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GI > Microbiology - Gastrointestinal Infections > Flashcards

Microbiology - Gastrointestinal Infections Flashcards

1
Q

Risk Factors

A 
Lack of clean water, poor sanitation
Overcrowding
Poor hygiene 
Poor food preparation/storgae
Seasonal factors
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2
Q

Host Factors

A 
Age (very young/elderly)
Decreased gastric acid secretion 
Decreased gut motility
Influence of colonic microflora
Intestinal immunity
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3
Q

Define Diarrhoea

A

Three or more loose stools in 24 hours

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4
Q

Define Source/Reservoir of Infection

A

Original source of infection

E.g. animal gut, human gut

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5
Q

Define Vehicle of Infection

A

Means by which the infection is transmitted from one person to another
E.g. contaminated food/water

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6
Q

Campylobacter - Classification

A

Curved gram negative bacillus

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7
Q

Campylobacter - Incubation Period

A

3-10 days

DAYS - WEEK

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8
Q

Campylobacter - Mechanism of Action

A

Causes inflammation of colon and rectum = bloody diarrhoea

Can invade bloodstream

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9
Q

Campylobacter - Source and Vehicle of Infection

A

Farm animals

Undercooked poultry, water, unpasteurised milk

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10
Q

Campylobacter - Symptoms

A

Abdo pain

Diarrhoea +/- blood

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11
Q

Campylobacter - Management

A

Usually self limiting

Systemic illness = erythromycin or ciprofloxacin for 5 days

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12
Q

Salmonella enterica - Incubation Period

A

12-48 hours

HOURS - DAY

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13
Q

Salmonella enterica - Mechanism of Action

A

Causes inflammation of ileum and colon
Multiply in gut and cause mucosal damage, decreased fluid absorption and increased fluid excretion
Can invade bloodstream

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14
Q

Salmonella enterica - Source and Vehicle of Infection

A

Farm animals
Undercooked poultry
Less common since immunisation of poultry against salmonella

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15
Q

Salmonella enterica - Symptoms

A

Abdo pain
Diarrhoea (occasionally bloody)
Vomiting

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16
Q

Salmonella enterica - Management

A

Usually self limiting

Systemic illness = ciprofloxacin for 5 days

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17
Q

Shigella - Incubation Period

A

1-9 days

DAYS - WEEK

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18
Q

Shigella - Mechanism of Action

A

Invades intestinal mucosa causing severe inflammation
Does not invade bloodstream
Pus cells and blood seen in stools

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19
Q

Shigella - Source and Vehicle of Infection

A

Human only

Associated with schools and nurseries

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20
Q

Shigella - Symptoms

A

Abdo pain

Diarrhoea (occasionally bloody)

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21
Q

Shigella - Management

A

Usually self limiting
S sonnei = only symptomatic treatment
Other species = ciprofloxacin

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22
Q

E coli O157 - Mechanism of Action

A

Produces a toxin that damages red cells and the kidney

Leads to haemolytic-uraemic syndrome

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23
Q

E coli O157 - Source and Vehicle of Infection

A 
Gut flora in cattle
Beef contaminated at slaughter 
Nursery school visits to farms
Untreated water supplies 
Person to person causes secondary cases
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24
Q

E coli O157 - Symptoms

A

Abdo pain

Commonly bloody diarrhoea

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25
Q

E coli O157 - Management

A

Symptomatic and supportive treatment only
Antibiotics contraindicated
Check for HUS after 1 week

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26
Q

Clinical Presentation of HUS

A 
Abdo pain
Fever
Pallor 
Petechiae (skin haemorrhages)
Oliguria (decreased urine)
Bloody diarrhoea 
Mostly in under 16s
Peak presentation 7-10 days after diarrhoea onset
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27
Q

HUS Blood Tests

A 
High white cells
Low platelets 
Low HB
Red cell fragments
Lactate dehydrogenase increased
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28
Q

Salmonella, Shigella and E coli O157 - Classification

A

Gram negative bacilli

Further classify through serology

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29
Q

Salmonella typhi/paratyphi - Background Info

A

Cause tyhpoid/paratyphoid fever

Seen in UK when imported from abroad

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30
Q

Salmonella typhi/paratyphi - Incubation Period

A

14-21 days

WEEKS

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31
Q

Salmonella typhi/paratyphi - Mechanism of Action

A

Organism invades from gut lumen to lymphatics, blood stream, reticuloendothelial system and gall bladder
Some people become chronic carriers (gallbladder)

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32
Q

Salmonella typhi/paratyphi - Source and Vehicle of Infection

A

Human only

Person to person or contaminated water, food and poor sanitation

33
Q

Salmonella typhi/paratyphi - Symptoms

A

Initially systemic headache/flu like symptoms
Fever
Abdo rash (rose spots)
3 weeks later, diarrhoea

34
Q

Salmonella typhi/paratyphi - Management

A

Antibiotics needed
Depends on sensitivities
Ciprofloxacin resistance common in developing countries

35
Q

Cholera - Causative Organism

A

Vibrio cholerae

Small curved gram negative bacillus

36
Q

Cholera - Incubation Period

A

1-9 days

DAYS - WEEK

37
Q

Cholera - Mechanism of Action

A

Organism produces exotoxin that causes active outpouring of fluid from small intestine cells

