Microbiology - Gastrointestinal Infections Flashcards
Risk Factors
Lack of clean water, poor sanitation Overcrowding Poor hygiene Poor food preparation/storgae Seasonal factors
Host Factors
Age (very young/elderly) Decreased gastric acid secretion Decreased gut motility Influence of colonic microflora Intestinal immunity
Define Diarrhoea
Three or more loose stools in 24 hours
Define Source/Reservoir of Infection
Original source of infection
E.g. animal gut, human gut
Define Vehicle of Infection
Means by which the infection is transmitted from one person to another
E.g. contaminated food/water
Campylobacter - Classification
Curved gram negative bacillus
Campylobacter - Incubation Period
3-10 days
DAYS - WEEK
Campylobacter - Mechanism of Action
Causes inflammation of colon and rectum = bloody diarrhoea
Can invade bloodstream
Campylobacter - Source and Vehicle of Infection
Farm animals
Undercooked poultry, water, unpasteurised milk
Campylobacter - Symptoms
Abdo pain
Diarrhoea +/- blood
Campylobacter - Management
Usually self limiting
Systemic illness = erythromycin or ciprofloxacin for 5 days
Salmonella enterica - Incubation Period
12-48 hours
HOURS - DAY
Salmonella enterica - Mechanism of Action
Causes inflammation of ileum and colon
Multiply in gut and cause mucosal damage, decreased fluid absorption and increased fluid excretion
Can invade bloodstream
Salmonella enterica - Source and Vehicle of Infection
Farm animals
Undercooked poultry
Less common since immunisation of poultry against salmonella
Salmonella enterica - Symptoms
Abdo pain
Diarrhoea (occasionally bloody)
Vomiting
Salmonella enterica - Management
Usually self limiting
Systemic illness = ciprofloxacin for 5 days
Shigella - Incubation Period
1-9 days
DAYS - WEEK
Shigella - Mechanism of Action
Invades intestinal mucosa causing severe inflammation
Does not invade bloodstream
Pus cells and blood seen in stools
Shigella - Source and Vehicle of Infection
Human only
Associated with schools and nurseries
Shigella - Symptoms
Abdo pain
Diarrhoea (occasionally bloody)
Shigella - Management
Usually self limiting
S sonnei = only symptomatic treatment
Other species = ciprofloxacin
E coli O157 - Mechanism of Action
Produces a toxin that damages red cells and the kidney
Leads to haemolytic-uraemic syndrome
E coli O157 - Source and Vehicle of Infection
Gut flora in cattle Beef contaminated at slaughter Nursery school visits to farms Untreated water supplies Person to person causes secondary cases
E coli O157 - Symptoms
Abdo pain
Commonly bloody diarrhoea
E coli O157 - Management
Symptomatic and supportive treatment only
Antibiotics contraindicated
Check for HUS after 1 week
Clinical Presentation of HUS
Abdo pain Fever Pallor Petechiae (skin haemorrhages) Oliguria (decreased urine) Bloody diarrhoea Mostly in under 16s Peak presentation 7-10 days after diarrhoea onset
HUS Blood Tests
High white cells Low platelets Low HB Red cell fragments Lactate dehydrogenase increased
Salmonella, Shigella and E coli O157 - Classification
Gram negative bacilli
Further classify through serology
Salmonella typhi/paratyphi - Background Info
Cause tyhpoid/paratyphoid fever
Seen in UK when imported from abroad
Salmonella typhi/paratyphi - Incubation Period
14-21 days
WEEKS
Salmonella typhi/paratyphi - Mechanism of Action
Organism invades from gut lumen to lymphatics, blood stream, reticuloendothelial system and gall bladder
Some people become chronic carriers (gallbladder)
Salmonella typhi/paratyphi - Source and Vehicle of Infection
Human only
Person to person or contaminated water, food and poor sanitation
Salmonella typhi/paratyphi - Symptoms
Initially systemic headache/flu like symptoms
Fever
Abdo rash (rose spots)
3 weeks later, diarrhoea
Salmonella typhi/paratyphi - Management
Antibiotics needed
Depends on sensitivities
Ciprofloxacin resistance common in developing countries
Cholera - Causative Organism
Vibrio cholerae
Small curved gram negative bacillus
Cholera - Incubation Period
1-9 days
DAYS - WEEK
Cholera - Mechanism of Action
Organism produces exotoxin that causes active outpouring of fluid from small intestine cells
Cholera - Source and Vehicle of Infection
Human only
Person to person or contaminated water and poor sanitation
Outbreaks common in “disaster” or war situations
Cholera - Symptoms
Watery diarrhoea (rice water stools) Rapid dehydration
Cholera - Management
