Micro: GI Infections Flashcards
Epidemiology of GI infections
- Vulnerable groups: infants and elderly
- Most are self-limiting (hence do not seek medical care)
Reportable GI infections
Most gastroenteritis cases are reportable. However these are the most important to report:
* Camplybacter
* Salmonella
* Shigella
* Escherichia coli O157
* Listeria
3 types of clinical syndromes associated with GI infections
Secretory diarrhoea
Inflammatory diarrhoea
Enteric fever
How can you differentiate between the different GI infections clinical syndromes
If main symptoms are gastroenteritis (diarrhoea, GI cramps) then check if they have a a fever:
- no fever = secretory diarrhoea
- fever = inflammatory diarrhoea
If main symptom is fever and systemically unwell with fewer GI side effects = enteric fever
Secretory diarrhoea:
- Pathophysiology
- Main symptoms
- Common causative pathogens
Pathophysiology
- Toxin production can either 1) induce cAMP in enterocytes which opens Cl- channels at apical membrane of enterocytes causing a Cl- efflux into lumen which results in watery diarrhoea and dehydration OR 2) toxin superantigen binds to T cell receptors causing massice cytokine release which causes Cl- secreted into lumen.
Symptoms
- Watery diarrhoea with NO fever
- no inflammatory cells in stool
Common causative pathogens
- Cholera
- Enterobacteriacae (ETEC, EPEC)
- Viruses (Norovirus, Adenovirus, Rotavirus)
Inflammatory diarrhoea:
- Pathophysiology
- Main symptoms
- Common causative pathogens
Pathophysiology
- inflammation AND bacteraemia which in immunocompromised patients may result in shock
Symptoms
- Bloody diarrhoea (=dysentery) with inflammatory cells in stool
- Fever
Common causative pathogens
(CHESS)
- Campylobacter
- EHEC
- Entamoeba
- Salmonella (non-typhoidal)
- Shigella
Enteric diarrhoea:
- Main symptoms
- Common causative pathogens
Main Symptoms
- Systemically unwell
- Fever
- Fewer GI symptoms
Common Causative Pathogens
- Typhoidal salmonella
- Yersinia
- Brucella
these are more severe GI infections
What type of organism is Staph. Aureus (4)
Gram positive cocci appearing in clusters
Catalase and coagulase positive
Aerobic
Yellow in agar plate
GI infection: Staph. Aureus
How does Staph. Aureus cause a GI infection
Produces enterotoxin which acts as a superantigen causing IL1/2 release
GI infection: Staph. Aureus
Incubation & Duration
How is it spread
- VERY SHORT incubation of 2-4 hours
- Duration of <1 day
- Spread by skin lesions (commonly through infected food handlers)
GI infection: Staph. Aureus
Symptoms and Treatment
Symptoms
Prominent vomiting
Watery non-bloody diarrhoea
type of secretory diarrhoea
Treatment
Self-limiting
What type of organism is Bacilus Cereus (3)
Gram positive rods
Aerobe
Spore forming
GI infection: B. Cereus
Source of infection
Incubation & Duration period
Source of infection
- Reheated rice (reheating causes to germinate)
Incubation & Duration
Incubation = 1-6 hours
Duration = <1 day
GI infection: B. Cereus
Pathophysiology
Symptoms (and complications)
Treatment
Pathophysiology
- Produces toxins. Heat-stable emetic toxin (not destroyed upon reheating) and heat-labile diarrhoeal toxin(destroyed in reheating, but present in improper heating of food)
Symptoms
Vomiting and non-bloody watery diarrhoea
May cause bacteraemia and cerebral abscesses in vulnerable populations
Treatment
Self-limiting
What type of organism is Clostridium
What are the different types of Clostridium
Gram positive rod + anaerobe
Types
- Clostridium Botulinum
- Clostridium Perfringens
- Clostridium Difficile
GI infections: Clostridium
Differentiate between the different types of Clostridium infections
Clostridium botulinum - causes botulism
- From canned food and packed food (honey, beans)
- Causes disease due to preformed toxin which cleaves SNARE proteins preventing acetylcholine release at peripheral nerve synapses resulting in descending paralysis (differentiate from GBS - ascending)
- Treated with antitoxin
Clostridium perfringens - food poisoning
- From reheated food (8-16hr incubation)
- Generates a superantigen that mainly affects the colon
- Causes watery diarrhoea and cramps that last 24 hours
- Complication: gas gangrene
Clostridium difficile - pseudomembranous colitis
- Hospital-acquired infection related to antibiotic use (4C’s: cephalosproins, Ciprofloxacin, Clindamycin, Co-Amoxiclav)
- Has 2 exotoxins (A, B)
- Treatment: 1) stop offending abx 1) Vancomycin (second line=fidaxomicin)
What type of organism is Listeria (3)
Gram positive rod
Beta-haemolytic, aesculin-positive
Motile
GI infection: Listeria Monocytogenes
Source of infection
Refrigerated food (sandwich, veggies)
Unpasteurised dairy (monocyto-cheese!)