38
Q

Cholera - Source and Vehicle of Infection

A

Human only
Person to person or contaminated water and poor sanitation
Outbreaks common in “disaster” or war situations

39
Q

Cholera - Symptoms

A 
Watery diarrhoea (rice water stools)
Rapid dehydration
40
Q

Cholera - Management

A

Fluid and electrolyte replacement

No antibiotics

41
Q

GI Infections Associated with Ingestion of Pre-formed Toxin

A

Staph aureus
Clostridium perfringens
Bacillus cereus
Generally have much shorter incubation periods

42
Q

Staphylococcus aureus

A

Some strains produce enterotoxin
Generally spread via contaminated food
Absorbs quickly, acts directly on vagus nerve and vomiting centre, vomiting within 1-2 hours

43
Q

Clostridium perfringens

A

Part of normal gut flora
Spores survive cooking, turn into vegetative organisms, some strains produce enterotoxin
Associated with poorly stored food

44
Q

Bacillus cereus

A

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

45
Q

Cryptosporidium

A

Single celled parasite

46
Q

Cryptosporidium - Mechanism of Action

A

Cysts ingested which hatch and invade small intestine cells

47
Q

Cryptosporidium - Source and Vehicle of Infection

A

Domestic animals, especially calves
Person to person
Outbreaks associated with contaminated water and swimming pools (resistant to chlorine)

48
Q

Cryptosporidium - Symptoms

A

Diarrhoea

Severe in HIV patients

49
Q

Cryptosporidium - Management

A

Symptomatic treatment only

50
Q

Giardia lamblia

A

Single celled parasite

Probably under diagnosed in Scotland

51
Q

Giardia lamblia - Mechanism of Action

A

Cysts ingested which hatch and invade upper small intestine cells

52
Q

Giardia lamblia - Source and Vehicle of Infection

A

Human only
Possible person to person
Outbreaks associated with contaminated water

53
Q

Giardia lamblia - Symptoms

A 
Diarrhoea 
Malabsorption syndrome 
Anorexia 
Abdo pain 
Flatulence
54
Q

Giardia lamblia - Management

A

Oral metronidazole

55
Q

Enterobius vermicularis - Pathogenesis

A

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

56
Q

Enterobius vermicularis - Source and Vehicle of Infection

A

Human only
Person to person
Poor hygiene

57
Q

Enterobius vermicularis - Symptoms

A

Perianal itch

Worms in stool

58
Q

Enterobius vermicularis - Management

A

Oral mebendazole

Treat all family at once

59
Q

C.diff - Mechanism of Action

A

Organism produces two toxins: A (enterotoxin) and B (cytotoxin)

60
Q

C.diff - Source and Vehicle of Infection

A

Part of normal gut flora
Antibiotics kill normal gut flora, but C.diff survives due to spores
Patient to patient spread

61
Q

C.diff - Symptoms

A

Diarrhoea, sometimes bloody
Abdo pain
Severe cases = pseudomembranous colitis or bowel perforation

62
Q

C.diff - Management

A

Less severe = oral metronidazole

Severe = oral vancomycin

63
Q

C.diff - Prevention

A

Stewardship = Narrow spectrum antibiotics where possible and avoidance of 4 Cs
Isolation of patients
Hand washing
Cleaning of environment

64
Q

C.diff - Classification

A

Gram positive, spore bearing, bacillus

65
Q

C.diff - Lab Diagnosis

A

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)

66
Q

Rotavirus - Typical Presentation

A

Commonest in children

67
Q

Rotavirus - Vehicle of Infection

A

Person to person spread
Direct or indirect
Low infective dose
Survives in the environment

68
Q

Rotavirus - Symptoms

A

Mild to severe diarrhoea
No blood
Dehydration
Children may develop post infective malabsorption

69
Q

Rotavirus - Treatment

A 
Self limiting (~ 1 week)
Oral rehydration where possible
70
Q

Rotavirus - Diagnosis

A

PCR test on faeces

71
Q

Rotavirus - Prevention

A

Live attenuated vaccine
2 doses at 2 and 3 months
Not given to children over 24 weeks because of increased risk of intussusception

72
Q

Norovirus - Route of Spread

A 
Faecal/oral droplets
Person to person 
Contaminated food/water 
High environmental survival 
Low infective dose
73
Q

Norovirus - Incubation Period

A

Often

74
Q

Norovirus - Symptoms

A

Sudden onset explosive D&V

Lasts 2-4 days

75
Q

Norovirus - Diagnosis

A

Faeces specimen or vomit swab for PCR

76
Q

Norovirus - Treatment

A

Rehydration

77
Q

Hospital Control of Infectious Diarrhoea

A

Single room with own toilet/commode
Cohort nursing bays during outbreaks
Wards closed to new admissions
Increased ward cleaning/disinfection

78
Q

Doctors and Diarrhoea

A

Infectious diarrhoea, stay off work until 48 hours after symptoms have stooped
Inform line manager and Occ Health

GI (24 decks)

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