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GI Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Duration of GI symptoms

A
  • acute: < 14 days
  • persistant: < 30 days
  • chronic: > 30 days
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2
Q

GI anatomic considerations

A
  • esophagus to stomach to small intestine to large intestine
  • pH of stomach can withstand most bacteria
  • peristalsis of small intestine inhibits adherence
  • colon flora and IgA compete with pathogens
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3
Q

GI risk factors

A
  • number of ingested organisms
  • achlorhydia
  • reduction in normal flora due to antibiotics
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4
Q

Traveler’s diarrhea

A

Enterotoxigenic E. coli

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5
Q

Parasitic infections

A

Giardia, Entamoeba

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6
Q

Antibiotic-associated diarrhea

A

C. difficile

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7
Q

Practical diagnosis

A
  • History (food ingestion, travel, activities)
  • Duration of illness
  • Medications
  • Underlying conditions
  • Physical exam (state of hydration, exam of abdomen)
  • Laboratory studies
  • Fecal exam
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8
Q

Direct fecal smear

A
  • Gram stain of smear
  • WBC’s indicate invasion, not toxin
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9
Q

Enterotoxin-mediated diarrhea

A
  • rapid onset indicates preformed toxin
  • lack of fever
  • absence of blood or pus
  • large number of watery stools (> 20/day)
  • Enterotoxigenic E. coli, cholera, S. aureus, C. perfringens, Bacillus cereus, viral or parasitic
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10
Q

Diarrhea mediated by invasion of bowel mucosal surface

A
  • fecal leukocytes, RBC’s, fever
  • Salmonella, Campy, Shigella, E. coli, Entamoeba
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11
Q

Diarrhea mediated by invasion of full thickness of bowel with lymphatic spread

A
  • S. typhi, Y. enterocolitica
  • presents with constipation
  • fecal leukocytes and RBC’s
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12
Q

Common viral pathogens

A

Norovirus, Rotavirus, Adenovirus,? Some Enterovirus

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13
Q

Common bacterial pathogens

A

Salmonella, Shigella, Campylobacter. E coli, Yersinia, Clostridium difficile

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14
Q

Common parasitic pathogens

A

Giardia intestinalis, E. histolytica, Cryptosporidium, Cyclospora, Microsporidia

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15
Q

common protozoa

A

Giardia, Cryptosporidium, Entamoeba

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16
Q

common toxins associated with GI

A

Staphylococcal, Bacillus cereus, Cl botulinum, Cl perfringens, Scrombotoxin

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17
Q
  • most common cause of diarrheal illness worldwide
  • microaerophilic, Campy BAP, 42C
  • seagull wing appearance, darting motility
  • oxidase +, catalase +
A

Campylobacter jejuni

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18
Q
  • contaminated meat, eggs
  • symptoms 6-8 hours after ingestion
  • usually self-limiting
  • indole -, K/A H2S +, oxidase -
  • enteric fever
  • high inoculum required
A

Salmonella typhi

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19
Q

how many salmonella organisms need to be ingested for infection?

A

need around 1000 organisms per g of food to get infected

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20
Q
  • dysenteriae, flexneri, boydii, sonnei
  • sonnei is most common in US
  • non-motile, oxidase -
  • causes dynsentery
  • low inoculum required
A

Shigella

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21
Q
  • infantile diarrhea
  • adhesive, mucus in stool (no blood)
A

Enteropathogenic E. coli

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22
Q
  • Traveler’s diarrhea
  • due to poor sanitation
  • requires large inoculum
  • releases toxins
A

Enterotoxigenic E. coli

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23
Q
  • dysentery with direction invasion/destruction of mucosa
  • similar to Shigella, but higher inoculum
  • watery diarrhea with blood, mucus and WBCs
A

Enteroinvasive E. coli

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24
Q
  • rice-water stool
  • large loss of electrolytes
  • associated with epidemics
  • catalase +, oxidase +
  • toxin produced
  • yellow on TCBS
A