Often causing an outbreak of febrile gastroenteritis
GI infection: Listeria Monocytogenes
Symptoms
Treatment
Symptoms
- Fever + watery diarrhoea
- Headache
- Little vomiting
- most vulnerable groups = perinatal infection (may result in stillbirth) and immunocompromised pts
Treatment
- Ampicillin
What are the gram positive bacteria which may cause a GI infection
Staph A (cocci + clusters)
Bacillus Cereus (rods + aerobic + spore forming)
Clostridium (rods + anaerobic)
Listeria (rods + beta haemolytic + motile)
What type of organisms are Enterobacteriaceae (4)
- Gram negative
- Faculative anaerobe (makes ATP if O2 present but can undergo fermentation in anaerobic environments)
- Lactose fermenters
- Oxidase-negatieve
GI infection: E.Coli
Differentiate between the different types of infection
ETEC
- Toxigenic
- Main cause of travellers’ diarrhoea
EPEC
- Pathogenic
- Infantile diarrhoea
EIEC
- Invasive
- Dysentry
EHEC
- Haemorrhagic
- Caused by E. coli 0157:H7
- May result in haemolytic uraemic syndrome (due to shiga-like vierocytotoxin)
- Dysentery + MAHA + Renal failure
- Incubation of 1-5 days and duration 1-4 days
NOTE: ALL are spread through faecal-oral route
GI infection: E.Coli
Treatment
Self-limiting
Avoid abx - thought to exacerbate condition
What type of organisms are Salmonella (4)
- Gram negatives
- Non-lactose fermenting
- Produce hydrogen sulphide (forming black colonies)
- Motile
How can you differentiate the different types of Salmonellae?
Difference in antigens found on bacterium
- Cell wall O (groups A-I)
- Flagellar H
- Capular Vi (virulence, antiphagocytic)
List two species of Salmonella.
- Salmonella typhi (and paratyphi)
- Salmonella enteritidis
GI infection: Salmonella Enteritidis and Typhi
Differentiate between the two types of Salmonella infection
Salmonella Enteritidis
- invasion of epi and sub epithelial tissue of small and large bowel causing entercolitis
- non-bloody diarrhoea (stool +ve cultures)
- 12-48hr incubation period
- No fever and bacteriaemia is rare
- Transmitted by poultry, eggs, meat, reptile pets
Salmonella Typhi
- Transmitted only by humans
- Multiples in Peyer’s patches and spreads via endoretircular system (resulting in bacteraemia - +ve blood cultures)
- Sx = Slow onset fever and constipation + splenomegaly + rose spots + anaemia + leucopaenia (fever in returning traveller!)
GI infection: Salmonella Enteritidis and Typhi
Treatment
Salmonella Enteritidis = self-limiting
Salmonella typhi = IV ceftriaxone then PO azithromycin
What type of organism is Shigella (4)
- Gram negative
- Non-lactose fermenter
- Does NOT produce hydrogen suphide
- Non-motile
GI infection: Shigella
Pathophysiology
- Produces shiga toxin affecting teh distal ileum and colon resulting in mucosal inflammation
- Highly infectious (very small infective dose - lowest of GI infections!!!) hence behind many outbreaks
Incubation of 12-96 hours with Duration of 5-7 days
GI infection: Shigella
Symptoms
Treatment
Symptoms
- Dysentery (severe diarrhoea with blood and mucus)
- Fever
- Abdominal pain
Treatment
- Self-limiting
- Try to avoid abx but Ciprofloxacin can be given if needed
What type of organism is Vibrio
Gram negative
Comma-shaped
Late lactose-fermenters
Oxidase-positive
GI infection: Vibrio Cholera
Pathophysiology
Colonisation of small bowel, where enterotoxin stimulates cAMP resulting in opening of Cl- channels and Cl- efflux out of cells. This results in Na+ moving out and water following by osmosis ==> severe dehydration!
