Enteric Infections Flashcards
(44 cards)
1
Q
Gastrointestinal Natural Resistance to Infection
A
- We routinely cope with low-level bacterial infection in food due to natural defenses in GI tract
- Gastric acid - fat in diet may protect pathogens in transit
- Bile salts - in duodenum disrupt some cell surfaces
- Normal commensal flora
- Modify environment with metabolites
- Compete for nutrients
- Produce natural antibiotics
- Mucosal immunity
- Cell-mediated immunity
- Secretory IgA (also in breast milk)
- Motility - diarrhoea probably important in clearing pathogens
2
Q
Hydration/Rehydration
A
- Our survival depends upon the fluid absorption capacity of the gut
- Adult gut handles 6,500 ml of fluid/day
- Food
- Saliva
- Gastric/pancreatic/biliary fluids
- Volume reduced to 1,500ml by distal ileum
- Reduced further in colon –> stool egestion of <250ml a day
- Adult gut handles 6,500 ml of fluid/day
- Diarrhoea due to:
- Secretory (chloride or calcium mediated)
- +/- Osmotic (damage to villous brush border)
- Oral rehydration therapy - oral rehydration salts (ORS)
- Rely on coupled transport of sodium and glucose into enterocytes so that water follows osmotic gradient
- Now a standard of care
3
Q
Types of Enteric Infection
A
- Type 1: Non-inflammatory (watery diarrhoea) e.g.
- Toxin-mediated
- C.perfringens
- B.cereus
- S.aureus
- Giardia
- Cryptosporidium
- Rotavirus
- Norovirus
- ETEC
- EPEC
- Toxin-mediated
-
Type 2: Inflammatory (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
4
Q
Standard Management
A
- Often uncomplicated and self-limiting
- Mainstay of treatment is supportive
- Rehydration therapy
- Little role for anti-diarrhoheal agents
- Some bacteria or parasites may require specific antimicrobial therapy
- Assessing dehydraion correctly and early important
- Infants more susceptible as:
- Higher body surface to volume ration
- Smaller fluid reservoir
- Dependent on other for fluid intake
- Signs of severe dehydration
- Apathy
- Tachycardia (bradycardia if extreme)
- Weak pulse
- Deep breathing
- Deep dunken eyes
- No tears
- Parched mouth
- Skin recoil >2 seconds
- Minimal urine output
- Infants more susceptible as:
5
Q
Basic Diagnosis (Bacteria/Parasites)
A
- Rarely possible on clinical features alone
- Epidemiology - as part of an outbreak
- Microbial investigation
- Rarely necessary unless:
- Dehydrated
- Febrile
- Blood or pus in stool
- Part of outbreak
- Stool +/- blood culture
- Sekective indicator growth mediator
- Diagnostic yield of stool culture approximately 5%
- Microsopy of stool for:
- Ova
- Cysts
- Parasites
- Specific typing
- Rarely necessary unless:
6
Q
E.Coli
A
- Major part of normal gut flora
- Until recently role uncertain as difficult to distinguish pathogens from commensals
- Enterotoxic E.coli (ETEC)
- Produces two main types of polypeptide toxins (similar to cholera) –> hypersecretion of fluid into lumen
- Verycytotoxic (VTEC) or Enterohaemorrhagic (EHEC)
- Produces cell killing cytotoxin (similar to shigella)
- Can ==>
- Haemmorhagic colitis
- Haemolytic uraemic syndrome (HUS)
- Enteroinvasive (EIEC)
- Enteropathogenic (EPEC)
- Enterotoxic E.coli (ETEC)
7
Q
E.Coli - Epidemiology
A
- Transmission by:
- Faecal-oral
- Direct
- Food or water
- ETEC
- Commonest cause of bacterial diarrhoea in children in areas of poor hygeine
- Uncommon in Western Europe
- Important cause of travellers’ diarrhoea
- Reservoir = human GI tract
- VTEC
- Several types - commonest is 0157
- Now a common cause of acute renal failure in Western countries
- Reservoir = GI tract of healthy cattle
