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GIS > GIS26 Gastrointestinal Tract Infections > Flashcards

GIS26 Gastrointestinal Tract Infections Flashcards

1
Q

Normal intestinal defence

A
  1. Gastric acidity
  2. Intestinal motility
  3. Normal intestinal microbiota: Colonisation resistance
  4. Specific immunity: Phagocyte, Cell-mediated, Humoral
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2
Q

Microbiology of the intestine

A

Stomach: (bacterial count directly related to pH of stomach content)

  • α-haemolytic streptococci
  • lactobacilli
  • yeasts
  • swallowed oral bacteria

Duodenum:

  • α-haemolytic streptococci
  • lactobacilli
  • transitory oral bacteria

Ileum:
- ↑ number towards distal ileum

Colon:

  • over 1000 cultivable species, many more not been cultured in vitro
  • ***Anaerobes: 96-99%

Importance:

  1. Colonisation resistance
  2. Intra-abdominal infections (secondary peritonitis, intraperitoneal abscess, cholecystitis, cholangitis, liver abscess), Pelvic infection, UTI
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3
Q

Clinical approach to infectious diarrhoea

A
  1. Symptomatology
    - incubation period
    - **vomiting
    - **    nature of stool (soft, watery; blood, mucus; frequency)
    - abdominal symptoms
    - systemic symptoms, neurological / renal manifestations
    - diarrhoea as a symptom of other systemic infections / diseases
  2. Infectious / Non-infectious diarrhoea
  3. Community-acquired / institutional? Common-source outbreaks?
  4. Risk factors
    - **food history
    - **    travel history
    - animal contacts
    - drugs
    - HIV infections / compromised host?
  • **5. Investigations and laboratory diagnosis
  • ***stool: routine bacterial culture; detection of viruses and parasites
  • ***blood: culture, serology
  • ***endoscopy: histopathology
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4
Q

Control of enteric infections

A
  1. Public health measures
    - improved water supply, sanitation, sewage disposal
    - quality control of commercial products
  2. Non-specific host factors
    - personal hygiene
    - judicious use of antacids, anti-motility drugs, antimicrobial
  3. Surveillance, outbreak investigation
  4. Vaccines
    - **Typhoid fever
    - **    Cholera
    - ***Rotavirus
    - Hepatitis A and E
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5
Q

Principles of therapy for infectious diarrhoea

A
  1. Fluid replacement (oral rehydration solution effective unless severe vomiting / impairment of consciousness)
  2. Antibiotics (only when indicated)
  3. Antimotility agents (***avoided in invasive infections)
  4. Early detection and treatment of complications
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6
Q

Pathogenesis of enteric infections

A
  1. Enteric bacterial toxins
  2. Non-inflammatory enteric infection
  3. Inflammatory enteric infection
  4. Penetrating enteric infection
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7
Q

Enteric bacterial toxins

A
  1. Secretory toxins
    - Cholera toxin (Vibrio cholerae)
    - Enterotoxigenic E. coli
  2. Cytotoxins
    - Shiga toxin (Shigella)
    - Verocytotoxin (enterohaemorrhagic E. coli)
    - Clostridium difficile
  3. Neurotoxins
    - Clostridium botulinum
    - S. aureus
    - Bacillus cereus
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8
Q

Non-inflammatory enteric infections vs Inflammatory enteric infection vs Penetrating enteric infection

A

Non-inflammatory enteric infections:

  • Enterotoxin-mediated (usually ***Secretory toxins)
  • location: ***Proximal small bowel
  • illness: ***Water diarrhoea / Vomiting
  • stool examination: ***NO faecal leukocytes
  • e.g. Vibrio cholerae, ETEC, Clostridium perfringens, Bacillus cereus, S. aureus

Inflammatory enteric infection:

  • **Local invasion into mucosa, **Cytotoxin-mediated
  • location: mainly ***Colon
  • illness: ***Dysentery (bloody diarrhoea)
  • stool examination: ***Faecal neutrophil ++
  • e.g. Shigella, non-typhoidal salmonellae, Campylobacter, Entamoeba histolytica

Penetrating enteric infection:

  • Distant / ***systemic infections
  • location: ***Distal small bowel (terminal ileum)
  • illness: ***Enteric fever
  • stool examination: ***Faecal mononuclear leukocytes +
  • e.g. Salmonella Typhi
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9
Q

