GI Infections Flashcards
What groups are most vulnerable to GI infections
Infants
Elderly
What are the reportable GI infections of note
Campylobacter Salmonella Shigella E.coli O157 Listeria Norovirus
No fever or low grade fever
No white blood cells in stool sample
Secondary diarrhoea
E.g. vibrio cholerae, ETEC, EAggEC, EPEC, EHEC
Fever
White blood cells in the stool sample (neutrophilia)
Inflammatory diarrhoea
E.g. campylobacter jejuni, shigella spp, non-typhoid salmonella serotypes, EIEC
Fever
White blood cells in stool sample (mononuclear cells)
Enteric fever
E.g. typhoidal salmonella serotypes
Enteropathogenic yersinia spp
Brucella spp
Incubation period for campylobacter
1-10 days
Disease duration of campylobacter
2-20 days
Most common source of campylobacter
Poultry
Incubation period for E.coli O157
1-5 days
Disease duration of e.coli O157
1-4 days
Incubation period of shigella
12-96 hours
Disease duration of shigella
5-7 days
Incubation period of salmonella
8-48 hours
Disease duration of salmonella
4-7 days
Incubation period of vibrio parahaemolyticus
24-72 hours
Disease duration of vibrio parahaemolyticus
2-10 days
Most common source of vibrio parahaemolyticus
Shellfish
Mechanism of disease of cholera toxins
It is a secretory diarrhoea toxin production
cAMP: opens Cl channel at the apical membrane of enterocytes
Efflux of Cl to lumen: loss of H2O and electrolytes
Mechanism of disease of superantigens
They are secretory diarrhoea-toxin production
Superantigens bind directly to T cell receptors and MHC class II molecules OUTSIDE the peptide binding site.
This leads to a massive cytokine production by CD4 cells (i.e. systemic toxicity and suppression of adaptive responses)
Host responses in enteric fever
Intestinal inflammation –> bacteraemia (in an immunocompromised patient) –> weak stimulation of acute phase responses (monocytes) –> no septic shock and no neutrophilia
Host responses in inflammatory (exudative) diarrhoea
Exudative inflammation –> bacteraemia (immunocompromised patient) –> detection of LPS by monocytes expressing TLR4 –> TNFa, IFNg, IL1B –> neutrophilia and septic shock
Features of staphylococcus 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
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
Bacillus cereus
Causes food poisoning
Gram positive rod: spore forming
Spores germinate in reheated fried rice (e.g. chinease fried rice)
Heat stable emetic toxin - not destroyed by reheating
Heat labile diarrhoeal toxin - food is not cooked to a high enough temperature
Causes: water non-bloody diarrhoea which is self-limited
Rare cause of bacteraemia in vulnerable population
Can cause cerebral abscesses
Clostridium botulinum
Gram positive anaerobe
Causes botulism
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
Clostridium pefringens infection
Gram positive anaerobe
Causes food poisoning
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
Clostridium difficile
Causes pseudomembranous colitis
Occurs in 3% general population, 30% of hospitalised patients
Antibiotic related colitis (any can cause it, but mainly cephalosporins, ciprofloxacin and clindamycin)
Avoidance involved infection control
Treatment: metronidazole, vancomycin, and stop the causative antibiotics where possible
Listeria monocytogenes infection
Outbreaks of febrile gastroenteritis
Beta 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
Enterobacteriacae infection
Facultative anaerobes, glucose/lactose fermenters (LF),
oxidase negative
Escherichia coli infection
Enterobacteriacae
Causes 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
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
Salmonella infection
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
S. enteritidis salmonella infection
Causes 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
S.typhi salmonella infection
Causes 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
Shigellae infection
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)
Vibrios infection
Curved, comma shaped, late lactose fermenters, oxidase positive.
Subtypes: cholera, parahaemolyticus, vulnificus
Vibrios cholera infection
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
Vibrio parahaemolytiocus infection
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..
Vibrio vulnificus infection
Cellulitis in shellfish handlers
Fatal septicaemia with D&V in HIV patients
Treat with doxycycline
Campylobacter infection
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)
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
Associated with GBS syndrome, reactive arthritis, Reiter’s ..
Yersinina enterocolitis infection
-Non lactose fermenter, prefers 4ºC “cold enrichment”
Transmitted via food contaminated with domestic animals excreta
Enterocolitis
Mesenteric adenitis
Associated with reactive arthritis , Reiter’s
Mycobacteria infection (M. tuberculosis, M, avium, intracellulare)
Will appear as gram variable
Always think of TB
Entamoeba histolytica infection
Protozoa Motile trophozoite in diarrhoea Non motile cyst in nondiarrhoeal illness Killed by boiling, removed by water filters 4 nuclei No animal reservoir Ingestion of cysts -->trophos in ileum -->colonize cecum, colon -->“flask shaped” ulcer
Dysentery,flatulence,
tenesmus
Chronic : wt loss,+/- diarrhoea
Liver abscess
Diagnosis: stool micro (wet mount, iodine and trichrome), serology in invasive disease
Treat : metronidazole + paromomycin in luminal disease
Giardia lamblia infection
Protozoa 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
Travellers, hikers,
day care, mental hospitals,
MSM
Foul smelling non
bloody diarrhoea, cramps
flatulence, no fever
Diagnosis : stool micro, ELISA, “string test”
Treatment: metronidazole
Cryptosporidium parvum infection
Protozoa infection
Infects the jejunum
Severe diarrhoea in the immunocomromised
Oocysts seen in stool by modified Kinyoun acid fast stain
Treatment : reconstitution of immune system
Norovirus unfection
Causes outbreaks Low ID (18-1000 viral particles) Environmental resilience (0-60 ºC) No long term immunity GII.4 currently predominant strain
Rotavirus infection
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
Adenovirus infection
Types 40, 41 cause non bloody diarrhoea <2yrs of age
Can affect any type in immunocompromised
Diagnosis : stool EM, antigen detection, PCR
Types: Poliovirus, Enteroviruses (coxsackie, ECHO), Hepatitis A
Best prevention tactics for GI infections
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
What vaccines are available against GI infections
Cholera
Campylobacter
ETEC
Salmonella typhi
Cholera vaccine
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 vaccine
Military, infants,traveller, candidate vaccines exist..
ETEC vaccine
Inactivated and live vaccines in trails
Salmonella typhi vaccine
Vi capsular PS (IM) and (PO)live
Rotavirus vaccines
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.
What are the public health implications in GI infections
Notifiable disease
Each trust to notify to local Health Protection Unit
Notifiable diseases: Campylobacter, Clostridium sp, Listeria monocytogenes, Vibrio, Yersinia
Identify outbreaks in areas
Environmental Health Officers to inspect premises and take samples from environment and food