Vibrio cholera

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25
Q
  • Summer diarrhea in Japan, associated with seafood
  • diarrhea and cramping
  • green on TCBS
A

Vibrio parahaemolyticus

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26
Q
  • “lactose positive” species
  • raw or undercooked seafood, wounds
  • green on TCBS
A

Vibrio vulnificus

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27
Q
  • grows at 4C, can go septic
  • meat, unpasteurized milk, dairy products
  • CIN agar (target growth)
  • K/A, ODC +, non-motile
  • self-limiting, possible invasion of mesenteric lymph nodes
  • sometimes mistaken for appendicitis
A

Yersinia enterocolitica

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28
Q
  • sometimes normally in intestines
  • antibiotic-associated diarrhea
  • pseudomembranous colitis
  • mild to severe disease
A

Clostridium difficile

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29
Q
  • deli meat
  • grows at cold temps
  • CAMP +, catalase +, tumbling motility
  • premature labor, spontaneous abortion
A

Listeria monocytogenes

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30
Q
  • peptic ulcers
  • stomach cancer
  • urease +, Christensen’s urea medium, urea breath test
  • cinaedi and fennelliae associated with diarrhea
A

Helicobacter pylori

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31
Q

STD’s causing GI infections

A
  • cause proctitis with lose stools and pain on defecation
  • N. gonorrhoeae, Chlamydia, Treponema
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32
Q

Toxic agents of Food Poisoning (chemical)

A
  • scombroid: flushing, headache, crampy abdominal, tissue of fish
  • Ciguatera: red tide toxin buildup in fish, diarrhea, weakness, abdominal pain
  • Tetrodotoxin: puffer fish toxin (death in 50%)
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33
Q

Preformed toxin from food borne disease?

A

S.aureus, B.cereus,Cl botulinum, scrombotoxin and paralytic shellfish poisoning

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34
Q

Toxin production in vivo from food borne disease?

A

C perfringens, B.cereus, Enterotoxigenic E.coli

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35
Q

Tissue invasion in food borne disease?

A

C.jejuni, Salmonella, Shigella, VTEC

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36
Q

when are the peaks of food borne disease during the year?

A

Peaks at Christmas (eat too much) and summer (BBQ)

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37
Q

HE plate

A
  • Salmonella shows H2S (black colonies)
  • Shigella has no H2S
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38
Q

SMAC

A

E. coli O157:H7 doesn’t ferment sorbitol

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39
Q

Campy agar

A

selective for Campylobacter jejuni

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40
Q

CIN agar (cefsulodin- Igrasan-novobiocin)

A

selective for Yersinia enterocolitica (target/bulls-eye growth)

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41
Q

TCBS agar

A
  • Vibrio cholera and alginolyticus utilize sucrose (turn yellow)
  • Vibrio vulnificus and parahaemolyticus don’t utilize sucrose
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42
Q

CCFA agar

A

selective for C. difficile (pale yellow colonies - fluoresce bright yellow)

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43
Q

Diarrhea treatment and prevention

A
  • replenish electrolytes (IV fluids if necessary)
  • antidiarrheal medications (not for invasive diarrhea)
  • antibiotics to treat infection
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44
Q

incubation period of norovirus?

A

Usually 24 to 48 hours

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45
Q

common clinical features?

A

Vomiting, diarrhoea, fever

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46
Q

diagnosis?

A

EM, PCR

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47
Q

how is norovirus transmitted?

A

Person to person by the faecal oral route

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48
Q

how can vomiting transmitted the virus?

A

risk of infection from aerosols of projectile vomit.

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49
Q

how does norovirus contaminate the environment?

A

especially of toilets; gloves should be used by cleaners. Contaminated food and water, especially bivalve molluscs.

50
Q

how many organisms does it take to infect a person?

A

2-3

51
Q

what is the incubation period of rotavirus?

