Micro - GI infections

Question 1

What are the types of clinical GI infection syndromes

Answer 1

Secretory diarrhoea: toxin production → Cl secretion into lumen → loss of water and electrolytes → D&V
- Watery diarrhoea with no fever
- Cholera, ETEC, EPEC, viruses

Inflammatory diarrhoea → inflammation and bacteraemia
- Bloody diarrhoea (dysentery), fever
- C. jejuni, shigella, non-typhoidal salmonella, EIEC

Enteric fever
- Fever, fewer GI symptoms
- Typhoidal salmonella, yerisinia, brucella

Question 2

What are the features of clostridium botulinum and what is the treatment

Answer 2

Gram +ve anaerobe
Canned/vacuum packed foods: Honey (kids),
beans (students)
Ingestion of preformed toxin (inactivated by cooking)
Blocks Ach release from peripheral nerves →
Descending paralysis (differentiates from GBS)

Tx: antitoxin

Question 3

What are the features of Clostridium perfringens infection

Answer 3

Gram +ve anaerobe
Normal flora of the colon, but not the small bowel where the enterotoxin acts
Reheated meats, 8-16hrs incubation
Watery diarrhoea + cramps, lasts 24hrs
Also causes gas-gangrene

Question 4

What are the features of Clostridium difficile infection and what is the treatment

Answer 4

Gram +ve anaerobe
2 exotoxins (A,B)
- Toxin A = enterotoxin = inflammation
- Toxin B = cytotoxin = virulence factor (more dangerous)
Pseudomembranous colitis
Suspect if severe diarrhoea + recent Hx of Abx (usually cephalosporins/fluorquinolones)

Tx: metronidazole, 2nd line vancomycin

Question 5

What are the features of bacillus cereus infection

Answer 5

Gram positive rods, spore-forming
Reheated rice (spore germinates)– suspect after re-heated takeout
Short incubation ~4hrs
Sudden vomiting and watery, non-bloody diarrhoea
Superantigen — short incubation (4hrs)
Increased cAMP— long incubation (18hrs)
Self-limiting
May cause cerebral asbcess

Question 6

What are the features of staph aureus infection

Answer 6

Gram +ve clusters of cocci on gram stain, catalase, coagulase +ve, yellow colonies on blood agar
Spread by skin lesions on food handlers
Produces enterotoxin (acts as superantigen → IL1/2
release)
Short incubation ~2hrs
Prominent vomiting, watery non-bloody diarrhoea
Self-limiting

Question 7

What are the features of E. Coli infection and how is it treated

Answer 7

Gram negative rod (Facultative anaerobes, glucose/lactose fermenters (LF), oxidase-negative)
Transmitted in faeces/contaminated water
ETEC: toxigenic, traveller’s diarrhoea
EIEC: invasive dysentery
EHEC: Haemorrhagic → HUS
HUS: Anaemia, thrombocytopenia, renal failure (0157:H7 toxin)
EPEC: Infantile diarrhoea (Paeds)

Tx: self-limiting, can treat with cipro

Question 8

What are the features of typhoidal salmonella infection and how is it treated

Answer 8

Typhi + paratyphi
Multiplies in Peyer’s patches, spreads ERS
Enteric fever: Constipation, fever, rose spots,
splenomegaly

Tx: IV ceftriaxone → PO azithromycin

Question 9

What are the features of non-typhoidal salmonella infection and how is it treated

Answer 9

Enteritides
Poultry, eggs, meat
Non-bloody diarrhoea, no fever

Tx: self-limiting, Ceftriaxone if required

Question 10

What are the features of shigella infection and how is it treated

Answer 10

No animal reservoir (human → human transmission)
Affects the distal ileum + colon → mucosal inflammation, fever, pain, bloody diarrhoea (dysentery)

