Introduction to Infection and Diarrhoea Flashcards
Define gastro-enteritis - objective
–three or more loose stools/day
accompanying features
Diarrhoea is subjective - fluidity and frequency
Define dysentery
–large bowel inflammation, bloody stools
What is the epidemiology of gastroenteritis?
•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 is the most common cause of gastroenteritis?
Viruses are the commonest cause
Campylobacter is the commonest bacterial pathogen
What strain of Ecoli is assocaited with gastroenteritis?
Ecoli O157
What are the defenses against enteric infections?
- hygiene
- stomach acidity
–antacids and infection
•normal flora
–Cl. difficile diarrhoea
•immunity
–HIV- salmonella
What type of diarrhoeal illness is cholera?
Non-inflammatory/secretory
What type of diarrhoeal illness is shigella dysentery?
Inflammatory
What type of diarrhoeal illness is C.Difficile?
Mixed picture
What causes non-inflammatory diarrhoea?
–secretory toxin-mediated
- cholera - increases cAMP levels and Cl secretion
- enterotoxigenic E. coli (travellers’ diarrhoea)
frequent watery stools with little abdo pain
What is the mainstay of therapy for non-inflammatory diarrhoeal illness?
–rehydration mainstay of therapy
What causes inflammatory diarrhoea?
Bacterial infection
Amoebic dysentery (marked by dysentery, abdominal pain, and erosion of the intestinal wall)
What are the clinical features of inflamamtory diarrhoeal illness?
PAIN
FEVER
Inflammatory toxin damage and mucosal destruction
What is the mainstay of treatment for inflammatory diarrhoeal illness?
–antimicrobials may be appropriate but rehydration alone is often sufficient
What does a history of symptoms of gastroenteritis longer than 2 weeks suggest?
Unlikely to be infective gastro-enteritis
How do you assess the patient with diarrhoea?
•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
•features of inflammation (SIRS)
–fever, raised WCC
Baby may have sunken fontanelle, eyes and cheeks. Few or no tears. Dry mouth and tongue. Decreased skin turgor
Assess electrolytes and fluid losses:
Hyponatraemia due to fluid replacement with hypotonic solutions
Hypokalaemia due to K loss in stool
Investigations:
- Stool culture
- Blood culture
- Renal function
- Blood count - neutrophilia, haemolysis
- Abdominal X-Ray if abdomen distended, tender
What is the differential diagnosis for gastroenteritis?
- Inflammatory bowel disease
- Spurious diarrhoea -secondary to constipation
- Carcinoma
- Diarrhoea and fever can occur with sepsis outside the gut
- lack of abdo pain/tenderness
goes against gastroenteritis - no blood/mucus in stools
•Rehydration - iv or oral?
–Oral rehydration with salt/sugar solution
–iv saline
What is the progression of campylobacter gastroenteritis?
7 days incubation period - dietary history may be unreliable
Stools negative within 6 weeks
SEVERE abdominal pain
Less than 1% becomes invasive
Post infection sequale includes guillain-barre syndrome and reactive arthritis
What is the progression of disease for salmonella gastroenteritis?
–symptom onset usually <48 hrs after exposure
–diarrhoea usually lasts <10 days
–<5% positive blood cultures (more invasive than campylobacter)
–20% patients still have positive stools at 20/52
•Prolonged carriage may be associated with gallstones
–Post-infectious irritable bowel is common
Do salmonella bacteria ferment lactose?
NO - McConkey agar is pale after culture
What are the commonest isolates of salmonella?
Salmonella enteritidis
Salmonella typhimurium
What isolates cause typhoid?
•S. typhi and S. paratyphi cause enteric fever (typhoid and paratyphoid) and not gastro-enteritis
How is E.coli O157 spread?
From contaminated meat or person-to-person spread
What toxin does E.coli produce?
Verocyto toxin
Important to note that the toxin can get into the blood but the bacteria can’t
What is a common presenting symptom of E.coli O157?
Bloody stools
What is a risk associated with E.coli O157?
Can cause haemolytic-uraemic syndrome (HUS)
–HUS characterised by renal failure, haemolytic anaemia and thrombocytopenia. Treatment supportive – antibiotics NOT indicated
antibiotics may cause lysis of lots of cells and release dangerous amounts of toxins into the blood?
What are some other bacteria that cause gastroenteritis?
- Shigella (4 species) – outbreaks of Shigella sonnei in nurseries
- several other forms of E. coli cause diarrhoea
enteropathogenic
enterotoxic (traveller’s diarrhoea)
enteroinvasive
•routine diagnosis of these E. coli strains not possible – only O157 is easily distinguished from “ordinary” E. coli
Occasional causes of food poisoning outbreaks
- Staph aureus (toxin)
- Bacillus cereus (re-fried rice)
- Clostridium perfringens (toxin)
When are antibiotics indicated in gastroenteritis?
–immunocompromised
–severe sepsis or invasive infection
–valvular heart disease
–chronic illness
–diabetes
Not indicated for healthy person with non-invasive infection
Which antibiotics are classically associated with c diff?
4 C’s:
Cephalosporins
co-amoxiclav
clindamycin
clarithromycin
What are the consequences of c diff infection?
Mild diarrhoea
Severe colitis (pseudomembranous colitis)
What are the toxins that c diff produces?
enterotoxin (a)
cytotoxin (b)
What is the treatment of c diff infection?
Metronidazole
Oral vancomycin
Fidaxomicin (new and expensive)
Stool transplants
Surgery may be required
How do we manage C Diff infection?
Reduce prescription of broad spectrum antibiotics
Avoid 4 C’s
Antimicrobial management team
Isolate symptomatic patients
Wash hands between patients
What is management of Cdiff?
- Stop precipitating antibiotic (if possible)
- Follow published treatment algorithm – oral metronidazole if no severity markers
- Oral vancomycin if 2 or more severity markers
What parasites are responsible for diarrhoea?
Protozoa and helminths
Diagnosis generally by microscopy
•Send stool with request “parasites, cysts and ova please” or P, C and O
UK parasites include Giardia lamblia (metrodonidazole) and cryptosporidium parvum (no treatment) - these are both from contaminated water
Which imported parasite is responsible for amoebic dysentery?
Entamoeba histolytica
Amoebic liver abscess may be long term complication (anchovy pus)
Treat with metrodonidazole
Which viruses can cause diarrhoea?
- Potentially many causes including adenovirus
- rotavirus in children under 5 yrs
- common in winter
Noroviruses - common cause of outbreaks - diagnosis by PCR, very infectious
How is diagnosis of vral diarhoea made?
Antigen detection
