GI Infections Flashcards

Question 1

Q

Define Gastroenteritis

Answer

A

Rapid onset diarrhoeal illness, lasting <2 weeks with diarrhoea (loose or unformed stool) ≥3/day or ≥200g of stool which is either viral or bacterial in aetiology

Question 2

Q

Define diarrhoea.

Answer

A

loose or watery stool, ≥3 times in 24 hours, acute/chronic/persistent

Question 3

Q

What is the difference between acute, persistent and chronic diarrhoea?

Answer

A

Acute <14 days (may be viral or bacterial)
Persistent 14-29 days
Chronic >30 days (may be due to parasites and non-infectious aetiology)

Question 4

Q

What is small and large bowel diarrhoea?

Answer

A

Small bowel diarrhoea = watery, crampy abdominal pain, bloating and gas; inflammatory cells rare
Large bowel diarrhoea = small volume, painful, occur with blood/mucous; inflammatory cells common

Question 5

Q

What are the RFs for gastroenteritis?

Answer

A

Food borne
Exposure-related
Host-related

Question 6

Q

What are the exposure-related RFs for gastroenteritis?

Answer

A

Outbreak situation (>2 cases of common food source or exposure)
Travel history (exposure to poor settings and water facilities)
Occupational exposure / Health-care related exposure (recent ABx  c. diff)
Animal contacts (pets, farms, zoos)
Reptile contact (specifically)
Institution/childcare facility

Question 7

Q

What are the host-related RFs for gastroenteritis?

Answer

A

Young children and elderly
Immunosuppressed patients
MSM (men who have sex with men)
Anal-genital, oral-anal, or digital-anal contact
Haemochromatosis or haemoglobinopathy

Question 8

Q

Describe the epidemiology of GI infections.

Answer

A

There is an underreporting of GI infections (most are self-limiting <24 hours, patients do not seek healthcare)
Viral (i.e. norovirus) >>> bacterial
Developing countries have outbreaks (especially cholera in war torn countries)

Question 9

Q

What is the mechanism of disease?

Answer

A

(1) Secretory diarrhoea (from toxin production):
- Cholera toxin:
  - Subunit production
  - cAMP opens Cl^- channels at the apical membrane of the enterocytes causing an efflux of Cl^- to lumen with loss of water and electrolytes → profoundly dehydrated
- Superantigens:
  - Superantigens bind directly to TCRs and MHC molecules; outside the peptide binding site: there is massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response) → secretory diarrhoea
(2) Inflammatory diarrhoea
(3) Enteric fever – host responses in bacteraemia are…
- Inflammatory (exudative) diarrhoea
- Enteric fever: interstitial inflammation

Question 10

Q

How do we diagnose GI infections?

Question 11

Q

What are the extra-intestinal manifestations of GI infections? What are the causative organisms?

Answer

A

Salmonella, Yersinia → aortitis, osteomyelitis, deep tissue infection
Campylobacter, Yersinia → haemolytic anaemia
Shigella, Campylobacter, Yersinia → Glomerulonephritis
STEC, Shigella → HUS
Yersinia, Campylobacter, Salmonella, Shigella → erythema nodosum
Salmonella, Shigella, Campylobacter, yersinia, (giardia, Cyclospora cayetanensis) → reactive arthritis
Listeria, salmonella (infants <3m) (also enteroviruses) → meningitis

Question 12

Q

Describe staphylococcus aureus?

Answer

A

1/3 population chronic carriers, 1/3 transient
Spread by skin lesions on food handlers
Appears in tetrads, clusters on gram stain → yellow colonies on blood agar
SUPERANTIGEN: produces enterotoxin, an exotoxin that can act as a superantigen in the GI tract, releasing IL1 and IL2 causing prominent vomiting and watery, non-bloody diarrhoea
Mx: self-limiting

Question 13

Q

What are the gram +ve rods: spore forming bacteria?

Answer

A

Bacillus cereus

Clostridia

Listeria monocytogenes:

Question 14

Q

Describe bacillus cereus.

Answer

A

Gram-positive rods: spore forming
Bacillus cereus: food poisoning
- Spores germinate in reheated fried rice (heat-stable emetic toxin – not destroyed by reheating)
- Gram +ve rod-spores
- Heat-labile diarrhoeal toxin (food is not cooked to a high enough temperature)
- Watery non-bloody diarrhoea; self-limiting
- Rare cause of bacteraemia in vulnerable population
- Can cause cerebral abscesses

Question 15

Q

What are the types of clostridia? What is the source? What do you ingest? What does it do? How do we treat it?

