GI Infection Flashcards
What is the epidemiology of GI infections?
Underreporting of GI infections
Most are self limiting <24 hours, patients do not seek healthcare
Developing countries-outbreaks, cholera especially in war torn countries with no access to clean drinking water and sanitation
Most vulnerable groups: Infants, elderly
Reportable: Campylobacter, Salmonella, Shigella, E.Coli 0157, Listeria, Norovirus
What is the difference between secretory diarrhoea, inflammatory diarrhoea and enteric fever?
What is the incubation, duration and cause of campylobacter?
1-10 days
2-20
Poultry
What is the incubation, duration and cause of EColi 0157?
1-5 days
1-4
HUS, verotoxin
What is the incubation, duration and cause of Shigella?
12-96hrs
5-7
Small infective dose, outbreaks
What is the incubation, duration and cause of Salmonella (non typhoid)?
8-48h
4-7
Rare cause systemic dx
What is the incubation, duration and cause of vibro prahaemolyticus?
24-72h
2-10
Shellfish
What is the incubation, duration and cause of vibrio cholera?
1-5 days
Variable
Ricewater, endemic
What is the incubation, duration and cause of Bacillus Cereus?
1-6h
<1 day
Heat stable emetic toxin (rice)
What is the incubation, duration and cause of Staph Aureus?
2-7h
<1day
Preformed toxin
How do secretory toxins work?
cAMP: opens Cl channel at the apical membrane of enterocytes
>> efflux of Cl to lumen; loss of H2O and electrolytes
How do superantigens work?
Superantigens bind directly to
T-cell receptors and
MHC molecules;
outside the peptide binding site
>> massive cytokine production by CD4 cells ie systemic toxicity and suppression of adaptive response
What is the difference between inflammatory diarrhoea and enteric fever?
Host responses in bacteraemia:
Inflammatory (exudative ) diarrhoea
Vs
Enteric fever; interstitial inflammation
What is Staph Aureus?
Food Poisoning
- 1/3 population chronic carriers, 1/3 transient
- Spread by skin lesions on food handlers
- Catalase, coagulase positive Gram positive coccus
- Appears in tetrads, clusters on Gram stain
- Yellow colonies on blood agar
How dose S Aureus work?
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
Don’t treat, self limited
What does Bacillus cereus do?
•Bacillus cereus : food poisoning
Spores germinate in reheated fried rice
Gram positive rods: spore forming
What is Bacillus Cereus?
- Gram positive rod-spores
- Heat stable emetic toxin
-not destroyed by reheating
- Heat labile diarrhoeal toxin
- -food is not cooked to a high enough temperature
and
- watery non bloody diarrhoea; self limited
- Rare cause of bacteremia in vulnerable population
- Can cause cerebral abscesses
What is clostridia botulinum?
- Source : canned or vacuum packed food (honey / infants)
- Ingestion of preformed toxin (inactivated by cooking)
- Blocks Ach release from peripheral nerve synapses
- Treatment with antitoxin
What is clostridium pefringens?
- Source : reheated food (meat)
- Normal flora of colon but not small bowel, where the enterotoxin acts (superantigen)
- Incubation 8-16hrs
- Watery diarrhoea, cramps,little vomiting lasting 24hrs
Why is pseudomembranous colitis bad?
- 3%, 30% of hospitalised patients
- Antibiotic related colitis (any but.. mainly cephalosporins, cipro and clindamycin)
How do you manage C diff?
- Infection control
- Treatment : (PO) metronidazole, vancomycin, stop antibiotics where possible
What is Listeria monocytogenes?
- Outbreaks of febrile gastroenteritis
- ß haemolytic, aesculin positive with tumbling motility
- Source : refrigerated food (“cold enhancement”),i.e. unpasteurised dairy, vegetables
- Grows at 4 ºC GI watery diarrhoea, cramps, headache, fever, little vomiting
- Perinatal infection, immunocompromised patients
- Treatment : ampicillin
What is enterobacteriacae?
Facultative anaerobes, glucose/lactose fermenters (LF),
oxidase negative
What is E coli?
- Traveller’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 jejeunum, ileum not on colon
What are the types of E coli?
- 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
What is salmonellae?
- Non lactose fermenters,
- H2S producers,
- TSI agar,
- XLD agar,selenite F broth
- Antigens:
- cell wall O (groups A-I)
- flagellar H
- capsular Vi (virulence, antiphagocytic)
•Three species :
- S. typhi (and paratyphi) -S.enteritidis
- S.cholerasuis
What is S enteritidis?
Enterocolitis
- transmitted from poultry, eggs, meat
- invasion of epi- and sub-epithelial, tissue of small and large bowel
- bacteraemia infrequent
- self limited non bloody diarrhoea ,usually no treatment
- Stool positivity
What is S typhi?
Typhoid (enteric) fever
- transmitted only by humans
- multiplies in Payer’s patches,
- spreads ERS
- bacteraemia, 3% carriers
- Slow onset, fever and constipation,
- splenomegaly,rose spots,
- anaemia, leucopaenia,
- bradycardia, haemorrhage and
- perforation
- Blood culture positive
- Treatment : ceftriaxone
What is Shigellae?
