GI Infections

Question 1

General risk factors for GI infection?

Answer 1

Lack of clean water and poor sanitation

Overcrowding

Poor hygiene, esp. in children

Poor food preparation/storage and season factors

Question 2

Host risk factors for GI infection?

Answer 2

Age (very young and very elderly have increased risk)

Decreased gastric acid secretion (caused by drugs) and decreased gut motility

Influence of colonic microflora

Intestinal immunity

Question 3

Infectious dose required of different organisms to cause disease?

Answer 3

E. coli has a very low infectious dose (likely in the single figures)

Shigella, Giardia, Cryptosporidium have an infectious dose from low figures into the 100s

Salmonella, Campylobacter, Vibrio cholera have infectious doses in the 1000s

Question 4

Which organisms, bacterial, viral and parasitic, are seen in the UK compared to the organisms imported from abroad?

Answer 4

Question 5

Definition of diarrhoea?

Answer 5

3 or more loose stools in 24 hours

Question 6

How is the type of stool passed documented and describe the chart?

Answer 6

Question 7

Definition of the source/reservoir of an infection?

Answer 7

Original source of the infection, e.g: source of E.coli O157 is the GI tract of cattle

Question 8

Definition of the vehicle of an infection?

Answer 8

Means by which the infection is transmitted from one person to the next, e.g: contaminated food/water

Question 9

Describe the table of common organisms for UK GI infection

Answer 9

ADD PICTURE OF TABLE

Question 10

What does verotoxin do?

Answer 10

Produced by E. coli O157 and binds to receptors found on renal cells, erythrocytes and others; inhibit protein synthesis and cause cell death

Question 11

Clinical presentation of Haemolytic-Uraemic Syndrome (HUS)?

Answer 11

Abdominal pain

Fever

Pallor and petechiae (haemorrhages in skin)

Oliguria (↓urine production)

Majority of the time, there is bloody diarrhoea as well

Question 12

Describe occurrence of HUS?

Answer 12

Most cases are in those under 16 years old; children (< 5 years) and the elderly are the most likely to be infected

Peak presentation is at 7-10 days after onset of diarrhoea, so blood tests must be done at this time

Question 13

Blood tests for HUS reveal?

Answer 13

High leukocyte count

Low platelets

Low Hb

Erythrocyte fragments

Lactate dehydrogenase will be increased (greater than 1.5 times the normal value)

An FBC, blood film and U&Es must be done

Question 14

Salmonella, Shigella and E.coli O157 are all gram negative organisms; how are they differentiated?

Answer 14

Biochemical and serology tests

Question 15

Which GI infections are assoc. with ingestion of a pre-formed toxin?

Answer 15

Staph. aureus

Clostridium perfringens

Bacillus cereus

Question 16

What is a short incubation period and which organisms does this include?

Answer 16

1-6 hours

Staph. aureus and Bacillus cereus

Question 17

What is a medium incubation period and which organisms does this include?

Answer 17

12-48 hours

Salmonella and Cl. perfringens

Question 18

What is a long incubatio period and which organisms does this include?

Answer 18

2-14 days

Campylobacter and E. coli O157

Question 19

Taking a GI infection history?

Answer 19

Frequency & type of stool (Bristol Stool chart)

Travel outside the UK (which countries) and living conditions when abroad

Contact with animals

Question 20

Sending a stool sample?

Answer 20

At least one pea-sized specimen each for microscopy, toxin testing, culture (do NOT fill the container to the top)

Separate specimen required for virology

Vomit swab also acceptable for norovirus testing

Mention where the patient has been, if abroad

Question 21

Which microorganisms are diagnosed by which methods?

Answer 21