Answer

A

Clostridia (gram +ve anaerobe)
- Clostridium botulinum: botulism
  - Source: canned or vacuum-packed food (honey in infants)
  - Ingestion of preformed toxin (inactivated by cooking)
  - Blocks ACh release from peripheral nerve synapses: paralysis
  - Treatment with antitoxin
  - Clostridium pefringens: food poisoning
    - Source: reheated food (meat)
    - Normal flora of colon but not small bowel, where the enterotoxin acts (superantigen)
    - Incubation is 8-16hrs
    - Watery diarrhoea, cramps, vomiting lasting 24hrs
  - Clostridium difficile: pseudomembranous colitis
    - Produces 2 toxins – Toxin A and Toxin B
      - Toxin A = enterotoxin = inflammation
      - Toxin B = cytotoxin = virulence factor (more dangerous than A)
    - 3% of community, 30% of hospitalised patients
    - Antibiotic related colitis (any but mainly cephalosporins, cipro and clindamycin)
    - Infection control – isolate and hand-washing
    - Treatment: PO vancomycin, stop antibiotics where possible

Question 16

Q

Answer

A

Pseudomembranous colitis - C.diff

Question 17

Q

Describe listeria monocytogenes infection.

Answer

A

Bad for pregnant women
Outbreaks of febrile gastroenteritis
ß-haemolytic, aesculin positive with tumbling-weed motility
Source: refrigerated food (“cold-enhancement”), unpasteurized dairy, vegetables (grows at 4ºC)
Symptoms: Watery diarrhoea, cramps, headache, fever, little vomiting
- At risk: perinatal infection, immunocompromised patients, elderly (confused)
  - Treatment: ampicillin, ceftriaxone, cotrimoxazole

Question 18

Q

Describe the enterobacteriaceae, what is the source toxins, types? What should be avoided?

Answer

A

Facultative anaerobes, glucose/lactose fermenters (LF), oxidase-negative
Escherichia coli (Traveler’s diarrhoea)
- Source: food/water contaminated with human faeces.
- Enterotoxins:
  - Heat labile stimulates adenyl cyclase and cAMP
  - Heat stable stimulates guanylate cyclase
  - Act on the jejunum/ileum not on colon
    - ETEC; toxigenic → main cause of traveller’s diarrhoea
    - EPEC; pathogenic → infantile diarrhoea
    - EIEC; invasive → dysentery
    - EHEC; haemorrhagic → O157:H7 EHEC: shiga-like verocytotoxin causes HUS
    - Avoid antibiotics

Question 19

Q

Describe salmonella infections. What are the antigens, species …

Answer

A

Non-lactose fermenters, H₂S producers (black colonies), TSI agar, XLD agar, selenite F broth
Antigens:
- Cell wall O (groups A-I)
- Flagellar H
- Capsular VI (virulence, antiphagocytic)

Three species – distinguished by disease caused

S type
S. enteritidis
S cholerasuis

Question 20

Q

Differentiate between S.typhi and S enteritides.

Question 21

Q

Describe shigella infection. What are the antigens? How does it spread? What does it cause? How should it be managed?

Answer

A

Non-lactose fermenters, non H2S producers, non-motile
Antigens:
- Cell wall O antigens
- Polysaccharide (groups A-D): S. sonnei, S. dysenteriae, S. flexneri (MSM)
  - The most effective enteric pathogen (low infectious dose 50)
  - No animal reservoir (human → human transmission)
  - No carrier states
  - Dysentery
    - Invading cells of mucosa of distal ileum and colon
    - Producing enterotoxin (Shiga toxin)
    - Avoid antibiotics (ciprofloxacin if required)

Question 22

Q

What are vibrios? What are the types?

Answer

A

Curved, comma shaped, late lactose fermenters, oxidase positive
- Vibrio cholerae
- Vibrio parahaemolyticus
- Vibrio vulnificus

Question 23

Q

Describe Vibrio cholerae

Answer

A

O1 group: epidemics, biotypes El Tor, Cholerae and serotypes Ogawa, Inaba, Hikojima
Non O1 group: sporadic or non-pathogens
Faeco-oral transmission inc. shellfish, oysters, shrimp
Colonisation of small bowel and secretion of enterotoxin with A and B subunit, causing persistent stimulation of adenylate cyclase
Causes massive diarrhoea (rice water stool) without inflammatory cells

Treat the losses: electrolyte replacement and fluids

Question 24

Q

Describe Vibrio parahaemolyticus

Answer

A

Ingestion of raw or undercooked seafood (i.e. oysters)
Major cause of diarrhoea in Japan or when cruising in the Caribbean
Self-limited for 3 days
Cholerae: grows in salty 8.5% NaCl
Treat with doxycycline

Question 25

Q

Describe Vibrio vulnificus

Answer

A

Cellulitis in shellfish handlers and fatal septicaemia with D+V in HIV patients
Treat with doxycycline

Question 26

Q

Describe campylobacter.