- Transmission by:
- Contaminated food/animal carcases (e.g. hamburgers)
- Unpasteurised milk
- Farms
- Paddling pools
- Rarely person to person e.g. nurseries
- Several types - commonest is 0157
8
Q
E.Coli - Clinical Features
A
- Incubation period usueally 1-5 days (can be up to 14)
- Abrupt onset vomiting and diarrhoea
- ==> later profuse watery diarrhoea only
- Mild fever
- Little pain
- Similar presentation to viral gastroenteritis/salmonellosis
9
Q
E.Coli - Haemorrhagic Colitis
A
- Possible complication of 0157 infection in children and adults
- Typically diarrhoea escalates to bloody with abdominal pain
- Fever usually low
- May be mistaken for acute inflammatory bowel disease
10
Q
E.Coli - Haemolytic Uraemic Syndrome
A
- May accompany colitis as a complication of infection
- Affects 10% of children in outbreaks
- Characterised by:
- Rising urea and creatinine (AKI)
- Haemolytic anaemia
- Thrombocytopenia
- Raised BP
- Prognosis
- >50% need haemodialysis
- Only fatal in <5% - mostly elderly
- Preceeding GI illness may go unrecognised
- Shiga-toxin binds to glomerular epithelium ==> apoptosis + bind leukocytes + become thrombogenic ==> activated platelet complexes lodge in capillaries and arterioles ==> destruction of RBCs (microangiopathic haemolysis)
11
Q
E.Coli - Laboratory diagnosis
A
- Difficult as pathogen and normal flora are the same species
- 0157:
- Phage typing
- Doesn’t ferment sorbitol
- Immunological cytotoxin detection
- PCR detection of cytotoxin gene
12
Q
E.Coli - Management
A
- Mostly supportive
- Many E.Coli are resistant to broad spectrum antibiotics e.e.g penicillins, cephalosporins, trimethoprim
- Rx -* ciprofloxacin* 500mg BD for 3-5 days
- **! **- Avoid antibiotics in HUS as bactericidal ==> toxin release
- Antimotility drugs probably increase chance of HUS through delayed clearance of toxin
13
Q
Salmonella
A
- Common cause of food poisoning
- Infects humans and other animals
- >2000 serotypes
- Commonest are S.enteritidis, S.typhimurium and S.virchow
-
Cause of typhoid and paratyphoid fevers
- These are exclusive human pathogens
14
Q
Salmonella - Food Poisoning
A
- Contaminated poultry/dairy products common source
- Not usually from food handlers or person to person spread
- Reservoir - GI tract of birds, reptiles, amphibians
- Commoner in summer/hot weather
- Microbiology:
- Identified on specific media by biochemical features:
- Non-lactose fermenters
- Produce H2S
- LPS is O antigen, flagellae H antigen - defines serotypes
- Identified on specific media by biochemical features:
15
Q
Salmonella - Food Poisoning - Pathogenesis
A
- Infection of gut epithelium
- Does not extend beyond basement membrane
- ==> Excess fluid secretion from ileum/jejenum
- If transported through cells ==> systemic infection
- Survives in macrophages
16
Q
Salmonella - Food Poisoning - Clincal Features
A
- Incubation period 12-72 hours
- Symptoms:
- Malaise
- Nausea
- Vomiting
- Fever
- ==> Watery-brown diarrhoea follows rapidly
- Abdominal pain common but not severe
- Often resolves in several days, some cases last several weeks
- Children and elderly at risk of hypovolaemia
17
Q
Salmonella - Food Poisoning - Complications
A
- Salmonella colitis
- Affects up to 10% ==> colic and bloody stools
- Bacteraemia
- ==> Seeding to bones/joints in sickle cell disease patients
- ==> Aneurysms
- Post-infectious reactive arthritis
- Prolonged excretion in:
- Diverticulosis
- IBD
- HIV
18
Q
Salmonella - Microbiology
A
- Stool culture
- Blood culture if high fever or very unwell