- 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 ID 50)
- No animal reservoir
- No carrier state
- Dysentery
- invading cells of mucosa of distal ileum and colon
- producing enterotoxin (Shiga toxin)
Avoid antibiotics (ciprofloxacin if required)
What are Vibrios?
Curved, comma shaped, late lactose fermenters, oxidase positive.
What is Vibrio Cholerae?
- O1 group: epidemics, biotypes El Tor, Cholerae and serotypes Ogawa, Inaba, Hikojima
- Non O1 group: sporadic or non pathogens
- Transmitted by contamination of water and food from human faeces ( 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
What is Vibrioe parahaemolyticus?
- Ingestion of raw or undercooked seafood (ie oysters),
- major cause of diarrhoea in Japan..or when cruising in the Carribean.. ,
- self limited for 3 days
- cholerae : grows in salty 8.5% NaCl.
What is Vibrio vulnificus?
- cellulitis in shellfish handlers
- fatal septicaemia with D+V in HIV patients
How do you treat vibrios diarrhoea?
Doxycycline
What is campylobacter?
- Curved, comma or S shaped
- Microaerophilic
- C.jejuni at 42 ºC
- oxidase pos ,motile
- Self limiting but symptoms can last for weeks (20 days)
- Only treat if immunocompromised (macrolide)
Why is campylobacter bad?
- Transmitted via contaminated food and water with animal faeces ( poultry, meat,unpast. milk)
- ? Enterotoxin (watery diarrhoea) ? Invasion (+/- blood)
- Watery, foul smelling diarrhoea, bloody stool, fever and severe abdo pain
- Treat with erythromycin or cipro if in the first 4-5days
GBS syndrome, reactive arthritis, Reiter’s
What is Yersinia enterocolitica?
- Non lactose fermenter, prefers 4ºC “cold enrichment”
- Transmitted via food contaminated with domestic animals excreta
- enterocolitis
- mesenteric adenitis
- associated with reactive arthritis , Reiter’s
What is mycobacteria?
- will appear as Gram variable
- always think of TB
What is entamoeba histolytica?
- motile trophozoite in diarrhoea
- non motile cyst in nondiarrhoeal illness
- Killed by boiling, removed by water filters
- 4 nuclei
- No animal reservoir
What are the clinical features of entamoeba histolytica?
Ingestion of cysts >> trophos in
ileum >> colonize cecum, colon >> “flask shaped” ulcer
-dysentery,flatulence,
tenesmus
- chronic : wt loss,+/- diarrhoea
- liver abscess
How do you diagnose entamoeba histolytica?
-stool micro (wet
mount, iodine and trichrome )
-serology in invasive disease
Treat : metronidazole + paromomycin in luminal disease
What is Giardia lamblia?
- trophozoite “pear shaped”
- 2 nuclei
- 4 flagellas and a suction disk
- Ingestion of cyst from fecally contaminated water,food
- Excystation at duodenum
- tropho attaches
- no invasion
- malabsorption of protein and
fat
Who gets giardia and how do we manage it?
•Travellers, hikers,
day care, mental hospitals,
MSM
•foul smelling non
bloody diarrhoea, cramps
flatulence, no fever
- Diagnosis : stool micro, ELISA, “string test”
- Treatment :metronidazole
What is Cryptosporidium parvum and how is it managed?
- Infects the jejunum
- Severe diarrhoea in the immunocomromised
- Oocysts seen in stool by
modified Kinyoun acid fast stain
Treatment : reconstitution of immune system
What is Norovirus?
- outbreaks
- Low ID (18-1000 viral particles)
- Environmental resilience (0-60 ºC)
- No long term immunity
- GII.4 currently predominant strain
What is rotavirus?
- 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
What is adenovirus?
Types 40, 41 cause non bloody diarrhoea <2yrs of age
Any type in immunocompromised
What are the other viruses?
- Poliovirus
- Enteroviruses (coxsackie, ECHO)
- Hepatitis A
transmitted via faecal-oral route but main presentations from other systems
What is this?
Small bowel in viral GI infection
What are 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
–Good handwashing
–Good handwashing
Which vaccines exist?
•Cholera : serogroups O1(Inaba , Ogawa, biotypes El Tor and classical), O139
a. Inactivated, whole cell, contains all above + B subunit of toxin (PO)
b. 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
What is the rotavirus vaccine?
- 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
When does public health get involved?
- Notifiable disease
- Each trust to notify to local Health Protection Unit
- Campylobacter, Clostridium sp, Listeria monocytogenes, Vibrio, Yersinia
- Identify outbreaks in areas
- Environmental Health Officers to inspect premises and take samples from environment and food
What is gastroenteritis?
Rapid onset diarrhoeal illness lasting less than 2 weeks and has to be loose and 3+ times a day.
What are the risk factors of GI infections?
Foodborne
Expsoure related
Host related
What is Diarrhoea?
Loose or watery stools passed at least 3 times in 24 hours which can be acute (<14 days), persistent (14-29 days) or chroni (>30d).
What’s the difference between small bowel and large bowel diarrhoea?
Small bowel = watery, crampy pain, large volume, bloating, gas. Less likely to have fever/ blood/ inflammatory cells in the stool.
Large bowel = small volume, painful stool with blood, mucus, inflammatory cells and fever.
What condition can salmonella cause?
Aortitis