Answer

A

Curved, comma or S shaped; Microaerophilic
C. jejuni at 42 ºC
Oxidase positive, motile
Self-limiting but symptoms can last for weeks (20 days) – only tx if immunocompromised (macrolide)
Transmitted via contaminated food and water with animal faeces (poultry, meat, unpasteurised milk)
Enterotoxin (watery diarrhoea) with invasion (+/- blood)
Symptoms: Watery, foul smelling diarrhoea, bloody stool, fever and severe abdominal pain → treat with erythromycin or cipro if in the first 4-5days
Extra outcomes: GBS, ReA, Reiter’s

Question 27

Q

Describe Yersinia enterocolitica

Question 28

Q

Describe mycobacteria.

Answer

A

Will appear as gram variable
Always think of TB

Question 29

Q

Describe entamoeba histolytica.

Answer

A

Motile trophozoite in diarrhoea; Non-motile cyst in non-diarrhoeal illness
Killed by boiling, removed by water filters; 4 nuclei
No animal reservoir
Ingestion of cysts: trophos in ileum which colonize cecum and colon causing a “flask shaped” ulcer
Symptoms: dysentery, flatulence, tenesmus or in chronic form: weight loss +/- diarrhoea, liver abscess
Diagnosis
- Stool microbiology (wet mount, iodine and trichrome)
- Serology in invasive disease
  - Treat: metronidazole and paromomycin in luminal disease

Question 30

Q

Describe Giardia lamblia.

Answer

A

Trophozoite “pear shaped”; 2 nuclei
4 flagella and a suction disk
Ingestion of cyst from faecal-contaminated water and food
- Excystation at duodenum, tropho attaches, no invasion but malabsorption of protein and fat
  - Travellers (cruise), hikers, day care, mental hospitals, MSM
  - Symptoms: Foul smelling non-bloody diarrhoea, cramps, flatulence, no fever
  - Diagnosis: stool micro, ELISA, “string test”
  - Treatment: metronidazole

Question 31

Q

Describe Cryptosporidium parvum

Answer

A

Infects the jejunum
Severe diarrhoea in the immunocompromised (can cause outbreaks)
Oocysts seen in stool by modified Kinyoun acid fast stain
Treatment: reconstitution of immune system. Self-limiting

Question 32

Q

Describe norovirus.

Answer

A

Outbreaks
Low ID load (18-1000 viral particles) – lick lips on an infected ward is enough!
Environmental resilience (0-60 degrees)
No long-term immunity
G2.4 currently predominant strain

Question 33

Q

Describe rotavirus

Answer

A

dsRNA “wheel like”
Replicates in mucosa of small intestine
Secretory diarrhoea, no inflammation
Watery diarrhoea by stimulation of enteric nervous system
By age 6 most children worldwide have antibodies to at least one type
Exposure to natural infection twice confers lifelong immunity
- Huge economic burden worldwide

Question 34

Q

Describe adenovirus.

Answer

A

Types 40/41 cause non-bloody diarrhoea usually <2yrs of age. Any type in immunocompromised
Diagnosis: stool EM, antigen detection, PCR
- Poliovirus
- Enteroviruses (coxsackie, ECHO)
- Hepatitis A
  - Transmitted via faecal-oral route but main presentations from other systems

Question 35

Q

How should infection be prevented and controlled?

Answer

A

Targets for promotion
- Breastfeeding, improved weaning practice
- Clean water for drinking
- Safe disposal of stools of young children
- Precautions when travelling
- Food handling
- Public health notification
- Good handwashing

Question 36

Q

Explain the use of vaccines?

Answer

A

Cholera: serogroups O1 (Inaba, Ogawa, biotypes El Tor and classical), O139
- Inactivated, whole cell, contains all above + B subunit of toxin (PO)
- Live attenuated (PO) not recommended
- Campylobacter: military, infants, traveller, candidate vaccines exist
- ETEC: inactivated and live vaccines in trials
- Salmonella typhi: Vi capsular PS (IM) and (PO) live
- Rotavirus
  - Rotarix: live attenuated human strain monovalent, 2 (PO) doses
  - Rotateq: pentavalent, 3 (PO) doses, one bovine and four human strains
  - Rotashield and intussusception (8-20 weeks)
  - Age of vaccine is 6-12 weeks

Question 37

Q

Explain the need for Public Health.

Answer

A

Notifiable diseases = Campylobacter, Clostridium species, Listeria monocytogenes, Vibrio, Yersinia
Each trust to notify to local Health Protection Unit
Identify outbreaks in areas
Environmental Health Officers to inspect premises and take samples from environment and food