- Selective agar to inhibit normal flora + indicator
- Indicator often lactose red ==> pink colonies due to lactose fermentation and acid production
- Typing:
- Bacteriophage
- Antibiotic panels
19
Q
Salmonella - Food Poisoning - Management
A
- Rehydration
- Antibiotics if:
- No recovery after 48 hours
- Shock
- High risk
- Valve disease
- Prosthesis
- *Ciprofloxacin *first line (alternative is cefotaxime)
20
Q
Shigellosis (Bacillary Dysentery) - Epidemiology
A
- Worldwide problem
- In Western countries endemic Shigellae usually cause mild illness
- Few thousand cases a year in the UK
- Tropical strains tend to be more severe and persistent
- Transmission via
- Person to person spread
- Contaminated food and water
- Reservoir = human GI tract
21
Q
Shigellosis - Pathogenesis
A
- Few thousand cases a year in the UK
- Suptypes:
- *S.sonnei - *most common
- S.flexneri
- S.boydii
- *S.dysenteriae - *type 1 produces shiga exotoxin
- Invade gut by:
- Destroying submucosa
- Infecting enterocytes
- Spread for cell to cell
22
Q
Shigellosis - Clinical Features
A
- Incubation period of 1-7 days
- Course:
- High fever
- High WBC
- With resolving fever ==> diarrhoea and colic
- S.sonnei and *S.boydii *are mild - rarely cause colitis
- *S.flexneri * and S.dysenteriae are more severe ==> mucus and blood in stool + marked colic
- Asymptomatic excretion for days-weeks
23
Q
Shigellosis - Microbiology
A
- Like E.coli
- Non-lactose fermentors
- Non-motiles
- Serotype on basis of O antigens
24
Q
Shigellosis - Management
A
- Symptomatic
- Antispasmodics
- Rehydrate
- Abx in severe cases
- Rx- *ciprofloxacin (trimethoprim/ceftriaxone *alternatively)
25
Campylobacter
* Commonest cause of food poisoning
* \>50,000 cases per year in the UK
* Mostly sporadic - undercooked poultry, bird pecked milk
* Large food/waterborne outbreaks can occur
* Incidence higher in summer
* Person to person spread uncommon
* Animal pathogen - several species can infect humans:
* *C.jejuni*
* *C.coli*
* *C.fetus*
* *C.lari*
26
Campylobacter Jejuni
* Low infective dose
* Cell-wall LPS
* Produces enterotoxin and cytotoxin
27
Campylobacter - Clinical Features
* Incubation period 2-5 days (up to 9)
* 24 hour prodrome - fever + headache
* Symptoms:
* Watery diarrhoea - can be bloody
* Vomiting
* Significant pain - constant not colicky
* Pain with little diarrhoea can occur - similar to acute abdomen presentation
* Systemic infection rare
* Commonest antecedent infection identified in Guillain Barré Syndrome (a post-infectious peripheral neuropathy)
28
Campylobacter - Microbiology
* Selective media with antibiotics
* 43ºC incubation may improve selection
* Microaerophilic
* Gull wing morphology
29
Campylobacter - Management
* Mild cases usually self-limiting
* Severe/prolonged cases - Rx 3-4 day course of oral *erythromycin*
* *Ciprofloxacin *active against
30
Clostridium Difficile
* Commonest cause of hospital-acquired diarrhoea
* Gut commensal in 3% of healthy adults and 66% of children
* Some antibiotics disturb normal balance of microbial flora ==\> rapid multiplication of *C.difficile* ==\> toxin production ==\> mucosal injury and inflammation ==\> diarrhoea
31
Clostridium Difficile - Clincal Presentation
32
Clostridium Difficile - Risk Groups
* Age \>65 years
* Antibiotic treatment - especially:
* *Clindamycin*
* *Cephalosporins*
* *Penicillins*
* **GI surgery/manipulation
* Long stay in hospital/residential care
* Immunosuppression
33
Clostridium Difficile - Managment
* Confirm diagnosis by *C.difficile* toxin testing
* Stop or change antibiotics if possible