A

Approximately 48 hours.

52
Q

what are the clinical features?

A

Diarrhoea, vomiting.

53
Q

diagnosis?

A

ELISA, EM

54
Q

transmission?

A

Person to person by faecal oral route by environmental contamination

55
Q

significant characteristic of the viruses?

A

Enveloped viruses

56
Q

whats the incubation period of a E coli O157 infection?

A

1 to 10 days.

57
Q

what does a diagnosis require?

A

Culture/serotyping/ toxin detection (serology)

58
Q

what is the Reservoir of e coli O157?

A

The gastrointestinal tract of cattle and possibly other domesticated animals

59
Q

how is the infection transmitted?

A

Contaminated foodstuffs - beef and beef products (for example, undercooked beefburgers), milk, and vegetables have been associated with cases or outbreaks.
Contact with infected animals, particularly on farms or in animal sanctuaries.

60
Q

can it be spread from person to person?

A

Person to person spread can occur by direct contact (faecal oral), particularly in households, nurseries, and infant schools.

61
Q

what complications are associated with infection?

A

HUS, Haemorrhagic colitis

62
Q

what is the incubation period of Shigella species infections?

A

1 - 7 days

63
Q

how is a infection diagnosed?

A

culture

64
Q

how is it transmitted?

A

Faecal oral from cases with diarrhoea, in households, and institutions, mainly those containing young children. Occasionally spread by food and water.

65
Q

which species is endemic in UK and wales?

A

S. sonnei
causing mild illness

66
Q

which species originate outside of UK?

A

S. boydii and S. dysenteriae, and most S. flexneri

67
Q

how do they present clinically?

A

as dysentery (diarrhoea with blood, mucus, and pus).

68
Q

what is S. dysenteriae may be associated with?

A

serious disease, including toxic megacolon and the haemolytic uraemic syndrome

69
Q

what is the incubation period of Cryptosporidium​?

A

2-5 days

70
Q

what are the reservoirs of cryptosporidium?

A

Gastrointestinal tract of man and animals, particularly farm and other domesticated animals. Water contaminated with faeces.

71
Q

what are the two main genotypes of transmission?

A

parvum and hominis

72
Q

what is the parvum transmission?

A

Contact with infected animals. Outbreaks have been associated with public water supplies and contaminated food.
Seasonal outbreaks are associated with farm visits to feed and handle lambs.

73
Q

what is the hominis transmission?

A

Person to person spread, particularly in households and nurseries. Infection through swimming pools has been reported.

74
Q

what is the incubation period for Giardia lamblia infection?

A

5-25 days

75
Q

how is the infection transmitted?

A

Person to person. Foodborne transmission is rare.
Faecal oral in young children. Waterborne. Spread within families is common

76
Q

Gram positive, anaerobic bacillus

A

Clostridium difficile​

77
Q

what is the main transmission mode of clostridium difficile?

A

Subterminal spores

78
Q

how are the spores spread?

A

Patient to patient
Spread via hands of HCWs
Spread via environment
Transmission from asymptomatic patients unlikely

79
Q

how do the spores survive in any environment?

A

resistant to heat, air and drying

80
Q

how many toxins do clostridium difficile produce?

A

two, toxin A and B

81
Q

toxin A?

A

loss of fluid from gut mucosa

82
Q

toxin B?

A

potent cytopathic toxin ​

83
Q

where does the infection affect?

A

Predominantly affects the colon​

84
Q

how does it present clinically?

A

Abdominal pain, explosive, watery, foul smelling diarrhoea, fever​

Variable severity​​

85
Q

what complication is common?

A

Recurrence after successful treatment is common​

May have long period of excretion

86
Q

when do you test for infection?

A

All adult inpatients with diarrhoea​

Other risk groups​
- children

87
Q

what used to be the gold standard for diagnosis?

A

Demonstration of toxin in stool by cell culture – overnight incubation required

88
Q

what other diagnostic tests are available now?