Transmitted by human faeces in contaminated water (especially in water borne food - rice, shellfish)
GI infection: Vibrio Cholera
Symptoms and treatment
Symptoms
Rice water stool - watery diarrhoea without inflammatory cells
Treatment
Self-limiting
GI infection: Vibrio
Outliune the key features of other types of vibirio (excluding cholera)
Vibrio parahaemolyticus:
- Caused by ingestion of raw/undercooked seafood
- Causes self-limiting diarrhoea
- Grows on salty agar
Vibrio vulnificus:
- Causes cellulitis in shellfish handlers
- Can cause fatal septicaemia with D&V in HIV patients, treated with doxycycline
Both self-limiting
What type of organism is Campylobacter
- Gram negative s-shaped rod
- Oxidase-positive
- Grows at 42 degrees C
- Motile
GI infections: Campylobacter
Spread
Symptoms
Spread
Undercooked Poultry
BBQ!!!!
Symptoms
* Prodrome of fever and headahce
* Followed by abdominal cramps
* Bloody diarrhoea
* Lasts for 2-20 days
GI infections: Campylobacter
Treatment
Complications
Treatment
- Erithromycin or Cirpo if in first 5 days
- Otherwise after self-limiting - only treat if immunocompromised
Complications
- GBS
- Reactive arthritis
GI infections: Yersinia Enterocolitica
Key features
Sources: undercooked pork
Symptoms
- Fever, abdo pain, diarrhoea
- (presentation may be like appendicitis)
- Associated with reactive arthritis
What gram negative bacteria can cause GI infections
- Enterobacteriaceae (lactose fermenters, oxidase negative)
- Salmonella (non-lactose, H2S producers, motile)
- Shigella (non-lactose, non-H2S, non-motile)
- Vibrio (comma-shaped, late lactose, oxidase positive)
- Campylobacter (s-shaped/comma, lactose, oxidase, 42C, motile)
- Yersinia E.
Protozoa which may cause GI infections & Key features
Entamoeba Histolytica
- Flask-shaped ulcer in colon (seen on histology)
- Sx: dystentery + flatulence + tenesmus
- common in MSM
- Dx: stool micro and serology
- Complications: chronic infection may lead to liver abscess (RUQ pain, weightloss, fevers)
- Rx: Metronidazole + Dantomyocin
Giardia Lamblia
- commonest protozoa GI infection
- Pear-shaped trophozoite with 2 nuclei and 4 flagellae
- Risk factors: travellers from South-East Asia
- Spread from contaminated water + food
- Sx: foul-smelling non-blood diarrhoea (as causes malabsorption of fat and protein) + lots of cramps + NO fevers
- Dx: stool micro + ELISA
- Rx: Metronidazole
Differentiate between viruses which may cause GI infections & Key features
Norovirus
- GII.4 is the commonest strain
- Adult outbreak of secretory diarrhoea (has low infectious dose)
Adenovirus
- Secretory diarrhoea in <2yo or Immunosuppressed
Rotavirus
- dsDNA affecting mucosa of small intestine
- Nursery outbreaks (<6yo)
- most children by age of 6 will have abs to at least 2 type - recurrent infection eventually leads to life long immunity
Prevention measures against GI infections
- Handwashing!!!!!!
- Food washing
- Vaccination
Which causes of GI infections have available vaccines
- Cholera (serogroup O1)
- Campylobacter
- ETEC
- Salmonella typhi
- Rotavirus (rotarix (live, monovalent), rotateq (pentavalent), rotashield (used if risk of intussusception))