* Fluid/electrolyte replacement
* Avoid antiperistaltics
* If above not possible or unseuccessful - Rx *metronidazole*
* *vancomycin * second line
* Infection control
34
Viral Gastroenteritis
* Common pathogens:
* *Rotavirus*
* *Adenovirus*
* *Norovirus*
* *Astrovirus*
* Commonest cause of symptomatic intestinal infection in Western world
* Rarely severe or fatal in UK
* Significant cause of infant mortality in resource poor countries
35
Viral Gastroenteritis - Management
* All self-limiting in the normal host
* Rehydration is the key
* Prevention of spread
* Faecal-oral, person-person, food
* Antiviral therapy not used/available
36
Viral Gastroenteritis - Diagnosis
* Rarely possible on clinical grounds
* Epidemiology
* Stool electron microscopy - ‘catch all’
* Stool enzyme immunoassays (e.g. rotavirus)
* Molecular diagnosis
* Stool PCR
* Outbreak typing and molecular epidemiology
* None of these viruses can be grown in cell culture
37
Rotavirus
* Commonest cause of viral gastroenteritis in young children
* 1 million deaths/yr worldwide
* \>10,000 cases/yr UK - under-reported
* Peak incidence 6-24 months, uncommon \>5yrs but adult infection occurs and can be symptomatic – may cause outbreaks in elderly care homes
* Seasonal, late winter
38
Rotavirus - Virology
* Reovirus
* Segmented dsRNA genome
* No envelope
* Seven serogroups (A-G)
* Gp A human, others infect different animals e.g. pigs
* Genomes can reassort (like flu A) ==\> possibility of new human strains
* Reservoir GI tract humans
* 1 billion viruses/ml faeces - only 10 needed for infection
39
Rotavirus - Clinical Features
* Incubation around 1 day
* Abrupt onset diarrohea and vomiting (D\>V)
* Mild fever - short-lived
* Recovery in 48 hrs usual (diarrhoea for up to a week)
* Blood in stool can occur-investigate further
* Gross dehydration and shock
* Adults may have mild disease, transient vomiting
* Persistent diarrhoea may occur in immunosuppressed
40
Rotavirus Vaccine
* Original tetravalent rhesus monkey/human reassortment vaccine (Rotashield) withdrawn over concerns regarding intussusception
* New live attenuated vaccines (Rotarix and RotaTeq) highly effective against severe disease
* Protection against severe disease, not necessarily against infection
* Rotarix added to UK Childhood immunization programme in 2013 – 2 doses given at 2 months and 3 months of age
41
Calciviruses
* Types:
* *Norovirus*
* *Sapovirus (SRSV)*
* + ssRNA, non-enveloped, does not grow in routine cell culture
* Reservoir human GI tract
* May be concentrated in bivalve molluscs
42
Norovirus Gastroenteritis
* Incubation 10-50 hrs
* Asymptomatic to explosive vomiting and diarrhoea
* Headache and abdominal cramps
* Lasts 24-48 hrs
* Common defined outbreak cause (50-60%)
* Closed communities/hospitals/cruise ships
* Breathe in aerosolised vomit/faeces and swallow
* Infectious dose low
43
Enteric Adenoviruses
* Second most common cause of infantile diarrhoea in temperate climates
* Adenoviruses cause many diseases
* Non-enveloped, dsDNA
* Virology
* Subgroups A-F - gastroenteritis agents are group F: types 40/41
* Poor growth in cell culture
* Standard clinical picture:
* Incubation period up to 10 days ==\>
* Watery diarrhoea
* Mild fever
* Illness may last longer but in general (3-11 days)
44
Astroviruses
* Infants and elderly exhibit significant illness
* Severity lower than other agents
* Often co-infection with *rotavirus/norovirus*
* \<5% hospitalised cases viral gastroenteritis
* Commoner in winter time
* Virology
* +ssRNA
* Non-enveloped
* 5-6 pointed star
* Several serotypes