Common enteric pathogens and infections

A
  1. Staphylococcus aureus, Bacillus cereus
  2. Vibrio, Aeromonas, Plesiomonas
  3. Diarrhoeagenic E. coli
  4. Campylobacter
  5. Salmonella
  6. Shigella
  7. Viral gastroenteritis
  8. Antibiotic associated diarrhoea
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10
Q

Staphylococcus aureus, Bacillus cereus

A
  • ingestion of heat-stable pre-formed toxin
  • short incubation period (1-6 hours)
  • main symptoms: **nausea and vomiting, **watery diarrhoea
  • mild and self-limiting illness
  • S. aureus: Enterotoxins. contamination of food by food handler
  • B. cereus (short incubation type): Germination of spores in food
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11
Q

Vibrio, Aeromonas, Plesiomonas

A
  • Gram -ve
  • Curved
  • Facultatively anaerobic
  • Oxidase +ve
  • motile by single polar flagellum
  • widely distributed in ***natural water bodies

Vibrio cholerae:

  • O1, O139 —> severe disease, epidemic potential
  • non-O1, non-O139 —> sporadic cases of diarrhoea
  • Pathogenesis: ***Cholera toxin (Secretory toxin)

Cholera:
Presentation:
- very profuse watery diarrhoea (classic ***rice water stool)

Diagnosis:

  • clinical
  • laboratory (culture on ***TCBS medium)

Treatment:

  • ***Antibiotics (shorten duration of diarrhoea + reduces fluid loss e.g. tetracycline, ciprofloxacin)
  • Adequate fluid replacement

Prevention:

  • clean water sources, boiling of drinking water
  • immunisation: traditional killed vaccines (relatively ineffective), newer oral vaccines: available but not 100% effective

Vibrio parahaemolyticus

  • very common cause of bacterial foodborne infection in HK (associated with community outbreaks)
  • commoner in summer months
  • milder infections: self-limiting, may not require antibiotics
  • Tetracycline group of antibiotics may be used if needed
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12
Q

6 types of Diarrhoeagenic E. coli

A
  1. Enterotoxigenic (ETEC)
    —> 2 toxins (secretory toxin) —> watery diarrhoea
    - traveller’s diarrhoea
  2. Enteropathogenic (EPEC)
    —> watery diarrhoea
    - infantile diarrhoea (in nurseries)
  3. Enterohaemorrhagic / Verocytotoxigenic / Shiga toxin-producing (EHEC / VTEC / STEC)
    —> person-to-person transmission in day care setting
    - haemorrhagic colitis (bloody diarrhoea / dysentery) (cytotoxin)
    - haemolytic uraemic syndrome
    - thrombotic thrombocytopenic purpura
  4. Enteroinvasive (EIEC)
    —> developing world
    - dysentery
  5. Enteroaggregative (EAggEC)
    - diarrhoea in adults and children
  6. Diffusely adherent (DAEC)
    - diarrhoea in children
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13
Q

Enterohaemorrhagic / verocytotoxigenic / Shiga toxin-producing (EHEC / VTEC / STEC)

A

Commonest serotype:
- O157:H7 —> colonic commensal in the cattle

Outbreaks:

  • Undercooked ground beef
  • Contaminated drinking water
  • Unpasteurised milk
  • Contaminated food

Pathogenesis:
- ***Verocytotoxins

Laboratory detection: differential media

  • sorbitol ***MacConkey agar (mainly for O157:H7, does not reliably detect non-O157 STEC)
  • PCR

Syndromes:

  • asymptomatic infection
  • self-limiting diarrhoea
  • ***blood diarrhoea
  • ***haemorrhagic colitis (little to no fever)

Complications:
- ***haemolytic uraemic syndrome (low RBC, low platelet, acute kidney failure)

Management:

  • supportive
  • antibiotics + anti-diarrhoeals ***NOT indicated
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14
Q

Campylobacter

A
  • Microaerophilic
  • Gram -ve
  • Spiral
  • Motile
  • culture: requires selective media + ***microaerophilic environment (5% O2)
  • Intestinal + extraintestinal infections
  • worldwide ***zoonosis: transmission: improperly prepared animal products; occasionally person-to-person
  • Treatment:
    —> ***Macrolides
    —> Fluid and electrolyte replacement
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15
Q

Salmonella

A

Gram -ve Bacilli

Pathogenesis:

  1. Survival inside phagocytic cells
  2. ***Vi antigen of Salmonella Typhi: polysaccharide —> associated with resistance to phagocytosis and complement-mediated lysis
  3. various toxins
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16
Q

Salmonella gastroenteritis

A
  • Nausea, vomiting, diarrhoea
  • severity variable
  • usually ***self-limiting
  • fever usually resolves in 48-72 hours
  • after resolution of gastroenteritis, mean duration of carriage of non-typhoidal salmonellae in stool is 4-5 weeks without treatment
  • ***Disseminated infections due to non-typhoidal salmonellae
    —> important cause of infection in immunocompetent / immunocompromised patients e.g. bacteraemia, mycotic aneurysm, osteomyelitis, abscesses
17
Q

Enteric fever

A

Syndrome of acute illness characterised by fever, abdominal pain, headache, relative bradycardia, sometimes skin rash, splenomegaly, leukopenia

Etiology:

  1. **Typhoid fever (Salmonella enterica serotype Typhi) (commonest)
    —> early symptom: constipation / diarrhoea
    —> untreated: last for 4 weeks before dying / recovery, **    rose spots, **splenomegaly, hepatomegaly, leukopenia
    —> complications: **    intestinal haemorrhage, intestinal perforation
  2. Paratyphoid fever (Salmonella paratyphi A, B, C)
  3. Yersinia

Diagnosis:
- clinical
- laboratory
—> ***Blood culture (>80% positive in 1st week)
—> Stool culture (late in 2nd to 3rd week)
—> Urine culture (usually late in the course and low positive rate)
—> Bone marrow culture (high positive rate but more invasive)
—> Serological test: Widal’s test (4-fold rise in titre necessary, often not useful clinically because of sensitivity and specificity issues)

18
Q

Treatment of salmonellosis

A

Gastroenteritis:

  • Fluid replacement
  • Antibiotics ***NOT always needed, for high risk patients / severe disease
Typhoid fever and systemic infections:
- Antibiotics ***indicated
—> 3rd cephalosporins (Ceftriaxone, Cefotaxime)
—> Fluoroquinolones
—> Azithromycin
19
Q

Prevention and control of salmonellosis

A
  1. special attention to food and water supply, sewage disposal and food handlers
  2. vaccination against Salmonella Typhi
    - ***Vi polysaccharide vaccine (only one available in HK)
    - heat-killed phenol-treated vaccine: limited efficacy
    - Ty21a vaccine: live-attenuated oral vaccine
20
Q

Shigella

A

4 types:

  • S. dysenteriae
  • S. flexneri
  • S. boydii
  • S. sonnei
  • very low infectious dose —> ***highly contagious
  • invasive disease —> invasion and destruction of intestinal mucosa

Transmission:
—> water / food-borne
—> person-to-person transmission

Bacillary ***dysentery:

  • vomiting
  • diarrhoea
  • ***blood and mucus in stool
  • abdominal pain, fever
  • urgency, tenesmus (recurrent inclination to give bowel).
  • without antibiotic, faecal excretion lasts 1-4 weeks

Treatment:

  • Ampicillin
  • Cotrimoxazole
  • Nalidixic acid
  • Fluoroquinolone
  • Azithromycin
  • 3rd generation cephalosporin
  • high prevalence of resistance to older antibiotics

Control:

  • Safe water supply. Chlorination of potable water and proper sanitation
  • Removal of persons with diarrhoea from food handling, appropriate refrigeration and cooking of food
  • Effective hand-washing
  • Contact precautions in hospitals and institutions
21
Q

Viral gastroenteritis

A
  1. Rotavirus
  2. Norovirus
  3. Enteric adenovirus
  4. Caliciviruses (sapovirus)
  5. Coronavirus
22
Q

Rotavirus

A
  • commonest enteric viral pathogen in ***young children (commonest cause of nosocomial infectious gastroenteritis in paediatric patients)
  • direct patient-to-patient spread / through fomites
  • Winter / Spring: highest incidence

Diagnosis:

  1. Antigen detection by commercial kits (ELISA, latex agglutination)
  2. RT-PCR
  3. Electron microscopy (not routinely performed for diagnosis)

Treatment:
- adequate hydration

Vaccines:
- ***available

23
Q

Norovirus

A

Transmission:

  • foodborne (esp. contaminated seafood like raw oyster)
  • waterborne
  • person-to-person (faeco-oral, aerosol from vomitus)
  • sporadic cases / outbreaks of gastroenteritis, commonly in ***winter months (winter vomiting disease)

Incubation period:
- 12-48 hrs, lasts 12-60 hrs

Symptoms:

  • ***acute onset of nausea, vomiting (can be severe)
  • abdominal cramps
  • diarrhoea

Diagnosis:

  • ***RT-PCR (method of choice)
  • electron microscopy (not routinely performed)

Treatment:
- supportive

24
Q

Antibiotic-associated diarrhoea

A

Commonest cause: Clostridium difficile

  • ***Gram +ve
  • anaerobic
  • spore-forming
  • normal flora in 3% of health adults (colonisation rate increased in hospitalised / newborns; acquired by cross-infection)
  • Use of antibiotic change normal colonic flora
    —> overgrowth of C. difficile

Clostridium difficile colitis:

  • **Pathogenesis:
  • toxin A
  • toxin B

Pathology
- inflammation of colonic mucosa +/- pseudo-membrane formation

Clinical features

  • watery / mucoid stool +/- blood
  • abdominal pain
  • fever
  • abdominal tenderness
  • leukocytosis
  • ***Pseudomembranous colitis: most severe

Diagnosis:

  • ***sigmoidoscopy
  • stool culture for C. difficile
  • detection of cytotoxin (tissue culture)
  • antigen detection in stool (commercial kits)
  • PCR

Treatment:

  • ***oral Vancomycin
  • oral Fidaxomicin
  • Metronidazole (inferior efficacy)
25
Q

Summary

A 
S. aureus: Enterotoxin
B. cereus
- non-inflammatory
- self-limiting
- watery diarrhoea

V. cholerae

  • contaminated natural water
  • O1-O139: rice watery stool
  • TCBS medium
  • Tetracycline

EHEC:

  • person-to-person, contaminated food
  • Verocytotoxin
  • Haemorrhagic colitis
  • Haemolytic uraemic syndrome
  • Sorbitol MacConkey agar
  • self-limiting
  • NO antibiotic

Campylobacter:

  • microaerophilic
  • worldwide zoonosis
  • Macrolide

Salmonella:

  • Non-typhoidal: disseminated infection
  • Salmonella gastroenteritis: self-limiting, antibiotic for severe
  • Enteric fever: Typhi (Typhoid fever), Paratyphi (Paratyphoid fever), Yersinia
  • Typhoid fever: rose spot, splenomegaly, hepatomegaly, leukopenia
  • blood culture
  • 3rd gen Cephalosporin
  • Fluoroquinolone
  • Azithromycin
  • Vi polysaccharide vaccine

Shigella (dysenteriae)

  • Bacillary dysentery
  • Invasive: destruction of mucosa
  • highly contagious, person-to-person, food
  • Treatment only for dysentery
  • 3rd gen Cephalosporin
  • Fluoroquinolone
  • Azithromycin
  • Ampicillin

Rotavirus:

  • Nosocomial paediatric
  • antigen detection by kit
  • vaccine available

Norovirus:

  • winter
  • food/water, person-to-person
  • RT-PCR

Antibiotic-associated diarrhoea:

  • C. Difficile overgrowth
  • gram +ve anaerobic
  • normal flora
  • C. difficile colitis: Toxin A, Toxin B
  • colonic mucosal inflammation + Pseudomembrane
  • leukocytosis
  • watery/mucoid stool
  • Pseudomembranous colitis
  • Stool culture, cytotoxin detection, sigmoidoscopy
  • Oral Vancomycin, Metronidazole
26
Q

Treatment summary

A

Cholera: Tetracycline
Campylobacter: Macrolide
Salmonella typhi: 3rd gen Cephalosporin, Fluoroquinolone, Azithromycin
Shigella: 3rd gen Cephalosporin, Fluoroquinolone, Azithromycin, Ampicillin
C. diff: Oral Vancomycin, Metronidazole
ETEC: Co-trimoxazole

EHEC, Salmonella gastroenteritis, Viral infection NO treatment

27
Q

Watery diarrhoea vs Dysentery

A

Water diarrhoea:

  • S. aureus, B. cereus
  • ETEC
  • EPEC
  • V. cholerae
  • C. diff
  • Salmonella Typhi

Dysentery:

  • ***EHEC
  • (Campylobacter)
  • ***Shigella
  • Salmonella Non-typhi

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