Tx: self-limiting, cipro if required

Question 11

What are the features of vibrio infection

Answer 11

Curved, comma shaped, late lactose fermenters, oxidase positive

Cholera: Faeco-oral transmission (shellfish, oysters, shrimp). Rice water stool (massive diarrhoea without inflammation)
- Enterotoxin A and B subunit → persistent stimulation of adenylate cyclase

Parahaemolyticus: raw seafood (common in Japan)

Vulnificus: cellulitis in shellfish handlers

All self-limiting, treat dehydration, consider doxicyclin for para + vulni

Question 12

What are the features of campylobacter jejuni infection and how is it treated

Answer 12

Curved, comma or S shaped; Microaerophilic
Undercooked poultry (chicken at a BBQ)
Prodrome of fever and headache, then abdo cramps and bloody diarrhoea
Lasts ~10d
Associated with GBS, reactive arthritis, Reiter’s

Tx: erythromycin or cipro in first 5 days

Question 13

What are the features of listeria monocytogenes infection and how is it treated

Answer 13

Refrigerated food, unpasteurised dairy
Perinatal infection
Severe infection in immunocompromise
Water diarrhoea, cramps, headaches, fever

Tx: Ampicillin

Question 14

What are the features of entaemoeba histolytica infection and how is it treated

Answer 14

Motile trophozoite in diarrhoea; Non-motile cyst in non-diarrhoeal illness
Flask-shaped ulcer on histology with 4 nuclei
Dysentery, flatulence, tenesmus
More common in MSM

Tx: metronidazole

Question 15

What are the features of giardia lamblia infection and how is it treated

Answer 15

Pear-shaped trophozoite with 2 nuclei, 4 flagella and suction disc
Causes malabsorption of fat → foul-smelling non-bloody diarrhoea

Tx: metronidazole

Question 16

What are the features of cryptosporidium parvum infection and how is it treated

Answer 16

Severe diarrhoea in immunocompromised
Infects jejunum
Oocysts seen in stool by modified Kinyoun acid fast stain

Tx: paromomycin

Question 17

What are the features of viral causes of GI infection

Answer 17

Norovirus: secretory diarrhoea in adult outbreaks, no long-term immunity, low ID load with environmental resilience
Adenovirus: secretory diarrhoea <2yo
Rotavirus: secretory diarrhoea <6yo, dsRNA “wheel like”, exposure 2x → lifelong immunity

All self-limiting

Question 18

Define gastroenteritis

Answer 18

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 19

Define diarrhoea

Answer 19

loose or watery stool, ≥3 times in 24 hours

Question 20

What defines acute, persistent, and chronic diarrhoea

Answer 20

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 21

What are the differences between small and large bowel diarrhoea

Answer 21

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 22

How does cholera toxin work

Answer 22

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

Question 23

What are superantigens

Answer 23

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

Question 24

What investigations should be done for GI infections

Answer 24

Stools testing – cultures or independent methods (i.e. multiplex molecular PCR)
Enteric fever – blood and stool tested by culturing and independent testing methods (BM, duodenal fluid and urine)
Parasites – stools for microscopy and culture (inc. ova cysts and parasites)

Question 25

What are the extra-intestinal manifestations for the following:
Salmonella, yersinia
Campylobacter, Yersinia
Shigella, Campylobacter, Yersinia
STEC, Shigella
Yersinia, Campylobacter, Salmonella, Shigella
Salmonella, Shigella, Campylobacter, yersinia, (giardia, Cyclospora cayetanensis)
Listeria, salmonella

Answer 25

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): meningitis

Question 26

What are the features of yersinia enterocolitica

Answer 26

Non-lactose fermenter, prefers 4ºC “cold enrichment”
Transmitted via food contaminated with domestic animal’s excretions
Enterocolitis, mesenteric adenitis and associated reactive arthritis, Reiter’s

Question 27

Which causes of gastroenteritis are notifiable disease

Answer 27

Campylobacter
Clostridium
Listeria monocytogenes
Vibrio
Yersinia