Flashcards in GI Infections Deck (71):
What is the concern in developing countries?
Outbreaks such as cholera.
No access to clean drinking water and sanitation
Most vulnerable children and elderly
What are the reportable infections?
Campylobacter, salmonella, shigella, E. coli 0157, listeria, norovirus
What age group tend to be the most infected but not the most vulnerable?
What is the first clinical syndrome?
No fever, low grade, no WBC in stool.
Cholerae, ETEC, EAggEC, EPEC, EHEC.
What is the second clinical syndrome?
Fever, WBC in stool
Campylobacter, shigella, non typhoid all salmonella, EIEC
What is the 3rd clinical syndrome?
Fever, WBC in stool (mononuclear)
Typhoidal salmonella, enteropathogenic yersinia, brucella
Incubation and duration for campylobacter?
1-10 days incubation
2-20 days duration
Incubation and duration for E. coli?
1-5 days incubation
1-4 days duration
Incubation and duration for shigella?
12-96 hours incubation
5-7 days duration
Small infective dose, outbreaks
Incubation and duration for non typhoidal salmonella?
8-48 hours incubation
4-7 days duration
Rare cause of systemic disease
Incubation and duration for vibrio parahaemolyticus?
24-72 hours incubation
Incubation and duration for cholera?
1-5 days incubation
Incubation and duration for b cereus?
1-6 hours incubation
Less than1 day duration
Heat stable emetic toxin (rice)
Incubation and duration for staph aureus?
2-7 hours duration
Less than one day duration
Mechanism for cholera- secretory diarrhoea
Toxins bind to units
Opening up of chloride channels at the apical membrane of enterocytes by cAMP
Effluent of chloride into the lumen with loss of water and electrolytes
Mechanism of disease with secretory diarrhoea- super antigen
Antigen binds 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
Who tends to get an exudative or inflammatory response?
What happens with interstitial inflammation/enteric?
Immunocompetent, no septic shock.
Facts about s aureus leading to food poisoning?
1/3 chronic carriers, 1/3 transient
Spread by skin lesion on food handlers
Catalase, coagulase, gram positive coccus
Appears in tetrads, clusters on gram stain
What is the mechanism of s aureus?
Produces an enterotoxin, an exotoxin that can act as a super antigen, releasing IL 1 and 2.
Causing prominent vomiting and watery non bloody diarrhoea
No heat inactivation
Mechanism for b cereus?
Gram positive rod, spore forming
Spores germinate in reheated fried rice
Heat stable emetic toxin
Heat labile diarrhoeal toxin
Watery non bloody diarrhoea
Rare cause of bacteraemia
Can cause cerebral abcess
Facts about clostridium botulinum?
Gram positive anaerobes
Source is canned or vacuumed food
Ingestion of preformed toxin, inactivated by Heat
Blocks ACH release from peripheral nerve synapses
Tx is with antitoxin
Mechanism for clostridium pefringens?
Affects normal flora of colon but not small bowel, where super antigen acts
8-16 hours incubation
Vomiting 24 hours
Pseudo membranous colitis
3% population 30% hospital
Abx related colitis mainly, cephalosporin, Citroen and clindamycin
Monitor albumin, renal function and white cells
Tx with oral metro, vanco.
Outbreaks of febrile gastroenteritis
Pregnant ladies, perinatal infection
B haemolytic, aesculin positive with tumbling motility
Refridgerated food, grows at 4 degrees Celsius
Watery diarrhoea, cramps, headache, fever, little vomiting
Tx with ampicillin, ceftriaxone, cotrimoxazole
What are enterobacteriae?
Facultative anaerobes, glucose/lactose fermenters, oxidase negative
Food/water contaminated with human faeces
Enterotoxins- Heat labile stimulates adenyl cyclase, and cAMP
Heat stable stimulates guanylate cyclase
Act on jejenun and ileum NOT colon
What is ETEC?
What is EPEC?
What is EIEC?
What is EHEC?
Shiga like verocytotoxin causes HUS
Why are infections underreported?
Most are self limiting, under 24 hours, patients do not seek healthcare
What are salmonellae?
They are non lactose fermenters, they produce hydrogen disulphide
They produce antigens
What are the antigens from salmonellae?
Cell wall O(groups a-I)
Capsular Vi (virulence and antiphagocytic)
What are the 3 salmonellae species?
What does s enteritidis cause?
Enterocolitis, poultry, eggs, meat
Invasion of epi and sub epithelial tissue of small and large bowel
Bacteraemia is infrequent
Self limited, non bloody diarrhoea
Give cipro after 3-5 days
What does s typhi cause?
Enteric fever, South East Asia, humans
Multiples in payers patches
Slow, fever, constipation
Anaemia, leucopenia, bradycardia, haemorrhage
Blood culture positive (abcess.mycotic aneurysm)
Treat with ceftriaxone
What is shigellae?
