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
