Campylobacter diarrhoea?
Most common source is chicken
What is the pathophysiology of campylobacter diarrhoea?
Infecting dose of ~9000 organisms Sensitive to stomach acidity o Beware things that reduce stomach acidity, e.g. PPIs = increase susceptibility to infection Attach and invade intestinal epithelial cells o Small bowel o Large bowel o Causes mixed diarrhoea Incubation period 3 days (1 to 7 days) o Depends on infecting dose
What are the clinical features of campylobacter diarrhoea?
Diarrhoea o Frequent and can be high volume o Blood in stool common Abdominal pain (cramping) Often severe Nausea common / vomiting rare Fever
How is campylobacter diarrhoea managed?
Clinical course
o Self-limiting (7 days)
Antibiotics usually not given, rarely indicated
o High rates of antibiotic resistance
o Can develop resistance to the antibiotic used on treatment
What are late complications of campylobacter diarrhoea?
o Reactive arthritis
o Guillain-Barre
What is the main source of SALMONELLA diarrhoea?
Main source = chicken, reptiles (excrete salmonella on their skin)
Spreads person-to- person
Describe the pathophysiology of salmonella diarrhoea
Numerous serotypes, but generally split into:
o Typhoidal (travellers)
o Non-typhoidal
Infectious dose ~10,000 organisms
Interactions with host
o Increased risk with decreased stomach acid (PPIs, H2RA, etc.)
o Increased risk with diminished gut flora
Invasion of enterocytes with subsequent inflammatory response
o Can cause bacteraemia/systemic infection
What are the clinical features of salmonella diarrhoea
Illness within 72 hours of ingestion
Onset of illness depends on inoculum; higher inoculum more rapid onset
Nausea, diarrhoea, abdominal cramps, fever
Invasive disease
o Bacteraemia in <5%
o Secondary infection (endocarditis, osteomyelitis, mycotic aneurysm)
How should salmonella diarrhoea be treated?
NB: when patients with gastroenteritis are treated with antibiotics its normally because of the fear of invasive salmonella Antibiotics o Self-limiting (up to 10 days) o No significant reduction in duration o Severe disease
What are the public health implications of salmonella diarrhoea?
Clear implications for food handlers (due to person-person transmission)
o Asymptomatic shedding common & episodic
o Median 5 weeks
o Negative stool cultures (>1)
What is the main source of e.coli 0157
Found in beef mince, but also in vegetables (bean sprouts, spinach) because of fertiliser (animal faeces)
Person-person transmission
Commonly caught at petting zoos
Excreted by animals with more than one stomach
What is the pathogenesis of e.coli 0157
Attachment to large bowel Shiga toxin production o Enterocyte death o Enters systemic circulation Infectious load as little as 10 organisms – incredibly infectious Sporadic outbreaks
What are the clinical features of e coli 0157
Incubation period 3 to 4 days
Bloody diarrhoea & abdominal tenderness
Fever is rare
> Haemolytic Uraemic Syndrome
What is Haemolytic Uraemic Syndrome?
Systemic effect of shiga toxin
Triad of:
o Microangiopathic haemolytic anaemia (formation of fibrin clots in small blood vessels => RBC
sheared open when they pass)
o Acute renal failure (most small blood vessels in the kidney)
o Thrombocytopenia (because platelets used in the clots)
What is the incidence of Haemolytic Uraemic Syndrome?
Only occurs in up to 9% patients
Tends to come on 5 to 10 days after onset diarrhoea
o Diarrhoea may already have cleared
How is Haemolytic Uraemic Syndrome treated?
50% require dialysis o Mortality 3 to 5% o Association with antibiotics Poorer outcome with antibiotics Management o Supportive, elimination of toxin (dialysis etc.)
Prevention is key o Strict infection control for healthcare workers o Screening of contacts o Appropriate butchering of meat o Public health measures in outbreaks
What are the risk factors for clostridium difficile infection?
- antibiotic exposure
- older age (>65 - ?PPI use)
- hospitalisation
Elderly are at higher risk because gut microbiota decreases with age
Describe the pathogenesis of clostridium difficile infection?
Destruction of gut microbiota allows colonisation by other bacteria => toxin production
What are the symptoms of clostridium difficile infection?
Loose stool & colic
Fever
Leukocytosis – because it is toxin-mediated
Protein losing enteropathy – any condition of the GI tract that results in a net loss of protein from the body (e.g. damage to the gut wall)
Pseudomembranous colitis – masses of puss on surface of colon
How is C diff detected?
Toxin detection via:
- tissue culture assay (no longer commonly used)
- c. diff antigen/ c. diff toxin
first test for antigen, then test for toxin
How is c. diff treated?
Stop causative antibiotics if possible (or at least narrow spectrum)
o Allows normal gut flora to grow back
Metronidazole / Vancomycin
Faecal transplant - recolonise with normal flora
o 96% cure rate
Describe norovirus
Norovirus most common cause of epidemics
o Tends to cause outbreaks within institutions (hospitals, care homes, nurseries, etc.)
o Can lead to hospital ward closure
Occur in all months with peak in winter
How is norovirus transmitted?
o Faecal oral route
o Infectious dose 10 – 100 viruses
o Very stable organism (can survive up to 60°C, bleach, and utterly resistant to alcohol gel)
Must wash hands with soap and water, physically wash the virus off
What are the clinical features of norovirus?
o Acute explosive diarrhoea and vomiting
o Causes illness within 24 – 48 hours
o No lasting immunity
