Microbiology Enteric Infections Flashcards
Common
- Campylobacter ep.,
- Salmonella sp. (food poisoning)
- Shigella sp,.
- E.Coli
Less common
- Paratyphi (enteric fevers)
- Virbio parahaemolyticus
- Vibrio cholera
- C.Diff
- C. perfringens
- Listeri
- Helicobacter pylori
- Aeromonas sp.,
- Plesiomonas sp.
Performed Toxins
- Staphylococcis aureus
- Bacillus cereus (rice)
- Clostridium botuinum
- Perfringens
Common Gastroenteritis Viruses:
- Rotavirus (most common)
- Calciciviruses (Norovirus, Sapovirus)
- Adenoviruses
- Astrovirusus
- (Hepatitis A and E)
- Many others found in GI tract as part of systemic infection
Parasites
Protoazoa:
• Giardia intestinals
• Cryptosporidium parvum
• Entamoeba histolytica
Helminths
• Ascaris lumbricoides
• Hookworms
• Tapeworms
Acute gastroenteritis in USA
> 30 million episodes/yr
1.5 million OPD visits/yr
200,000 hospitalisations/yr
Around 300 deaths/yr
Developing Countries diarrhoea
Is a common cause of death in under 5’s – 2 million deaths per year
Oral Rehydration Therapy
Diarrhoea secretory (Chloride or calcium mediated) +/- osmotic (damage to villous brush border) Success of ORS relies on coupled transport of sodium and glucose into enterocytes so that water follows the gradient.
Common Presenting Features
Diarrhoea (uncomplicated or collities) – D & V may be first stages of UTI, meningitis Vomiting Fever Recent contact environmental link Epidemiology
Types of enteric infection
Type 1: Non-inflammatory (Watery diarrhoea) e.g. toxin mediated (c. perfringens, B. cerues, S. aureus), Giardia, Cryptosporidium, Rotavirus, Norovirus, ETEC, EPEC
Type 2: Inflammtory (dysentery, faecal leukocytes, lactoferrin) e.g. Shigella, VTEC, C. difficile, C. jejuni, S.enteritidus, Entamoeba.
Type 3: Penetrating (Enteric Fever) e.g. S. Typhi, yersinia
Standard Management
Often uncomplicated an self-limiting Mainstay of treatment is supportive • Rehydration • Little role for anti-diarrhoeal agents Specific: therapy may be required • Some bacteria and some parasites require antimicrobial therapy
Assessment of Dehydration
Correct, early assessment essential
Infants more prone as higher body surface to volume ratio, smaller fluid reservoir, dependent on others for fluids
Signs
Signs of severe dehydration
Apathy, tachycardia (bradycardia if extreme), weak pulse, deep breathing, deep sunken eyes, no tears, parched mouth, skin recoil >2 secs, minimal urine output.
Basic Diagnosis
Rarely possible on clinical features alone
Epidemiology (e.g. par of outbreak)
Microbiological investigation
• Rarely necessary unless dehydration, febrile, blood or pus in stool, or part of outbreak
• Stoll +/- blood culture, selective, indicator growth media (diagnostic yield Stool culture – 5%)
• Microscopy of stool for ova, cysts, parasites
• Specific typing
Prevention
Avoidance of risk • Don’t travel? • Basic Hygiene, hand washing • Clean water, clean food, adequate cooking • Immunisation (Typhoid, rotavirus) • Hospital infection control
E.Coli
Description
- E.coli is a major part of normal gut flora.
* Until recently role uncertain as difficult to distinguish pathogens from commensals
Pathogenic forms of E.Coli
- Enterotoxigenic E. Coli (ETEC)
- Verocytotoxic (VTEC) or Enterohaemorrhagic (EHEC)
- Enterinasive (EIEC)
- Enteropathogenic (EPEC)
Pathogenicity of ETEC
Produce 2 main types of toxin
• Polypeptide, like cholera toxin
• Stimulates hypersecretion
Pathogenicity of VTEC
Or Haemmohagic
• Cytotoxin, Kills cells, like Shigella toxin
• Haemorrhagic colitis and HUS (Haemolytic uremic syndrome)
Spread ecoli
All Faecal-oral, direct, food or water
ETEC epidemiology
Commonest cause bacterial diarrhoea in children in areas of poor hygiene, uncommon W Europe, important cause traveller’s diarrhoea.
Reservoir-human GI tract
VTEC Epidemiology
Several types, commonest O157, now common cause of acute renal failure in Western countries.
Reservoir-GI tract of healthy cattle
Contaminated food/animal carcasses (hamburgers0, unpasteurised milk, farms, paddling pools person to person rare e.g. nurseries
E.Coli Clinical Features (general)
Incubation usually 1-5 days (up to 14)
Abrupt onset vomiting and diarrhoea – later profuse watery diarrhoea only
Mild fever, little pain
Similar to viral gastroenteritis/salmonellosis (early stage but complications)
E.Coli
Severe complications
Haemorrhagic Colitis
Haemolytic Uraemic Syndrome
E.Coli
Haemorrhagic Colitis
- May complicated O157 infection in children and adults 699 positive stool cultures in 2004
- Typical diarrhoea progressing to bloody with abdominal pain
- Fever usually low
- May be mistaken for acute inflammatory bowel disease (as the preceding infection not severe)
E.Coli
Haemolytic Uraemia Syndrome
- May accompany colitis as a complication – 10% children in outbreaks
- Rising urea and creatinine, haemolytic anaemia and thrombocytopaenia
- Raising BP, fitting
- More than half need haemodialysis, almost all caes recover (most deaths in elderly, fatal <5%)
- Preceding GI illness may be unrecognised
- Mucosal damage and microangiopathic haemolytic anaemia and renal vascular disease
E.Coli
Laboratory Diagnosis
- Difficult – pathogen and normal flora are same species
- O157 phage typing
- O157 doesn’t ferment sorbitol
- Immunological cytotoxin detection
- PCR detection of cytotoxin gene
E.Coli
Management
- Supportive
- Many E.coli resistant to broad spectrum penicillins, cephalosporins, trimethoprim
- Ciprofloxacin 500 mg BD, 3-5 days
- Avoid antibiotics in HUS
- Anti-motility drugs probably increase change of HUS through delayed clearance of toxin
