Diarrhoea Flashcards
What are the three main bacteria that are sought by routine cultures of stools?
- Campylobacter
- E. coli O157
- Salmonella
describe the incubation prossess Campylobacter?
○ Up to 7 days incubation so dietary history may be unreliable
○ Stools negative within 6 weeks
○ abdominal pain can be severe
○ <1% invasive
What is the post infective sequelae of campylobacter?
Guillain-Barre syndrome, Reactive arthritis
What is the routine bacterial culture of Campylobacter?
- specialised culture conditions
- C. jejuni/ C. coli
Describe the natural history of Salmonella
○ symptom onset usually <48 hrs after exposure
○ diarrhoea usually lasts <10 days
○ <5% positive blood cultures
○ 20% patients still have positive stools at 20/52
○ Prolonged carriage may be associated with gallstones
○ Post-infectious irritable bowel is common
What is the routine bacterial culture of Salmonella?
- screened out as lactose non-fermenters - then antigen and biochemical tests
- thousands (!) of species with individual names
- genetically most are serotypes of the same species (Salmonella enterica)
- traditionally named after place of first isolation
- Commonest isolates are Salmonella enteritidis and Salmonella typhimurium
- > 50% of these were imported from abroad in 2010
- N.B. - S. typhi and S. paratyphi cause enteric fever (typhoid and paratyphoid) and not gastro-enteritis
How does E. coli O157 spread and how is the illness typically characterised?
○ Infection from e.g. contaminated meat or person-to-person spread (low inoculum)
○ Typical illness characterised by frequent bloody stools
What are the other bacteria that cause diarrhea?
• Shigella (4 species) – outbreaks of Shigella sonnei in nurseries
• several other forms of E. coli cause diarrhoea
• enteropathogenic
• enterotoxic (traveller’s diarrhoea)
• enteroinvasive
• Occasional causes of food poisoning outbreaks
○ Staph aureus (toxin)
○ Bacillus cereus (re-fried rice)
○ Clostridium perfringens (toxin)
How would you diagnose E. Coli (other than O157)?
• Routine diagnosis of these E. coli strains not possible – only O157 is easily distinguished from “ordinary” E. coli
List the parasites commonly detected in stool specimens in the UK
- Protozoa and helminths
- Giardia lamblia
- Cryptosporidium parvum
- Entamoeba histolytica - amoebic dysentery
What is the epidemiology of Cryptosporidium parvum?
○ first recognised in AIDS ○ contaminated water (animal faeces) ○ cysts seen on microscopy ○ no specific treatment usually required ○ 442 cases in Scotland in 2011
What is Entamoeba histolytica?
○ vegetative form in symptomatic patient - (“hot stool”)
○ cysts seen in asymptomatic patient
○ amoebic liver abscess may be long term complication (“anchovy pus”)
○ treat with metronidazole
What are the common viral causes of Diarrhea in the UK?
- Retrovirus
- Norovirus
- Adenovirus
What is the epidemiology of Retrovirus?
- rotavirus in children under 5 years
- common in winter
- diagnosis by antigen detection
- 1465 laboratory reports in Scotland in 2011
- Routine vaccination 2013
What is the epidemiology of norovirus?
○ Winter vomiting disease ○ common cause of outbreaks § hospital, community, cruise ships ○ In Scotland in 2011: § 1668 laboratory reports § 175 recorded outbreaks ○ diagnosis by PCR ○ very infectious ○ ward closures common – staff and patients affected ○ strict infection control measures needed
Define diarrhea, Gastroenteritis and dysentry
• Diarrhoea - subjective ○ fluidity and frequency • Gastro-enteritis - objective ○ three or more loose stools/day ○ accompanying features • Dysentery – obvious ○ large bowel inflammation, bloody stools
How is bacterial and viral gastroenteritis spread?
• Contamination of foodstuffs
○ e.g. chicken and campylobacter
• Poor storage of produce
○ E.g. Bacterial proliferation at room temperature
• Travel-related infections e.g. Salmonella
• Person-to-person spread
○ e.g. norovirus
What are the trends with bacterial and viral gastroenteritis?
- 25% of population have Infectious intestinal disorder each year
- 2% of population visit GP because of GI infection each year
- For each reported case there are 10 GP consults and 147 community cases that are unreported
- Viruses are commonest cause with campylobacter being the commonest bacterial pathogen
What are the food poisoning trend?
○ There are more than 500,000 cases of food poisoning a year from known pathogens
○ Campylobacter is the most common foodborne pathogen, with about 280,000 cases every year
○ Salmonella is the pathogen that causes the most hospital admissions – about 2,500 each year
○ Poultry meat was the food linked to the most cases of food poisoning, with an estimated 244,000 cases every year
How should someone assess a patient with gastroenteritis?
○ Symptoms and their duration - >2/52 unlikely to be infective gastroenteritis ○ Risk of food poisoning - Dietary, contact, travel history ○ assess hydration - postural BP, skin turgor, pulse ○ features of inflammation (SIRS) - fever, raised WCC
Describe the fluid and electrolyte loss in a patient with gastroenteritis?
○ Can be severe with secretory diarrhoea
- 1-7 l fluid per day containing 80-100 mmol Na
- Hyponatraemia due to sodium loss with fluid replacement by hypotonic solutions
- Hypokalemia due to K loss in stool (40-80 mmol/l of K in stools)
What investigations should be carried out on a patient with gastroenteritis?
○ stool culture ○ blood culture ○ Renal function ○ blood count - neutrophilia, haemolysis ○ abdominal X-Ray if abdomen distended, tender
What are the indications to give antibiotics to a patient with gastroenteritis?
- immunocompromised
- severe sepsis or invasive infection
- valvular heart disease
- chronic illness
- diabetes
What are the complications of E. coli O157?
• Complications are caused by the toxin (not the bug) getting into your blood
• E. coli O157 produces verocytotoxin
• E. coli O157 stays in the gut but the toxin gets into the blood
• toxin can cause hemolytic-uraemic (HUS) syndrome (haemolytic anaemia and renal failure)
○ HUS characterised by renal failure, haemolytic anaemia and thrombocytopenia
○ Toxin binds to globotriaosylceramide
○ Platelet activation stimulated
○ micro-angiopathy results
○ attach to endothelial, glomerular, tubule and mesangial cells
What is the treatment for the complications of E. coli O157?
Treatment supportive – antibiotics NOT indicated
What is the commonest cause of bacterial food poisoning in UK?
Campylobacter
Through what sources can Campylobacter be transmited?
chickens, contaminated milk, puppies
Which is more common in Campylobacter: isolated cases or outbreaks?
Isolated cases
What are the host’s natural defences against enteric
Infections?
• hygiene • stomach acidity ○ antacids and infection • normal flora ○ Cl. difficile diarrhoea ○ Protect against all forms of bacterioentrities • immunity ○ HIV- salmonella
Describe the mechanisms by which infecting organisms can produce diarrhoea
• Secretory toxin-mediated
○ cholera - increases cAMP levels and Cl secretion
○ enterotoxigenic E. coli (travellers’ diarrhoea)
What are the treatments for gastroenteritis?
○ Rehydration - iv or oral?
- Oral rehydration with salt/sugar solution - iv saline
