GIS26 Gastrointestinal Tract Infections Flashcards
Normal intestinal defence
- Gastric acidity
- Intestinal motility
- Normal intestinal microbiota: Colonisation resistance
- Specific immunity: Phagocyte, Cell-mediated, Humoral
Microbiology of the intestine
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:
- Colonisation resistance
- Intra-abdominal infections (secondary peritonitis, intraperitoneal abscess, cholecystitis, cholangitis, liver abscess), Pelvic infection, UTI
Clinical approach to infectious diarrhoea
- 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 - Infectious / Non-infectious diarrhoea
- Community-acquired / institutional? Common-source outbreaks?
- 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
Control of enteric infections
- Public health measures
- improved water supply, sanitation, sewage disposal
- quality control of commercial products - Non-specific host factors
- personal hygiene
- judicious use of antacids, anti-motility drugs, antimicrobial - Surveillance, outbreak investigation
- Vaccines
- **Typhoid fever
- **Cholera
- ***Rotavirus
- Hepatitis A and E
Principles of therapy for infectious diarrhoea
- Fluid replacement (oral rehydration solution effective unless severe vomiting / impairment of consciousness)
- Antibiotics (only when indicated)
- Antimotility agents (***avoided in invasive infections)
- Early detection and treatment of complications
Pathogenesis of enteric infections
- Enteric bacterial toxins
- Non-inflammatory enteric infection
- Inflammatory enteric infection
- Penetrating enteric infection
Enteric bacterial toxins
- Secretory toxins
- Cholera toxin (Vibrio cholerae)
- Enterotoxigenic E. coli - Cytotoxins
- Shiga toxin (Shigella)
- Verocytotoxin (enterohaemorrhagic E. coli)
- Clostridium difficile - Neurotoxins
- Clostridium botulinum
- S. aureus
- Bacillus cereus
Non-inflammatory enteric infections vs Inflammatory enteric infection vs Penetrating enteric infection
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
Common enteric pathogens and infections
- Staphylococcus aureus, Bacillus cereus
- Vibrio, Aeromonas, Plesiomonas
- Diarrhoeagenic E. coli
- Campylobacter
- Salmonella
- Shigella
- Viral gastroenteritis
- Antibiotic associated diarrhoea
Staphylococcus aureus, Bacillus cereus
- 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
Vibrio, Aeromonas, Plesiomonas
- 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
6 types of Diarrhoeagenic E. coli
- Enterotoxigenic (ETEC)
—> 2 toxins (secretory toxin) —> watery diarrhoea
- traveller’s diarrhoea - Enteropathogenic (EPEC)
—> watery diarrhoea
- infantile diarrhoea (in nurseries) - 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 - Enteroinvasive (EIEC)
—> developing world
- dysentery - Enteroaggregative (EAggEC)
- diarrhoea in adults and children - Diffusely adherent (DAEC)
- diarrhoea in children
Enterohaemorrhagic / verocytotoxigenic / Shiga toxin-producing (EHEC / VTEC / STEC)
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
Campylobacter
- 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
Salmonella
Gram -ve Bacilli
Pathogenesis:
- Survival inside phagocytic cells
- ***Vi antigen of Salmonella Typhi: polysaccharide —> associated with resistance to phagocytosis and complement-mediated lysis
- various toxins
Salmonella gastroenteritis
- 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
Enteric fever
Syndrome of acute illness characterised by fever, abdominal pain, headache, relative bradycardia, sometimes skin rash, splenomegaly, leukopenia
Etiology:
-
**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 - Paratyphoid fever (Salmonella paratyphi A, B, C)
- 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)
Treatment of salmonellosis
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
Prevention and control of salmonellosis
- special attention to food and water supply, sewage disposal and food handlers
- 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
Shigella
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
Viral gastroenteritis
- Rotavirus
- Norovirus
- Enteric adenovirus
- Caliciviruses (sapovirus)
- Coronavirus
Rotavirus
- 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:
- Antigen detection by commercial kits (ELISA, latex agglutination)
- RT-PCR
- Electron microscopy (not routinely performed for diagnosis)
Treatment:
- adequate hydration
Vaccines:
- ***available
Norovirus
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
Antibiotic-associated diarrhoea
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)
Summary
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
Treatment summary
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
Watery diarrhoea vs Dysentery
Water diarrhoea:
- S. aureus, B. cereus
- ETEC
- EPEC
- V. cholerae
- C. diff
- Salmonella Typhi
Dysentery:
- ***EHEC
- (Campylobacter)
- ***Shigella
- Salmonella Non-typhi