Gram negative anaerobes, non motile
What are the shigellae antigens?
Cell wall O
Polysaccharide groups a-d
What are the 3 shigellae species?
S sonnei, s dysenteriae, s flexneri (msm, faecal)
The most effective enteric pathogen low ID 50
No animal reservoir
No carrier state
What does shigella cause?
Dysentery, invading cells of mucosa of distal ileum and colon
Producing enterotoxin (shigatoxin)
Avoid abx (ciprofloxacin to prevent onward spread)
What are vibrios?
Gram negative rod shaped, late lactose fermenters, oxidase positive
What is vibrio cholera?
O1 group causes epidemics
Non O1 group is sporadic or non pathogens
Transmitted by contamination of water and food from human faeces (shellfish, oysters and shrimp)
How does v cholera work?
Colonisation of the small bowel, secretion of enterotoxin with A and B subunit, causing persistent stimulation of adenylate cyclise
Massive diarrhoea without any white cells
How does vibrio parahaemolyticus work?
Ingestion of raw or undercooked seafood
Major cause of diarrhoea in Japan, or cruising
Self limiting for 3 days
Grows in salty conditions
How does vibrio vulnificus work?
Causes cellulitis in shellfish handlers, waterborne.
Can cause fatal septicaemia if immunosuppressive (HIV)
Treat with doxycycline
What is campylobacter?
Gram negative, microaerophilic
Grows at 42 degrees
Motile, oxidative positive
Self limiting but symptoms can last for 20 days
Lives in poultry gut
Only treat with immunocomprimise does with macrolide
How is campylobacter transmitted?
Contaminated food and water with animal faeces (poultry, meat, birds pecking on milk)
Enterotoxin, watery diarrhoea
Fever, abdo pain
Not sure if it invades blood (f one does)
Treat with erythromycin or cipro in first 4-5days
What syndrome can campylobacter cause?
What is yersinia enterocolitica?
Gram negative rod shaped
Non lactose fermenters, prefers cold 4 degrees
Transmitted via food contaminated with domestic animal poo
Can cause enterocolitis, mesenteric adenitis, assoc reactive arthritis, reiters
What is entamoeba histolytica?
Motile trophozoite in diarrhoea
Non motile in non diarrhoeal
Killed by boiling, removed by water filter
4 nuclei, no animal reservoir
How does e histolytica work?
Ingestion of cysts, trophies in ileum, colonise caecum, causes flask shaped ulcer
Dysentery and flatulence
Chronic weight loss, plus diarrhoea
How would you diagnose e histolytica?
Stool microbiology (wet mount, iodine, trichrome)
Serology in invasive disease
How do you treat e histolytica?
Metro plus paromomycin in luminal disease
What is giardia?
2 nuclei, 4 flagella, suction disk
How is giardia passed?
Ingestion of cyst from faecally contaminate water, food
Excystation at the duodenum
No invasion but malabsorption of protein or fat
Travellers hikers, day care, mental hospital people can't look after themselves msm.
What are the symptoms of giardia?
Foul smelling non bloody diarrhoea stool floats
How can you diagnose giardia?
String test- capsule with string into stomach
Treat with metro
What is cryptosporidium parvum?
Protozoa, infects the jejenum
Severe diarrhoea in the immunocompromised
Oocysts seen in stool, modified by kinyoun acid fast stain
Treatment- reconstitution of immune system
Picked up from swimming
What is norovirus?
Low ID (18-1000 viral particles)
Resilient up to 60 degrees celcius
No long term immunity
G2.4 is the currently predominant strain
Vomiting and diarrhoea
What is rotavirus?
Wheel like virus, dsRNA
Replicates in mucosa of small intestine
Can get watery diarrhoea by stimulation of enteric nervous system
Who gets rotavirus?
Age 6 kids most have it
Exposure to natural infection twice confers lifelong immunity
What can adenovirus cause?
Types 40, 41 cause non bloody diarrhoea, usually less than 2 years of age
Any type in immunocompromised
How do you diagnose adenovirus?
Stool em, antigen detection, PCR
What are the targets for prevention promotion?
Breast feeding, improved weening practice
Clean water for drinking
Safe disposal of stools of young children
Precautions when travelling
Public health notification
What is the cholera vaccine?
Inactivated whole cell, contains serogroups O1 and O139
Plus beta unit of toxin
Live is not recommend
What about campylobacter vaccine?
One available for military, infant and travellers
Candidate vaccines exist only for high risk
Are there any ETEC vaccines?
Inactivated and live vaccines in trials
Is there a salmonella vaccine?
Yes, vi capsular ps (IM) and oral live
What are the rotavirus vaccines?
Rotarix- live attenuated human strain, 2 oral doses
Rotateq- pentavalent, 3 oral doses, one bovine, 4 human strains
6-12 weeks , UK don't get it really