A

“sniff” test ​

Commercial ELISA (sensitivity 75-95%)​

culture/ribotyping for epidemiological studies​

Glutamate dehydrogenase detection + toxin detection

89
Q

what must be remembered when using the diagnostic tests?

A

do not rely on one false negative

90
Q

what groups of people are susceptible?

A

old and young
people with antibiotic treatment

91
Q

what Underlying diseases could help infection?

A

Surgery due to prophylactic antibiotics given before surgery

Cancer patients coz immunosurpressed

chronic renal disease

92
Q

how can infection be prevented?

A

Control of antibiotic usage
Handwashing
Cleaning/disinfection/sterilisation of equipment
Environmental cleaning

93
Q

how can outbreaks be controlled?

A

Isolation of cases and cohort nursing
Antibiotic treatment of cases
Management of relapses

94
Q

Abrupt onset of nausea, vomiting, cramps and prostration

A

Staphylococcal food poisoning

95
Q

what is the incubation period of staphylococcal?

A

1-6hrs

96
Q

what are the diagnosis requirements?

A

Culture/enterotoxin detection in faeces and food(>10^5/g)

97
Q

what is the reservoir of the bacteria?

A

Contamination of ready to eat food from hands of food handler, followed by temperature abuse

98
Q

what disease does Bacillus cereus cause?

A

emetic syndrome
diarrhoeal syndrome

99
Q

incubation period of emetic syndrome?

A

1 to 5 hours

100
Q

incubation period of diarrhoeal syndrome?

A

8 to 16 hours

101
Q

how can it be diagnosed?

A

Culture (Food and faeces)

102
Q

what are the reservoirs?

A

No human or animal sources. Environment: soil, sediments, dust, vegetation and Food

103
Q

what food is commonly infected?

A

mainly rice dishes; occasionally pasta, meat or vegetable dishes, dairy products, soups, sauces, sweet pastry products.

104
Q

how is the bacteria transmitted to humans?

A

Contaminated cooked foods subjected to inadequate post-cooking temperature control during cooling and storage.

105
Q

Prodromal fever, headache, abdo pain, D for 1-2 weeks

A

Campylobacter sp

106
Q

what is the most common cause of Campylobacter sp infection?

A

food poisoning

107
Q

why are there vary in age distribution

A

20-49 more likely to eat out, take out, BBQ. More risk

108
Q

how many cases do the Infectious Intestinal Disease Survey (England) record annually?

A

9,500,000

109
Q

For every 136 cases in the community
how many present to GP?

A

23

110
Q

how many have a faecal sample tested?

A

6

111
Q

how many have a pathogen identified?

A

1.4

112
Q

how many is reported to CDSC?

A

1

113
Q

three main sources of intestinal disease annually?

A

Pecked doorstep milk
Foreign travel
Diarrhoeal dogs (32% positive)

114
Q

contamination in shop?

A

Cross contamination in retail premises
2/1132 cleaning cloths positive

115
Q

how can domestic kitchen hygiene go wrong and risk contamination

A

kitchen less than 2m in length
kitchen work surface less than 1m long
more than 3 hrs shopping to fridge
storing meat in top half of fridge
no separate chopping board for meat

116
Q

what is the incubation period of Giardia lamblia?

A

5 to 25 days.

117
Q

how is an infection diagnosed?

A

Light microscopy

118
Q

what are the reservoirs of bacteria?

A

Gastrointestinal tracts of people and animals.

119
Q

how is the infection transmitted?

A

Person to person.
Foodborne transmission is rare.
Faecal oral in young children. Waterborne.
Spread within families is common.

120
Q

what is the live form of the bacteria?

A

Giardia trophozoite

121
Q

what form is more common to see on microscopy?

A

Giardia cyst

122
Q

why cysts more common?

A

Cysts resist standard chlorination

medical microbiology (29 decks)

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