Fluid and electrolyte replacement
No antibiotics
GI Infections Associated with Ingestion of Pre-formed Toxin
Staph aureus
Clostridium perfringens
Bacillus cereus
Generally have much shorter incubation periods
Staphylococcus aureus
Some strains produce enterotoxin
Generally spread via contaminated food
Absorbs quickly, acts directly on vagus nerve and vomiting centre, vomiting within 1-2 hours
Clostridium perfringens
Part of normal gut flora
Spores survive cooking, turn into vegetative organisms, some strains produce enterotoxin
Associated with poorly stored food
Bacillus cereus
Exotoxin ingested as pre-formed toxin in food or organism multiplies in intestine, producing toxin that is absorbed from gut
Spores survive cooking, turn into vegetative organisms which produce toxin
Associated with poorly stored reheated rice
Cryptosporidium
Single celled parasite
Cryptosporidium - Mechanism of Action
Cysts ingested which hatch and invade small intestine cells
Cryptosporidium - Source and Vehicle of Infection
Domestic animals, especially calves
Person to person
Outbreaks associated with contaminated water and swimming pools (resistant to chlorine)
Cryptosporidium - Symptoms
Diarrhoea
Severe in HIV patients
Cryptosporidium - Management
Symptomatic treatment only
Giardia lamblia
Single celled parasite
Probably under diagnosed in Scotland
Giardia lamblia - Mechanism of Action
Cysts ingested which hatch and invade upper small intestine cells
Giardia lamblia - Source and Vehicle of Infection
Human only
Possible person to person
Outbreaks associated with contaminated water
Giardia lamblia - Symptoms
Diarrhoea Malabsorption syndrome Anorexia Abdo pain Flatulence
Giardia lamblia - Management
Oral metronidazole
Enterobius vermicularis - Pathogenesis
Ingested ova
Hatch in intestine and live in caecum & colon
Adult females lay ova on perianal skin at night
Ova cause perianal itch
Child scratches then puts fingers into mouth
Enterobius vermicularis - Source and Vehicle of Infection
Human only
Person to person
Poor hygiene
Enterobius vermicularis - Symptoms
Perianal itch
Worms in stool
Enterobius vermicularis - Management
Oral mebendazole
Treat all family at once
C.diff - Mechanism of Action
Organism produces two toxins: A (enterotoxin) and B (cytotoxin)
C.diff - Source and Vehicle of Infection
Part of normal gut flora
Antibiotics kill normal gut flora, but C.diff survives due to spores
Patient to patient spread
C.diff - Symptoms
Diarrhoea, sometimes bloody
Abdo pain
Severe cases = pseudomembranous colitis or bowel perforation
C.diff - Management
Less severe = oral metronidazole
Severe = oral vancomycin
C.diff - Prevention
Stewardship = Narrow spectrum antibiotics where possible and avoidance of 4 Cs
Isolation of patients
Hand washing
Cleaning of environment
C.diff - Classification
Gram positive, spore bearing, bacillus
C.diff - Lab Diagnosis
Screening test for positive organism (GDH)
Toxin test if GDH positive
Culture is strain needs to be typed
Screening -ve = -ve
Screening +ve, toxin +ve = +ve
Screening +ve, toxin -ve = indeterminate
Indeterminate = reassess and repeat. If still indeterminate, clinical judgement (smells of horse dung)
Rotavirus - Typical Presentation
Commonest in children
Rotavirus - Vehicle of Infection
Person to person spread
Direct or indirect
Low infective dose
Survives in the environment
Rotavirus - Symptoms
Mild to severe diarrhoea
No blood
Dehydration
Children may develop post infective malabsorption
Rotavirus - Treatment
Self limiting (~ 1 week) Oral rehydration where possible
Rotavirus - Diagnosis
PCR test on faeces
Rotavirus - Prevention
Live attenuated vaccine
2 doses at 2 and 3 months
Not given to children over 24 weeks because of increased risk of intussusception
Norovirus - Route of Spread
Faecal/oral droplets Person to person Contaminated food/water High environmental survival Low infective dose
Norovirus - Incubation Period
Often
Norovirus - Symptoms
Sudden onset explosive D&V
Lasts 2-4 days
Norovirus - Diagnosis
Faeces specimen or vomit swab for PCR
Norovirus - Treatment
Rehydration
Hospital Control of Infectious Diarrhoea
Single room with own toilet/commode
Cohort nursing bays during outbreaks
Wards closed to new admissions
Increased ward cleaning/disinfection
Doctors and Diarrhoea
Infectious diarrhoea, stay off work until 48 hours after symptoms have stooped
Inform line manager and Occ Health
