Week 8 - Epidemiology

Question 1

What is the symptoms and pathophysiology of cholera?

Answer 1

1. Symptoms:
   a) Massive amount of clear diarrhoea
   b) Dehydration
   c) Can be a mild infection
2. Pathophysiology:
   a) All symptoms caused by enterotoxin
   b) Bacteria does not invade cell or intestinal wall, must bind to specific receptors
   c) Toxin enters cells and causes Na+ to be actively pumped out of cells, chloride follows and then water follows salt by osmosis
3. Treatment:
   a) Oral vaccine
   b) Antibiotics not used because it is a toxin that does the damage not the bacteria
   c) Toxin is flushed out on its own however dehydration is dangerous (lose approx. 1L of water per hour) - Oral or IV re-hydration is essential

Question 2

What is the chain of infection?

Answer 2

1. Modes of transmission
2. What pathogen is involved
3. What is the host susceptibility (e.g. children and elderly more susceptible)
4. Modes of pathogen shedding (how does it move to other people e.g. incorrect handwashing when preparing food)
5. Reservoir host (some people can be host reservoirs)
6. Routes of entry (e.g. eating contaminated food)

Question 3

Describe food poisoning:

Answer 3

1. Illness from food spoilage or contamination with pathogenic bacteria, fungi, viruses, or parasites
   a) Contamination includes toxins produced by some of these organisms
2. Incubation period depends on the organism responsible

Question 4

What influences the infective dose in food poisoning?

Answer 4

1. Health of individual
   a) e.g. very young and old have decreased gastric pH and GIT motility
2. Medications taken
   a) e.g. previous antibiotic use or use of agents which change pH of stomach
3. Type of food
   a) e.g. fatty foods may act as barriers and protect organisms and/or toxins from penetration or delay penetration
4. Infection vs toxin
   a) e.g. C. perfringens infection can be mild however toxin has greater effect

Question 5

What does an epidemic curve show?

Answer 5

1. Epidemic pattern
2. Period of time over which persons are exposed
3. Incubation period for the disease

Question 6

What are the types of epidemic patterns?

Answer 6

1. Point source:
   a) Single pathogen
   b) All individuals were exposed at the same time
2. Intermittent Common
   a) Single pathogen
   b) Individuals were exposed at different times
3. Continuous Common
   a) Single pathogen
   b) Individuals were exposed continuously over a period of time

Question 7

How to establish an outbreak?

Answer 7

1. Clinical cases occur - gather information regarding these cases
2. Establish presence of epidemic
3. If epidemic is confirmed than either two ways can be done; Investigation component or Control component
   a) Investigation process would include; confirm diagnosis, conduct case finding, tract contact, conduct environmental assessment
   b) Control process includes; isolate and treat cases, attack source and transmission, prevention, continue surveillance
4. Mixture of investigation and control allows information to be compiled
5. Information is processed and analysed
6. Findings are communicated
7. Health plans for prevention of recurrence are established

Question 8

Describe Clostridium perfringens:

Answer 8

1. Type of pathogen: Bacteria
2. Symptoms
   a) Causes gastroenteritis (approximately 6-24 hours onset)
   b) Severe watery diarrhoea - risk of dehydration
   c) Abdominal distention (gas) which can cause cramps and explosive force with diarrhoea
   d) Severe decrease in BP which can lead to shock
3. Treatment:
   a) Fluids and rest
   b) Antibiotics not given as it is the toxin that causes damage
4. Prevention:
   a) Refrigerate cooked meat promptly
   b) Reheat meat thoroughly

Question 9

Describe Staphylococcus aureas:

Answer 9

1. Type of pathogen - Bacteria
2. Symptoms
   a) Severe nausea and vomiting (approximately 2-8 hours onset) - effect from heat stable toxin
   b) Occasionally fatal - especially very young, old, or immunocompromised
   c) Abdominal cramps and diarrhoea
   d) Severe fluid and electrolyte loss leading to decreased BP which can lead to shock
3. Treatment:
   a) Fluids
   b) Drugs to control nausea and vomiting
4. Prevention:
   a) Anyone with a skin infection should not prepare food for others until wound has healed

Question 10

Describe Giardia lamblia:

Answer 10

1. Type of pathogen: Parasite
   a) Faecal-oral route by this protozoan parasite
2. Symptoms:
   a) Stomach cramps and diarrhoea (approximately 1-2 weeks onset)
   b) Bloating
   c) Greasy stools
   d) Weight loss and dehydration
   e) Symptoms last 1-3 weeks
3. Treatment:
   a) Fluids and electrolyte replacement
   b) Flagyl (Metonidazol)
4. Prevention:
   a) Contamination when parasite or cysts come in contact with food or water or areas to prepare food
   b) Avoiding eating under cooked meat or drinking contaminated water

Question 11

Describe Norovirus:

Answer 11

1. Type of pathogen: Virus
   a) Direct Person to person transmission (e.g. sharing food or eating utensils)
   b) Food contamination by food handlers who have not washed their hands adequately
   c) Touching surfaces or objects contaminated with norovirus and then placing their hands in mouth or eating before washing hands
2. Symptoms:
   a) Severe nausea and vomiting (approx. 24-48 hours onset) - both faeces and vomit are infectious
   b) Violent vomiting without warning - several times in 24hrs period
   c) Dehydration
   d) Low grade fever
   e) Chills
   f) Muscle aches
3. Treatment
   a) Fluids
   b) Drugs to control nausea and vomiting
4. Prevention:
   a) Infected individuals must be excluded from general public until no vomiting or diarrhoea for 24 hours (for food handlers or food business - exclusion should be 48 hours without vomiting or diarrhoea)
   b) No swimming for infected individuals
   c) Appropriate hand hygiene after using bathroom, changing nappies, and before eating or preparing food
   d) Immediately remove and wash contaminated clothing or bedding and clean using hot water and soap
   e) Clean contaminated surfaces with detergent and then disinfect with bleach
   f) Flush or discard any vomit and/or faeces in toilet
   g) Babies and small children who are not toilet trained should wear waterproof nappies in swimming pools
   h) If faecal accidents occur in public pools, pools should be properly disinfected

Question 12

What should be done before preparing food?

Answer 12

1. Wash hands
2. Wash worktops
3. Wash dishcloths
4. Use separate chopping boards
5. Keep raw meat separate
6. Store raw meat on the bottom shelf of fridge
7. Cook food thoroughly
8. Keep fridge below 5 degrees Celsius
9. Cool leftovers quickly
10. Respect ‘use by’ dates